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The Modular Web Framework User`s manual

1. defines internal normal property rdf value 12 RDF s MWeb logic program rdf rb import rif rb rulebase 96 RDF Axiomatic triples rdf type rdf type gt gt rdf Property RDF compatibility with RIF rdf subject rdf type gt gt rdf Property 96 makes and rdf type equivalent rdf predicate rdf type gt gt rdf Property rdf object rdf type gt gt rdf Property 2X Y X rdfttype gt gt Y rdf first rdf type gt gt rdf Property X rdf type gt gt Y X Y rdf rest rdf type gt gt rdf Property rdf value rdf type gt gt rdf Property RDF Entailment rule rdf nil rdf type gt gt rdf List Z rdf type gt gt rdf Property Z gt gt _ Handles container membership properties They are infinitely many The rule only takes effect if called explicitly with the object grounded X rdf type gt gt rdf Property External name atom X prolog External name atom concat rdf _ N X prolog External name is number atom N prolog The support of RDF entailment is immediate All the classes and properties defined in RDF are declared internal The property CURIE construct allows to declare RDF properties In fact this is syntactic sugar for the RIF frame CURIE gt gt resulting in better looking interface files and expects a binary context predicate A class declaration class CURIE isshort for
2. geo capital gt gt Y X http geography int Italy Y http geography int Rome X http geography int Croatia Y http geography int Zagreb no mwebQuery X geo Europ_Country rdfs subClassOf gt gt X no mwebQuery X X geo Country X http geography int Italy X http geography int Croatia X http geography int Egypt no mwebQuery X neg X geo Country no mwebQuery X X geo Europ_Country X http geography int Italy X http geography int Croatia no mwebQuery X X geo Country neg X geo Europ Country X http geography int Egypt no mwebQuery X Y X geo Europ Country X geo capital gt gt Y X http geography int Italy Y http geography int Rome X http geography int Croatia Y http geography int Zagreb no mwebQuery X geo Europ_Country X no The expected answers are obtained However the last query deserves some explanation Using rdf s subClassof one does not obtain answers because the property is declared internal and thus is not visible No naswer is obtained using 2 because 2 is included in rd s subClassof but not vice versa and the predicate is also invisible Be very careful when negating RIF frame formulas since the current parser only supports negation of frames with a single property So users cannot que
3. gt gt rdf Statement rdf object rdfs domain gt gt rdf Statement rdfs member rdfs domain gt gt rdfs Resource rdf first rdfs domain gt gt rdf List rdf rest rdfs domain gt gt rdf List rdfs seeAlso rdfs domain gt gt rdfs Resource rdfs isDefinedBy rdfs domain gt gt rdfs Resource rdfs comment rdfs domain gt gt rdfs Resource rdfs label rdfs domain gt gt rdfs Resource rdf value rdfs domain gt gt rdfs Resource rdf type rdfs range gt gt rdfs Class rdfs domain rdfs range gt gt rdfs Class rdfs range rdfs range gt gt rdfs Class rdfs subPropertyOf rdfs range gt gt rdf Property rdfs subClassOf rdfs range gt gt rdfs Class rdf subject rdfs range gt gt rdfs Resource rdf predicate rdfs range gt gt rdfs Resource rdf object rdfs range gt gt rdfs Resource rdfs member rdfs range gt gt rdfs Resource rdf first rdfs range gt gt rdfs Resource rdf rest rdfs range gt gt rdf List rdfs seeAlso rdfs range gt gt rdfs Resource rdfs isDefinedBy rdfs range gt gt rdfs Resource rdfs comment rdfs range gt gt rdfs Literal rdfs label rdfs range gt gt rdfs Literal rdf value rdfs range gt gt rdfs Resource rdf Alt rdfs subClassOf gt gt rdfs Container rdf Bag rdfs subClassOf gt gt rdfs Container rdf Seq rdfs subClassOf gt gt rdfs Container X rdf type gt gt rdfs ContainerMembershipP
4. http example orgZq X X a X c http example orgzr X eX c MWebAS solutions neg http example org q X 8 http example3 org X b X c http example orgzp X Error XSB Runtime Unhandled Exception mweb Inconsistent modular rulebases This example is formed by three rulebases depicted below Rulebase s1 Rulebase s2 Rulebase s3 rulebase http example1 org rulebase http example2 org rulebase http example3 org prefix ex http example org prefix ex http example org prefix ex http example org defines local normal ex p 1 defines global definite ex q 1 defines global normal ex q 1 defines global normal ex q 1 defines local normal ex r 1 uses normal ex q 1 ex p X ex q X ex q c ex q a neg ex q b neg ex r c neg ex q c ex r c The definition of global predicates in normal or closed modes is forbidden by the theoretical MWeb framework due to non monotonicity For compatibility with RIF and the underlying Prolog framework these are allowed in the implementation Users are warned in the console when such potentially problematic situations are found Detecting inconsistencies By design the implementation of the MWebWFS semantics does not check consistencies automatically because it uses a paraconsistent semantics while MWebAS performs checks before executing goals but taking into accou
5. All the three can be used independently by importing the corresponding files The semantics of the combination is the one adopted by RIF and specified in the W3C Candidate Recommendation RIF RDF and OWL Compatibility A triple s p o is syntactically represented by the RIF frame s p gt gt o In our implementation the erdf rulebase imports the rdfs rulebase and the rdfs rulebase imports the rdfrulebase The supporf of RIF primitives is guaranteed by the import of rif by the rdf modular rulebase For the sake of completeness we present next the MWeb s implementation of each rulebase for the different profiles or entailment regimes RDF s MWeb interface rdf mw rulebase http www w3 0rg 1999 02 22 rdf syntax ns prefix rdf http www w3 org 1999 02 22 rdf syntax ns import rif mw interface defines internal normal class rdf Property defines internal normal class rdf XMLLiteral defines internal normal class rdf List defines internal normal class rdf Statement defines internal normal class rdf Seq defines internal normal class rdf Bag defines internal normal class rdf Alt defines internal normal property rdf type defines internal normal property rdf subject defines internal normal property rdf predicate defines internal normal property rdf object defines internal normal property rdf first defines internal normal property rdf rest
6. Module http 3A 2F 2Feuropa 2Eeu compiled cpu time used 0 0160 seconds Compiling http 3A 2F 2Fsecurity 2Eint Preprocessing http 3A 2F 2Fsecurity 2Eint pl Module http 3A 2F 2Fsecurity 2Eint compiled cpu time used 0 0250 seconds Compiling http 3A 2F 2Fgov 2Ecountry Preprocessing http 3A 2F 2Fgov 2Ecountry pl Warning XSB Compiler http 3A 2F 2Fgov 2Ecountry Unused symbol 2 Module http 3A 2F 2Fgov 2Ecountry compiled cpu time used 0 0500 seconds yes Ignore the warnings and execute the query load test obtaining exactly the following output load test MWebWFS solutions Anne MWebAS solutions Anne Boris yes You are now ready to start learning to use the MWeb system 4 Overview and syntax of the MWeb framework MWeb rulebases are defined by an interface and a logic program By convention the current implementation of MWeb assumes that these are specified in files with extensions mw and rb respectively The MWeb rulebase interface specifies the predicates defined and visible to the outside world exported predicates as well as the used imported predicates The logic program of the rulebase defines by means of logic rules the meaning of the predicates defined in the rulebase By design principles all defined and used predicated must be declared The current implementation of the MWeb framework specifies rulebases in syntax very similar to Prolog with a slight use
7. X gt gt Z2 X rdf type gt gt erdf PositivelyClosedProperty X rdf type gt gt erdf TotalProperty Z1 mw Vocabulary Z2 mw Vocabulary naf Z1 X gt gt Z2 ZA X gt gt Z2 X rdf type gt gt erdf NegativelyClosedProperty X rdf type gt gt erdf TotalProperty Z1 mw Vocabulary Z2 t mw Vocabulary naf neg Z1 X gt gt Z2 96 Inference rule with complements neg S P gt gt 0 P erd complementOf gt gt Q S Q gt gt 0 neg S P gt gt 0 Q erdf complementOf gt gt P J S Q gt gt 0 S P gt gt 0 P erdf complementOf gt gt Q neg S Q gt gt 0 S P gt gt 0 Q erdf complementOf gt gt P neg S Q gt gt 0 96 ERDF axiomatic triples erdf complementOf rdfs domain gt gt rdf Property rdfs range gt gt rdf Property rdf type gt gt rdf Property erdf PositivelyClosedClass rdfs subClassOf gt gt rdfs Class erdf NegativelyClosedClass rdfs subClassOf gt gt rdfs Class erdf PositivelyClosedProperty rdfs subClassOf gt gt rdfs Class erdf NegativelyClosedProperty rdfs subClassOf gt gt rdfs Class erdf TotalClass rdfs subClassOf gt gt rdfs Class erdf TotalProperty rdfs subClassOf gt gt rdfs Class 15 Mark that declaring a class or property simultaneously positively and negatively closed has the same practical eff
8. X rdf type gt gt rdfs Class X rdfs subClassOf gt gt Y Y rdf type gt gt rdfs Class X rdfs subClassOf gt gt Y Z rdf type gt gt Y X rdfs subClassOf gt gt Y Z rdf type gt gt X X rdfs subClassOf gt gt X X rdf type gt gt rdfs Class X rdfs subClassOf gt gt Z X rdfs subClassOf gt gt Y Y rdfs subClassOf gt gt Z X rdf type gt gt rdf Property X rdfs subPropertyOf gt gt Y Y rdf type gt gt rd Property X rdfs subPropertyOf gt gt Y Z4 Y gt gt Z2 X rdfs subPropertyOf gt gt Y Z1 X gt gt Z2 X rdfs subPropertyOf gt gt X X rdf type gt gt rdf Property X rdfs subPropertyOf gt gt Z X rdfs subPropertyOf gt gt Y Y rdfs subPropertyOf gt gt Z X rdfs subClassOf gt gt rdfs Literal X rdf type gt gt rdfs Datatype X rdfs subPropertyOf gt gt rdfs member X rdf type gt gt rdfs ContainerMembershipProperty RDFS Axiomatic triples rdf type rdfs domain gt gt rdfs Resource rdfs domain rdfs domain gt gt rdf Property rdfs range rdfs domain gt gt rdf Property rdfs subPropertyOf rdfs domain gt gt rdf Property rdfs subClassOf rdfs domain gt gt rdfs Class rdf subject rdfs domain gt gt rdf Statement rdf predicate rdfs domain
9. _ CURIE By the recommendation governing RIF RDF compatibility the predicates 2 and rdf type should be made equivalent this is achieved by the first rules The only rule necessary for RDF entailment states that any predicate of a triple must have type rdf Property Then the axiomatic RDF triples are stated concluding with the special treatment of RDF container membership properties The RDF container membership properties are treated specially since they are infinitely many rdf _1 rdf _2 etc The rule only fires if the subject of the triple is bound at query time with an atom if you need to use these properties please include them on your vocabulary for performing appropriately closed and open world assumptions Our RIF dialect also supports externally defined terms External Term prolog to perform Prolog calls as shown in the implementation of equality the prefix name which is bound to the empty string is essential to avoid resolution against the default base IRI RDF Schema entailment is more complex to specify but immediate According to RIF RDF compatibility every RIF subclass instance is also an RDFS subClassOf instance but not vice versa Afterwards all the RDF schema inference rules and axiomatic triples are encoded container membership properties are treated as in the implementation of RDF No other special treatment is necessary expect for XML Literals which are not currently taken care as well as the other RIF an
10. intZUK fails The weak negations of these queries succeed We use here the fully expanded names of the prefixes in order to remind users that these are in fact the real names of the predicates and constants The constant http geography int UK can be added to all loaded rulebases by calling vocabulary predicate and different behaviour is obtained see the right hand side of the previous table By closed world assumption it is concluded that http geography int amp UK is not a country and so query neg geo Country geo UK succeeds and naf neg geo Country geo UK fails 23 Vocabulary can also be added to a particular rulebase E g a call of the form vocabulary geo UK 6 http geography int would have the same effect in the previous example The different reasoning modes The http geography int rulebase can also be queried in other reasoning modes illustrating the differences among them The definite regime is very similar to ordinary Prolog as users can check below Objective queries on regime d Default queries on regime d mwebQuery C X geo Country X wfs d http geography int Portugal http geography int Greece http geography int Canada http geography int China http geography int Egypt http geography int Croatia http geography int Austria gt lt gt lt XX X X OK Xx l no mwebQueryC X neg geo Countr
11. default search path mwebUnloadModule RulebaseIRI Removes the rulebase identified with RulebaseIRI from the MWeb shell This can be used when local predicates have been defined more than once mwebLoadModules ListOfRulebaseIRIs Calls mwebLoadModule 1 for each element in the argument list Also accepts a single RulebaseIRI as in mwebLoadModule 1 mwebLoadAllModules RulebaseIRI Convenience predicate to load recursively all the modules EXPLICITLY appearing in uses rulebase lists starting from RulebaseIRI and following the rulebases uses lists If a rulebase has been previously loaded then it is ignored Declarations prefix 1 Declares a set of prefixes to be used in the MWeb shell The prefix command expects a comma separated list of terms Prefix IRIRef The prefixes occurring in any loaded rulebase are NOT declared in the shell vocabulary 1 Declares extra vocabulary at the global level visible to all or to a specific rulebase It expects a comma separated list of constants with an optional Rulebase 42 Querying mwebQuery FreeVars Query Semantics Regime This is the main predicate for querying the MWeb system This predicate executes Query with free variables listed in FreeVars under Semantics in mode Regime The use of each argument is now detailed FreeVars in some queries it might be necessary to list the free variables in FreeVars to perform instantiation before querying in order to avoid floun
12. define such predicates Since they have not rulebase import lists most of the times it is necessary to explicit load the appropriate rulebases explicitly via the mwebLoadModule 1 command 18 7 Querying The MWeb querying interface is immediate to use via the several mwebQuery predicates For simplifying writing of queries users may declare prefixes at the console by using the same syntax of MWeb interface files prefix eu http europa euf geo http geography int yes The MWeb system declares initially useful prefixes by the following declarations prefix xs http www w3 0rg 2001 XMLSchema prefix rdf http www w3 org 1999 02 22 rdf syntax ns prefix rdfs http www w3 org 2000 01 rdf schema prefix rif http www w3 org 2007 rif prefix func http www w3 org 2007 rif builtin function prefix pred http www w3 org 2007 rif builtin predicate prefix owl http www w3 org 2002 07 owl Any prefix may be redefined by declaring again the new prefix The basic binary predicate mwebQuery FreeVars Query executes Query in normal regime using MWebWKFS semantics and by instantiating the free variables in FreeVars with all possible combinations of constants of the several vocabularies of the loaded rulebases The use of the free variables argument must be used when floundering occurs i e calls to non ground weakly negated literals occur during the
13. http geography int Italy X http geography int Greece no mwebQuery X neg X eu CountryEU no mwebQuery X naf X 4 eu CountryEU X http www travel org visit X http www pyramis gr package2 X http www travel_plan gr package2 X http geography int Luxor X http www travel org travel X http www pyramis gr package1 X http www travel_plan gr package1 X http www anne_travel_pref gr choose_trav_package X http geography int Trogir X http www anne_travel_pref gr visit_other no mwebQuery X naf neg X eu CountryEU X http geography int Italy X http geography int Greece plus the solutions of the previous query no mwebQuery X X geo Europ_Country X http geography int Italy X http geography int Croatia no mwebQuery X neg X geo Europ Country X http erdf org complementOf X http www w3 org 2000 01 rdf schema domain X http www w3 org 2000 01 rdf schema comment X http www w3 org 1999 02 22 rdf syntax ns _1 X http geography int Country no mwebQuery X naf X geo Europ Country X http erdf org complementOf X http www w3 org 2000 01 rdf schema domain X http www travel org visit X http www w3 org 2000 01 rdf schema comment X http www w3 org 1999 02 22 rdf syntax ns _1 mwebQuery X naf neg X geo Europ
14. thus is the appropriate mode for safe reasoning in the Semantic Web Moreover under MWebAS semantics it can generate alternative worlds and do reasoning by cases However it is less efficient than definite mode for both MWebWFS and MWebAS semantics Since constant France does not belong to the vocabulary context predicate fails then the same behaviour of the other modes is obtained Therefore undeclared vocabulary can bring semantic problems do not forget to declare all the vocabulary To conclude discussion if the predicate geo Country 1 is queried in normal mode then the used mode is in fact closed according to Table 4 because the predicate has been defined in closed mode Do not forget that this table is always used to obtain the real mode used to perform the query The different semantics Consider now the rulebase defining the European countries built on top of the geography rulebase The list of world countries is used to provide the context predicate for performing the closed world assumptions in all respects this is very similar to the geography rulebase 25 Europa s MWeb interface europa mw Europa s MWeb logic program europa rb rulebase http europa eu eu CountryEU geo Austria eu CountryEU geo Greece prefix eu http europa eu eu CountryEU geo Portugal geo http geography int defines local closed eu CountryEU 1 wrt context geo Country 1 uses definite ge
15. Country X http www travel org visit X http geography int Greece X http www pyramis gr package2 Since http geography int Europ_Country is closed with respect to the vocabulary of http geography int the solutions of the last two queries in open mode present some solutions with vocabulary of other rulebases ERDF always uses the whole available vocabulary for open and closed world assumptions The declaration of total properties is done in the same way by stating that the property has rdf type erdf TotalProperty Closed properties are declared using erdf PositivelyClosedProperty and erdf NegativelyClosedProperty depending on the intended semantics 32 Global predicates Travel packages are expressed in the following two rulebases http www pyramis gr and http www travel_plan gr whose definition can be found next Pyramis rulebase Travel rulebase rulebase http www pyramis gr base http www pyramis gr prefix geo http geography int vac http www travel org pyr http www pyramis gr import erdf mw interface defines global normal property vac travel defines global normal property vac visit rulebase http www travel plan gr base http www travel plan gr prefix geo http geography int vac http www travel org trav http www travel_plan gr import erdf mw
16. The Modular Web Framework User s manual Carlos Viegas Dam sio Anastasia Analyti and Grigoris Antoniou 1 Introduction The Modular Web Framework MWeb allows the use and combination of several rulebases in a principled way supporting safe uses of non monotonic negation in scoped closed and open world assumptions in logic rules for Semantic Web applications Currently it supports experimentally RDF Schema ontologies and is integrated with the state of the art inference engines XSB and Smodels Support of RIF and Integration with OWL 2 is foreseen in the near future MWeb s main features are Safe support of monotonic strong and non monotonic weak or naf negations under full control of rulebase providers and consumers Immediate specification of scoped open and closed world assumptions independently of the existing or shared rulebases Full fledged theory and results guaranteeing monotonicity under broad conditions Independent interpretations of shared knowledge via explicit or implicit export and import directives Adoption and transparent use of main semantics for logic rule bases well founded and answer set based Detection of knowledge dependent on contradictions Separate interface and rulebase module code Embellished Prolog like syntax for simplifying rulebase development Modular and independent compilation of modules with dynamic loading Compilation into XSB prolog modules with tabling to guarantee termination and
17. V1 V V1 11 RIF predicates are declared internal in order to prevent disclosure of unintended information Users can then make visible instances of particular predicates or classes by declaring them local or internal The special class mw Vocabulary collects all the defined vocabulary implicitly or explicitly in vocabulary declarations Class inheritance is captured by the first rule in file rif rb Mark the need to have a rule for taking care of the case where it is known that something does not belong to the extension of some class second rule For subclass relation it is only required transitivity transitivity does not have a dual negative rule Frames do not have any special meaning thus no rules are needed to capture them The most difficult predicate to capture is equality Our approach is designed to handle correctly equality among constants no recursion on arguments is performed For instance if some user states that a b and b c the consequence c a is obtained but not f a f c The OWL 2 RL rules of equality can be easily captured Users wishing to use RIF should import the files rifmw and rif rb into their MWeb interface and logic program files respectively see example in the next subsection ERDF support The MWeb s implementation of the Extended Resource Description Framework builds on the RIF frame constructs and is made in three stages rdf support rdfs support and finaly erdf support
18. X Vocabulary no mwebQuery X naf neg ex p X X a X b X C X Vocabulary no 37 From the above results it can be concluded that conclusion http example org p c depends on contradiction since both http example org p c and naf http example org p c hold but is not itself contradictory because the conclusion neg http example org p c does not hold Let s compare to what happens to predicate ex q 1 mwebQuery X ex q X a Cc x Won mwebQuery X neg ex q X b c logon x rx 385 mwebQuery X naf ex q X b c log o5 Xr 25 mwebOuery X naf neg ex q X a c log n x x D Notice that http example org p c andneg http example orgfp c hold thus we have contradiction This can be checked directly or by decting the dependencies on contradiction since by coherence naf http example org p c andnaf neg http example org p c both hold as expected As shown before MWebWFS is tolerant to the existence of contradictions but is capable of signalling their effects MWebAS is not paraconsistent but in some circumstances is capable of isolating independent parts of the rulebases avoiding trivialization in expected situations Global and local models The MWeb framework is designed in such a way that each rulebase has its own interpretation of all defined and used predicates for each regime This prevents
19. aphy int Austria P Boris C http geography int Croatia no mwebQuery P naf sec Suspect P P Rita no mwebQuery P naf neg sec Suspect P P Peter no Finally rulebase http gov country expresses some rules to allow entering into an imaginary country resorting to all the previous rulebases Gov s MWeb interface gov mw Gov s MWeb logic program gov rb rulebase http gov country prefix gov http gov country prefix eu http europa eu prefix geo http geography int prefix sec http security int defines local normal gov Enter 1 visible to http security int defines local closed neg gov RequiresVisa 1 wrt context geo Country 1 uses definite geo Country 1 from http geography int uses open eu CountryEU 1 from http europa eu uses definite sec citizenOf 2 sec Suspect 1 from http security int uses normal class mw Vocabulary defines internal open sec citizenOf 2 gov Enter P eu CountryEU C sec citizenOf P C sec Suspect P http security int gov Enter P eu CountryEU C sec citizenOf P C gov RequiresVisa C sec Suspect P http security int gov RequiresVisa geo Croatia sec citizenOf Peter geo Greece 27 The rulebase shows other important features of the MWeb framework First users can al
20. ase http www anne travel pref gr expresses Anne s travel preferences Anne s rulebase defines only one predicate in normal mode which is visible only to Peter s rulebase The logic program captures the following conditions to select travel packages 1 A package is chosen by Anne if it travels to a non European country according to geography s rulebase and visits only one city according to pyramis travel agency This is captured by the first and the second rules in the program 2 Atrip to an EU Country by Travel Plan which visits at least two cities third rule 3 Atrip to an European but not a EU Country that visits the capital of the country fourth rule Anne s MWeb interface anne mw Anne s MWeb logic program anne rb rulebase http www anne travel pref gr base http www anne travel pref gr prefix ann http www anne travel pref gr prefix geo http geography int eu http europa eu prefix vac http www travel org trav http www travel plan gr import erdf mw interface defines local normal property ann choose_trav_package visible to http www peter travel pref gr uses normal property vac travel uses normal property vac visit uses normal property geo capital from http geography int uses normal class geo Europ Country from http geography int uses normal class eu CountryEU from http europa
21. cateInd neg PosPredicateInd PosPredicateInd CURIE NATURAL Atom classC CURIE propertyC CURIE Rulebaselist RulebaseIRI RulebaseIRI RulebaselRI IRIRef CURIE PREFIX LOCALNAME IRIRef PREFIX Name LOCALNAME Name IRIRef Name N PROLOGCHAR N Const PROLOGCONST PROLOGCHAR CURIE The defines declaration starts with the scope specifying the span of a predicate Next the regime reasoning mode should be mandatorily specified Several predicates can be specified with a single defines declaration Afterwards an optional context predicate can be given for the objective and closed modes ignored in the other cases Finally visibility can be controlled by providing an explicit list of rulebases which can use the predicates if absent the predicates defined can be used by any rulebase The defines declaration is synthesized on Table 3 The meaning of class and property constructs is explained in the ERDF section of this document where syntax is expanded to cater for RIF frames However it should be noticed that it is expected a unary context predicate for classes and a binary one for properties more discussion on the examples section The previous EBNF grammar is dependent on the following symbols PROLOGCHAR PROLOGCONST Name and Atom The terminal PROLOGCHAR matches Prolog characters briefly ASCII character The terminal PROLOGCONST matches any a
22. cates under normal regime XSB builtins can also be used by importing from the appropriate module or usermod for inline predicates The use of parenthesis is mandatory mark the extra space Finally notice that a predicate can be defined and used in the same MWeb interface file by allowing users to redefine a particular implementation of a predicate defined elsewhere In particular if defined in internal scope even local predicates can be used internally and redefined in other rulebases The MWeb Logic Program The syntax of MWeb rulebases is very similar to Prolog with some single exceptions in order to approximate the syntax to the one used by RIF The summary of the syntax is collected on Table 5 and Table 6 The syntax will be extended subsequently to handle RIF syntax in particular RIF frames equality class membership and subclass relation see Section 5 for more details Additionally the MWeb logic program allows the definition of internal predicates as well as inline importing of other MWeb logic programs The general syntax is covered by the grammar on Table 5 Table 5 Syntax of MWeb logic programs MWebLogicProgram Statement Statement Import DefinesInternal Rule Import import FileName rulebase DefinesInternal defines internal RegimePred wrt context PredicateInd The definition of internal predicates is explained in the previous secti
23. country Enter P asp P Peter no mwebQuery P naf neg http gov country Enter P asp P Rita P http geography int Portugal P http geography int UK P Anne P http geography int Greece P http geography int Canada P Peter P http geography int China P Boris P http geography int Egypt P http geography int Croatia P http geography int Austria P Vocabulary no Under MWebWFS and MWebAS we conclude that Anne is allowed to enter the country since she is a citizen of Austria an European country and she is not believed suspect of any criminal actions However we can only conclude that Boris is allowed to enter the country using MWebAS This is so because we need to do some case analysis consider multiple possible models It is known that Boris is a citizen of Croatia and is not suspect However we do not know if Croatia is a European country Since predicate eu CountryEU 1 is used in open mode the MWebDAS semantics considers a model where Croatia is an European country and thus Boris can enter by the first rule and considers another model where Croatia is not an European country but since it is not required a Visa for Croatia Boris can also enter the country in this case by the second rule Since in all possibilities Boris can enter the country by cautious reasoning we conclude that it is safe to allow Boris enter the country Since there are no rule
24. d XML Schema datatypes RDFS MWeb interface rdfs mw rulebase http www w3 org 2000 01 rdf schema prefix rdfs http www w3 org 2000 01 rdf schema defines internal normal property rdfs domain import rdf mw interface defines internal normal property rdfs range defines internal normal property rdfs subClassOf defines internal normal class rdfs Resource defines internal normal property rdfs subPropertyOf defines internal normal class rdfs Literal defines internal normal property rdfs member defines internal normal class rdfs Datatype defines internal normal property rdfs comment defines internal normal class rdfs Class defines internal normal property rdfs seeAlso defines internal normal class rdfs Container defines internal normal property rdfs isDefinedBy class rdfs ContainerMembershipProperty defines internal normal property rdfs label 13 RDFS MWeb logic program rdfs rb import rdf rb rulebase 96 RDFS compatibility with RIF requires including into rdfs subClassOf X rdfs subClassOf gt gt Y X Y 96 RDFS entailment rules Z rdf type gt gt Y X rdfs domain gt gt Y Z X gt gt W W rdf type gt gt Y X rdfs range gt gt Y Z X gt gt W X rdfs subClassOf gt gt rdfs Resource X rdf type gt gt rdfs Class
25. d calls to process mweb uses mode 5 Specialising partially instantiated calls to process mweb atom 6 Specialising partially instantiated calls to process curie 3 Specialising partially instantiated calls to process strong negation 2 Specialising partially instantiated calls to process slots 3 Specialising partially instantiated calls to process and slots 3 Specialising partially instantiated calls to expand mweb atom 6 Module mwebParser compiled cpu time used 0 1400 seconds Compiling Users carlosdamasio Documents Codigo mweb mwebCompiler Specialising partially instantiated calls to mwebLocalPredicateName 3 Specialising partially instantiated calls to mwebEncodeLiteral 4 Specialising partially instantiated calls to mwebCompileListUses 3 Specialising partially instantiated calls to mwebCompileOneUses 7 Specialising partially instantiated calls to mwebExportDeclarations 5 Specialising partially instantiated calls to mwebCompileLiteral 4 Specialising partially instantiated calls to mwebPredicateName 5 Specialising partially instantiated calls to mwebDualPrologPredicate 1 Module mwebCompiler compiled cpu time used 0 0900 seconds mwebCompiler loaded Compiling Users carlosdamasio Documents Codigo mweb mwebRuntime Module mwebRuntime compiled cpu time used 0 0040 seconds mwebRuntime loaded dP dP dP dP dP dP oo End XSB cputime 0 32 secs elapsetime 0 38 secs Check that the installation is fin
26. ded RDF Schema ontologies in XML and NTriples serialization formats including automatic support and renaming of blank nodes Rulebases specified in Rule Interchange Format both in presentation and normative XML syntax 40 Support of the basic OWL2 profiles namely OWL2 RL which has a specification on RIF Mechanisms for ontology mapping in particular mapping of constants in different rulebases Development of a paraconsistent semantics for MWebAS 41 10 Library Predicates Compilation mwebCompileModule RulebaseName Compiles a rulebase The RulebaseName is used to generate the file names of the interface and logic program files by encoding it and appending the suffixes mw and rb respectively Encoding escapes all chars except for letters digits HYPHEN MINUS and LOW LINE The mwebCompileModule 2 is then called for performing the compilation mwebCompileModule InterfaceFile RulesFile A prolog module will be generated and compiled The name of the Prolog file is obtained from the rulebase declaration in the interface source file The Prolog file has pl extension and filename obtained by escaping all chars except for letters digits HYPHEN MINUS and LOW LINE ofthe rulebase IRI Loading mwebLoadModule RulebaseIRI Loads a given rulebase identified by RulebaseIRI into the MWeb shell The corresponding Prolog file with encoded RulebaselIRI filename and pl extension must be in XSB s
27. dering problems calls of weak negation with non ground arguments Users may try first calling with an empty list and then include the necessary variables to avoid errors Query the query to be executed More details can be found in the previous sections Semantics either the constant wfs or asp selecting respectively MWebWFS or MWebAS semantics to be used In order to query under MWebAS semantics XSB system must be compiled with smodels support It is always possible to query with MWebWKEFS semantics which is the default mode Regime selects the MWeb querying mode d for definite o for open c for closed or n for normal The default mode is n mwebQuery Query The same asmwebQuery Query wfs n mwebQuery FreeVars Query The same as mwebQuery FreeVars Query wfs n mwebQuery FreeVars Query Semantics The same as mwebQuery FreeVars Query Semantics n mwebSetErrorLevel Level Flag to control runtime behaviour when call of a normal predicate is made from a non normal predicate definite open or closed Level can be one of error msg or none If error is set the default a runtime error is thrown if msg is set then a warning message is written in the console otherwise the computation continues silently level none Consistency Checking mwebCheckConsistency Semantics Regime Checks global consistency of all loaded rulebases under Semantics and mode Regime Semantics takes value
28. discover that UK is in fact an European Country The rulebase http security int defines citizenship and suspects of criminal acts Both predicates are defined open However citizenship relations are only visible to the rulebase identified by http gov country 26 Security s MWeb interface security mw Security s MWeb logic program security rb rulebase http security int prefix sec http security int geo http geography int defines local open sec citizenOf 2 visible to http gov country defines global open sec Suspect 1 defines global normal class mw Vocabulary uses normal class mw Vocabulary sec citizenOf Anne geo Austria sec citizenOf Boris geo Croatia sec Suspect Peter neg sec Suspect Rita The relevant queries to our example are found below and the expected behaviour is obtained since all predicates are declared open Objective queries Default queries mwebQuery P C sec citizenOf P C P Anne C http geography int Austria P Boris C http geography int Croatia no mwebQuery P C neg sec citizenOf P C no mwebQuery P sec Suspect P P Peter no mwebQuery P neg sec Suspect P P Rita no mwebQuery P C naf sec citizenOf P C no mwebQuery P C naf neg sec citizenOf P C P Anne C http geogr
29. e a model In particular in face of contradictions everything is entailed from the program and users are informed of inconsistency This semantics is computationally more expensive entailment is coNP complete and thus more expressive see the examples 10 5 Experimental Support of RIF and E RDF Schema The MWeb implementation is currently being extended to support both a dialect as specialization of the Rule Interchange Format RIF and the Extended Resource Description Framework Schema ERDF In order to maintain compatibility with RIF and generality all properties and classes are assumed to be normal allowing for the use of weak negation in the bodies However as expected monotonicity is not guaranteed The implementation of these extensions is done through MWeb rulebases where the interface and meaning can be entirely defined within MWeb This demonstrates the simplicity usefulness and generality of our approach A preliminary implementation is available for testing and already interesting behaviour can be obtained RIF support The supported dialect implements fully the semantics of classification member and subclass frames and partially equality Regarding connectives the usual binary boolean connectives conjunction and disjunction as well as strong and weak negations are supported under Paraconsistent Well founded Semantics with Explicit Negation and Answer Set Semantics No disjunction is allowed in the heads of r
30. e by cding to USERDIR mweb examples security and consulting file testSecurity The output should be similar to testSecurity Compiling testSecurity testSecurity compiled cpu time used 0 0130 seconds testSecurity loaded mweb loaded xasp loaded sm clause store loaded mwebParser loaded fancyProlog loaded iri loaded iriparse loaded utilities loaded builtins loaded mwebCompiler loaded mwebRuntime loaded Compiling http 3A 2F 2Fgeography 2Eint Preprocessing http 3A 2F 2Fgeography 2Eint pl Module http 3A 2F 2Fgeography 2Eint compiled cpu time used 0 0150 seconds Compiling http 3A 2F 2Feuropa 2Eeu Preprocessing http 3A 2F 2Feuropa 2Eeu pl Warning XSB Compiler http 3A 2F 2Feuropa 2Eeu Unused symbol rbnaf 1 Warning XSB Compiler http 3A 2F 2Feuropa 2Eeu Unused symbol 2 Warning XSB Compiler http 3A 2F 2Feuropa 2Eeu Unused symbol tneg_http geography int Country 2 Warning XSB Compiler http 3A 2F 2Feuropa 2Eeu Unused symbol usermod 0 Warning XSB Compiler http 3A 2F 2Feuropa 2Eeu Unused symbol tpos_http geography int Country 2 Warning XSB Compiler http 3A 2F 2Feuropa 2Eeu Unused symbol tupos http geography intZCountry 2 Warning XSB Compiler http 3A 2F 2Feuropa 2Eeu Unused symbol 68 2 Warning XSB Compiler http 3A 2F 2Feuropa 2Eeu Unused symbol tuneg http geography intZCountry 2
31. e countries Chttp geography int Country mwebQueryC X X geo Country X http geography int Italy X http geography int Egypt X http geography int Croatia no The entities X which are countries Chttp geography int Country now using RIF frames mwebQuery X X rdf type gt gt geo Country X http geography int Italy X http geography int Egypt X http geography int Croatia no Finding the capitals Y of countries X mwebQuery X rdf type gt gt geo Country geo capital gt gt Y gt lt ll http geography int Croatia Y http geography int Zagreb x lt ll http geography int Italy Y http geography int Rome X http geography int Egypt http geography int Cairo lt l no Itis only possible to call rdf type in the previous two queries because property rdf type has been made global by one of the rulebases otherwise no answer would be obtained Users can also work directly with RIF frame internal predicate gt Attribute Object Value obtaining the same results as the query Object Attribute gt gt Value as per the example below If the free variables list is empty a more convenient unary version of the mwebQuery Query command is available Obtains all the triples which have geo Italy as object mwebQuery gt Pred Subj geo Italy Pred http www travel org travel Subj h
32. ect as declaring it total The handling of closed classes and properties is a recent advancement not yet reported in the literature ERDF requires extra rules to take care of negative extensions for RDF and RDFS properties Most ofthe rules having strong negation in the heads are in fact capturing the ERDF dual rules of RDF and RDFS entailment Finally by declaring two properties complementary the positive and negative instances are exchanged as the erdf rb MWeb logic program file shows The axiomatic triples of ERDF are also included Blank nodes in user theories are captured by declaring them typed literals of symbol space rif local and are local to the files where they occur In a similar way we expect to capture the OWL 2 RL profile by implementing the full set of OWL 2 RL RDF rules 16 6 Use After downloading and confirming correct installation see Section 3 itis necessary to load the system by consulting the mweb file An usual session consists of compiling the rulebases loading in the corresponding Prolog modules and then querying the loaded rulebases Each of these steps is now detailed Compilation After developing your MWeb rulebases it is necessary to compile them The compilation can be done independently for each rulebase and in any order The name of the rulebase is used to generate the file names of the interface and logic program files by encoding it and appending the suffixes mw and rb respectively A pr
33. ed predicate in the list The binding of variables of the context predicate with the defined predicates can be implicitly left to right using arity or explicit using explicit variables If absent the open and closed world assumptions are done with respect to the vocabulary of any loaded rulebase visible to RulebaseList Limits the use of the non internal predicates to the rulebases in the specified comma separated list If absent the non internal predicates can be used by any rulebase The uses declaration is simpler to use and just requires the expressing of the import regime and the provider rulebases If the rulebase list is absent then the predicate is imported from any loaded rulebase defining the predicate in either global or local scope The regime of the used predicate is combined with the regime of the defined declaration in order to obtain the regime followed at query time The rules for obtaining the regime are condensed on Table 4 roughly meaning that it is used the least regime of the use and defines declaration where regimes are totally ordered by definite open closed normal The X marks an error condition which can be disabled with a call to mwebSetErrorLevel none Table 4 Combination of regime modes dididid X lo ldiolo X SicldiolciX nidjoci n djoj jcjn defines It is also provided a declaration that can be used to import XSB prolog predi
34. efficiency Seamless integration with XSB Prolog system with no overhead 2 Copyright and Contacts Copyright 2009 Carlos Viegas Dam sio MWeb is free software you can redistribute it and or modify it under the terms of the GNU General Public License as published by the Free Software Foundation either version 3 ofthe License or at your option any later version MWeb is distributed in the hope that it will be useful but WITHOUT ANY WARRANTY without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE See the GNU General Public License for more details You should have received a copy of the GNU General Public License along with MWeb If not see lt http www gnu org licenses gt The MWeb software has been developed by Carlos Viegas Damasio cd di fct unl pt Centro de Intelig ncia Artificial CENTRIA Faculdade de Ci ncias e Tecnologia Universidade Nova de Lisboa Quinta da Torre 2829 516 Caparica Portugal The MWeb framework is a joint work of Anastasia Analyti Grigoris Antoniou Carlos Viegas Damasio with contributions from Gerd Wagner More information can be found at MWeb s web page http centria di fct unl pt cd mweb 3 Download and installation The MWeb framework assumes that XSB Prolog version 3 2 or later is properly installed with Smodels support The XSB system can be obtained from http xsb sourceforge net The Smodels system is distributed with XSB but users can obtain
35. eral prefix declarations can occur sequentially in the same interface file The contents of other MWeb interface files can be in place inserted via the import declaration For the time being the file should be in the machine s file system and cannot be loaded from the Web Do not forget the parenthesis The users can declare domain constants by resorting to the optional vocabulary declaration Notice that all constants found in the corresponding rulebase logic program are automatically added to the rulebase vocabulary without any user intervention However for some applications it might be necessary to declare extra constants not found in the logic program The MWeb interface file continues with a sequence of defines declarations and uses declarations which roughly correspond to export and import declarations respectively These declarations are detailed on Table 2 and the syntax is given by an EBNF grammar Table 2 Grammar of defines and uses declarations DefinesDecl defines ScopeDecl RegimePred wrt context PredicateInd visible to Rulebaselist UsesDecl uses RegimePred from Rulebaselist import C C definite normal Predicatelist from RulebaseIRI ScopeDecl global local internal RegimePred definite open closed normal PredicateList Predicatelist PredicateInd Predicatelist PredicateInd PosPredicateInd NegPredicateInd NegPredi
36. es In fact only classes that require context literals must be declared However properties for which we have rules must always be declared A class declaration class CURIE is short for _ mw Vocabulary coinciding with rdf type gt gt CURIE Recall that in MWeb ERDF all classes and properties normal and notice that the rdf s properties are declared elsewhere and imported both in the interface file declarations and logic program rules Observe also how triples frames for the same subject can be aggregated together The intended semantics of this rulebase is also pretty clear we have a positively closed list of European Countries some instances are listed as well their capitals 30 Some interesting queries illustrating some features are shown next ERDF queries using RIF frames ERDF queries using RIF relations mwebQuery X X rdf type gt gt geo Country X http geography int Italy X http geography int Croatia X http geography int Egypt no mwebQuery X neg X rdf type gt gt geo Country no mwebQuery X X rdf type gt gt geo Europ Country X http geography int Italy X http geography int Croatia no mwebQuery X X rd type gt gt geo Country neg X rdf type gt gt geo Europ Country X http geography int Egypt no mwebQuery X Y X rdf type gt gt geo Europ_Country
37. eu uses normal class mw Vocabulary import erdf rb rulebase Package ann choose trav package gt gt Country neg Country geo Europ Country Package vac travel gt gt Country Package vac visit gt gt City http www pyramis gr naf neg Package ann visit other gt gt City neg Package ann visit other gt gt City Package vac visit gt gt City http www pyramis gr Package vac visit gt gt Other http www pyramis gr naf City Other Package ann choose trav package gt gt Country Package vac travel gt gt Country Package vac visit gt gt City1 http www travel plan gr Package vac visit gt gt City2 http www travel plan gr naf City1 City2 Package ann choose trav package gt gt Country Country rdf type gt gt geo Europ Country neg Country rdf type gt gt eu CountryEU Package vac travel gt gt Country Package vac visit gt gt City City geo capital gt gt Country Since all properties and classes are normal then negation as failure can be used to capture universal quantification This allows for greater generality but with no monotonicity guarantees Mark that the interface uses normal properties vac travel and vac visit without stating their provenance while in the logic program part of the rulebase some of the queries ment
38. execution in particular when naf is applied to non ground literals in the query Usually for MWebWFS you can pass an empty list which is more efficient If you get an execution error then put the variables in the FreeVars list Naturally the command line does not support the fancy syntax so users should keep to Prolog conventions Some example queries are shown below including the RIF and ERDF syntax The full explained examples can be found in Section 8 We show some examples with the basic syntax using the security example rulebase Determines the pairs of citizen X of country Y mwebQueryC X Y http security int citizenOf X Y X Anne Y http geography int Austria X Boris Y http geography int Croatia no Determines the countries Y which are know to not being European Union countries xX mwebQuery neg eu CountryEU Y http geography int Egypt http geography int Canada http geography int China http geography int Croatia lt lt lt 19 Determines the citizens X of non European Union countries Notice the use of parenthesis for complex queries and for querying specific rulebases mwebQueryC C http security intZcitizenOf X Y C neg eu CountryEU Y 8 http europa eu X Boris Y http geography int Croatia no The next examples show the combination of the RIF syntax with RDF Schema support The entities X which ar
39. further information at http www tcs hut fi Software smodels After that download the tgz archive from http centria di fct unl pt cd mweb and unpack it in a directory of your choice let s denote it by USERDIR mweb For simpler use we suggest the following line to be added to your xsbrc P file usually located in xsb directory do not forget the quotes assert library directory USERDIR mweb source Compile the MWeb framework with the command xsb mweb You should obtain in the output something like ignore any warning messages that might exist the following sequence of text parts have been removed xsb mweb xsb configuration loaded sysinitrc loaded siteinitrc loaded xsbrc loaded Compiling Users carlosdamasio Documents Codigo mweb mweb Specialising partially instantiated calls to mwebExecuteGoal 4 Specialising partially instantiated calls to mwebCompileGoal 4 Specialising partially instantiated calls to ord_union 3 mweb compiled cpu time used 0 0730 seconds xasp loaded sm_clause_store loaded Compiling Users carlosdamasio Documents Codigo mweb mwebParser Specialising partially instantiated calls to declare prefixes 3 Specialising partially instantiated calls to process mweb scope 5 Specialising partially instantiated calls to process mweb predicate 4 Specialising partially instantiated calls to process mweb defines predicates 8 Specialising partially instantiate
40. idden Similar to Horn programs but with strong negation allowed with closed world assumption normal Arbitrary rules with monotonic strong neg and non monotonic weak naf negation Conclusions are non monotonic Corresponds to extended logic programs PredicateList Specifies the comma separated list of the defined predicates Each predicate can have the keywork neg before it This keyword is used in regime closed to indicate that the predicate is negatively closed otherwise it is ignored Prefix Local N Prefix Local A1 An Defines a predicate with N arguments with name constructed by appending the namespace IRI with Local An IRIref should be obtained unless the reserved prefix atom is used Defines a predicate with n arguments with name constructed by appending the namespace IRI with Local A valid IRIref should be obtained The list of arguments is explicitly provided and can be used to bind arguments with the context predicate Local N Local A1 An The same as before but it is appended to the default base IRI to construct the name For compatibility with Prolog if there is no base IRI then Local is used as name A valid IRI reference should be obtained wrt context PredicateInd Specifies an optional context predicate for the open or closed world assumptions of objective and closed regimes The arity number of arguments of this predicate must be the same as any defin
41. interface defines global normal property vac travel defines global normal property vac visit import erdf rb rulebase pyr package1 vac travel gt gt geo Egypt vac visit gt gt geo Cairo pyr package2 vac travel gt gt geo Egypt vac visit gt gt geo Cairo vac visit gt gt geo Luxor import erdf rb rulebase trav package1 vac travel gt gt geo ltaly vac visit gt gt geo Rome trav package2 vac travel gt gt geo Croatia vac visit gt gt geo Zagreb vac visit gt gt geo Trogir We can query to obtain which packages travel to which countries independently where they are defined mwebQuery X Y X vac travel gt gt Y X http www pyramis gr package1 Y http geography int Egypt X http www pyramis gr package2 Y http geography int Egypt X http www travel_plan gr package2 Y http geography int Croatia X http www travel_plan gr package1 Y http geography int Italy Notice that the solutions obtained by global predicates are simply the union of the answers of each loaded rulebase where they are defined Thus interpretations of predicates may be distinct in distinct rulebases If a global interpretation is desired for some rulebase that rulebase must use the predicate besides defining it This fine grained control is very flexible and general 33 Coding complex rules Ruleb
42. ion explicitly the queried rulebase In the latter case the corresponding rulebases must be loaded The selected packages by Anne can be obtained by calling predicate test of testTravel If users wish to see all the entailed triples then they can enter the query testall Let s obtain the selected packages 34 mwebQuery Package Country Package ann choose trav package gt gt Country Package http www pyramis gr package1 Country http geography int Egypt Package http www travel_plan gr package2 Country http geography int Croatia no The first solution is obtained by the first condition captured by the first and second rules and the second solution is obtained from the second condition captured by the third rule The first package of Travel Plan is not selected because Italy is a European Union country and thus condition neg http geography int ltaly rdf type gt gt eu CountryEU fails 35 Inconsistent example This example can be found in directory USERDIR examples inconsistent and the rulebase files can be compiled by consulting mweb test Inconsistent and loaded with the command load A test can be performed by executing predicate test load test MWebWFS solutions neg http example orgZq X 8 http example3 org X b X c http example orgzp X X a X c naf http example orgZp X X b X c http example orgZp X
43. me or by recursively loading the rulebases listed in the rulebases uses declarations 17 The single rulebase loading command is mwebLoadModule RulebaseIRI while the recursive one is mwebLoadAllModules RulebaseIRI For instance the command mwebLoadModule http geography int loads the rulebase compiled in module file http963A962F962Fgeography962Eint pl Several dynamic predicates are asserted to XSB s database in order to hide from the user the internal names used by the MWeb compilation process as well as to support properly global predicates Users may unload explicitly modules generated from rulebases with the command mwebUnloadModule RulebaseIRI Users may load several modules by using command mwebLoadModules ListOfIRIs which loads each module appearing in the Prolog list ListOfIRIs It can also be used to load a single module This predicate calls mwebLoadModule 1 for each member of the list The command mwebLoadModules http geography int http europa eu loads the rulebases compiled in files http963A962F962Fgeography962Eint pl and http 3A 2F 2Feuropa 2Eeu pl Sometimes errors while loading modules leave the MWeb s internal database in an inconsistent state It is better that you start over again in a new instance of XSB after fixing any existing bugs or errors Finally mark that visible predicates without a rulebase list in the uses declaration import from all the loaded modules that
44. ned by the mwebModel Literal predicate However results must be interpreted carefully since as in the present example not all rulebases may have the same definition for global predicates For generating the same interpretation for global predicates in all rulebases these must be defined with the same mode and with the same context and used with the same mode in all rulebases 39 9 Current limitations and future developments For ease of implementation or more flexibility there are some differences to the theoretical MWeb framework which are collected next Users can define global predicates in non monotonic modes closed and normal This is forbidden in the MWeb theoretical framework since these are expected to be monotonic Users should use this at their own risk A warning message is printed The vocabulary of any rulebase is always the one obtained from all the loaded rulebases The MWeb ERDF theoretical framework obtains the vocabulary from the dependencies of a given rulebase For ease of implementation this has not been implemented but it is expected to be tackled in the near future Goals using vocabulary not defined in the loaded rulebases usually are false by default instead of raising any kind of runtime error Forms to circumvent this problem have been discussed in the examples Consistency checks are not performed automatically in MWebWFS The users must perform the checks explicitly A paraconsistent semantics is implemen
45. niou Carlos V Damasio A Principled Framework for Modular Web Rule Bases and its Semantics Procs of the 11th International Conference on Principles of Knowledge Representation and Reasoning KR 2008 pp 390 400 Australia September 2008 AAAI Press Anastasia Analyti Grigoris Antoniou Carlos V Damasio Gerd Wagner Extended RDF as a Semantic Foundation of Rule Markup Languages Journal of Artificial Intelligence Research JAIR 32 pp 37 94 2008 AAAI Press Carlos V Damasio Anastasia Analyti Grigoris Antoniou Gerd Wagner Supporting Open and Closed World Reasoning on the Web Procs of 4th Workshop on Principles and Practice of Semantic Web Reasoning PPSWR 2006 Budva Montenegro pp 149 163 June 2006 Springer Verlag 45
46. nt dependencies of the queried goals For 36 checking consistency under MWebWFS semantics on normal regime users can call mwebCheckConsistency mwebCheckConsistency Error XSB Runtime Unhandled Exception mweb Inconsistent modular rulebases It is also available the predicate mwebCheckConsistency Semantics Regime for checking general consistency under Semantics in mode Regime mwebCheckConsistency wfs d yes mwebCheckConsistency asp d yes mwebCheckConsistency asp n Error XSB Runtime Unhandled Exception mweb Inconsistent modular rulebases The results are expected since inconsistencies arise only on normal mode because of the rules for ex r 1 and ex q 1 Notice that in definite mode only ex q c is concluded under both semantics mwebQuery X ex q X 8 http example2 org wfs d mwebQuery X ex q X 8 http example2 org asp d X C no One of the interesting features of MWebWFS semantics is that it is able to identify which conclusions depend on contradiction Users can always check if some goal depends on contradiction by querying the goal and its weak negation If both succeed then the conclusion is dependent on contradiction This is illustrated quite well with the following queries mwebQuery X ex p X X a X C no mwebQuery X neg ex p X no mwebQuery X naf ex p X X b X C
47. o Country 1 from http geography int uses normal class mw Vocabulary from http geography int Some interesting queries are collected below the order of the answers does not matter Objective queries Default queries mwebQueryC mwebQueryC C http europa eu CountryEU C naf http europa eu CountryEU C C http geography int Austria C Rita C http geography int Greece C http geography int UK C http geography int Portugal C Anne C http geography int Canada no C Peter mwebQueryC C http geography int China neg http europa eu CountryEU CC C Boris C http geography int Egypt C http geography int Canada C http geography int Croatia C http geography int China C Vocabulary C http geography int Croatia C http geography int Egypt no mwebQueryC C naf neg http europa eu CountryEU C C Rita http geography int Portugal http geography int UK Anne http geography int Greece Peter Boris http geography int Austria Vocabulary C YOonCcncnn0n00 I 23 o Since an explicit context predicate was provided then the closed world assumptions are done with respect to the answers of this predicate thus limiting the things that are known to not being European countries With negation as failure more answers are obtained but are non monotonic later on we might
48. olog module will be generated with the compiled code The name of the Prolog file is obtained from the rulebase declaration in the interface source file The Prolog file has pl extension and filename obtained by escaping all chars except for letters digits HYPHEN MINUS and LOW LINE ofthe rulebase IRI A rulebase with source files geo mw and geo rb can be compiled with the command mwebCompileModule geo generating the file http963A962F962Fgeography962Eint pl if the rulebase declaration in geo rw is rulebase http geography int Users can also organize the rulebases by using the encoded name The previous rulebase could be encoded in the following interface and logic program files http 3A 2F 2Fgeography 2Eint mw http 3A 2F 2Fgeography 2Eint rb respectively and the compilation of the rulebase can be done with the command mwebCompileModule http geography int The binary predicate mwebCompileModule InterfaceFile RulesFile allows for the compilation from explicitly provided interface and logic program files Currently all the files should be in XSB s default search path Output of the compilation process is very verbose and usually some warnings might be printed If the rulebase is not legal then an error is thrown All these predicates compile immediately the generated XSB s Prolog file implementing MWeb s semantics Loading After compiling the rulebase each module can be loaded one at a ti
49. olver is called to handle the query complexity co NP complete The most general version is mwebQuery Vars Goal Semantics Regime which allows the user to use a particular MWeb regime d for definite o for open c for closed n for normal which is the default one All the variants of the querying predicates are further explored in the Examples section 21 8 Examples In this section we provide and explain the main features of the MWeb framework by three extended examples One of the examples is devoted to explain the several MWeb constructs and regime modes as well as practical differences among them security example The second example illustrates the support of ERDF travel example The remaining example illustrates inconsistency handling and global predicates in MWeb inconsistent example Security Example This example can be found in directory USERDIR examples security and the rulebase files can be compiled and loaded by consulting mweb testSecurity and then calling the predicate load A test can be performed by executing predicate test load test MWebWFS solutions Anne MWebAS solutions Boris Anne yes The example file also declares the prefixes used in the following examples First queries The first rulebase defines World countries via predicate http geography int Country whose instances are positively closed In practice this means that developers are stating that the li
50. on The import directive is recursively substituted by the contents of Filename The syntax of rules is presented and explained next Table 6 Syntax of MWeb logic rules Name Syntax Comment Rule Implies Fact Implies Head Body A rule if Body then Head Head must be an atom or the strong negation of an atom while Body is an arbitrary formula Fact Head Abbreviation for a rule with true body And Conji ConjN A conjunction separator is comma Or Disj1 DisjN A disjunction separator is semi colon Qualified Default 8e RulebaseIRI A call to Default literal in RulebaseIRI Default naf Objective Objective Weakly nonmonotonic negated Objective literal Naf is the preferred syntax Objective neg Atom Atom Strongly negated Atom monotonic Neg is the preferred syntax should be avoided Atom C Prefix Name An optionally prefixed Name with an optional C C Termi TermN list of term arguments Term Const Var A term is either a constant a variable or a C Prefix Name complex term C C Termi n Term Const A XSB Prolog constant or a typed literal PROLOGCHAR CURIE Currently no syntax checking of typed literals is performed Var 2 Name Differently from Prolog a variable must be 2 _ Name prefixed with a question mark The name of the variable can be an arbitra
51. ple org p c naf neg http example org q a http example org q c http example org r c neg http example org r c naf http example org q a naf http example org q b naf http example org r a naf http example org r b naf http example org r c naf neg http example org q a naf neg http example org q b naf neg http example org q c naf neg http example org r a naf neg http example org r b naf neg http example org r c http example org q a neg http example org q b neg http example org q c naf http example org q b naf http example org q c naf neg http example org q a naf neg http example org q c These models clearly show that rulebase http example3 org is consistent rulebase http example2 org is inconsistent because of predicate r defined in normal model but consistent in definite mode since q is defined in this rulebase definite and rulebase http example1 org is inconsistent because it uses the global predicate q which is inconsistent because of conflicting definitions between the other two rulebases As explained before predicate p in the first rulebase depends on q and thus has an instance inconsistent This example also shows how users can share the global definitions of predicates they must use the predicate from everywhere besides declaring it global The global model of the loaded rulebases can also be obtai
52. r friendly differences It is expected that other input formats to be supported in the future e g RIF N3 Jena Prolog etc The MWeb Interface The syntax of the MWeb interface is given by the following pattern where terminals are quoted in bold and non terminals in italic Notice that the several language constructs are aligned with RIF syntax in order to foster future integration All statements end with a dot and terminals can be separated with whitespace Comments can be put inside pairs or be line comments starting with Table 1 MWeb interface file constructs rulebase IRIRef base IRIRef prefix Name IRIRef Name IRIRef C importC FileName interface gt gt gt C vocabulary Const C Const DefinesDecl UsesDecl The MWeb interface starts with a mandatory rulebase declaration providing its unique identifier For maintaining compatibility with Prolog it is allowed to use an IRI reference as module identifier instead of restricting exclusively to Absolute IRIs For uniformity IRI references should be put inside quotes An optional Base IRIRef can be specified to resolve Compact URIs for the default namespace The optional declaration of other namespace prefixes and its association with IRIRefs follow immediately Notice that sev
53. roperty rdfs domain gt gt rdfs Resource rdfs range gt gt rdfs Resource External atom atom X prolog External atom atom concat rdf _ N X prolog External atom is number atom N prolog rdfs ContainerMembershipProperty rdfs subClassOf gt gt rdf Property rdfs isDefinedBy rdfs subPropertyOf gt gt rdfs seeAlso rdf XMLLiteral rdf type gt gt rdfs Datatype rdf XMLLiteral rdfs subClassOf gt gt rdfs Literal rdfs Datatype rdfs subClassOf gt gt rdfs Class The Extended Resource Description Framework introduces the notions of total and closed class as well as total and closed property and a mechanism to express complementary properties Totalness is captured by declaring the class and property having rdf type erdf TotalClass and erdf TotalProperty classes respectively For declaring closed classes and properties the erdf PositivelyClosedClass erdf NegativelyClosedClass erdf PositivelyClosedProperty and erdf NegativelyClosedProperty can be used with the expected meaning The semantics of these ERDF constructs is specified by normal rules and grounding of variables is made in the code by using the instances of class mw Vocabulary 14 ERDF s MWeb interface erdf mw rulebase http erdf org prefix erdf http erdf org import rdfs mw interface defines internal normal class erdf TotalClass defines internal normal class erdf Po
54. rules A query using a constant France not in the vocabulary has identical behaviour The remaining distinctive mode to analyse is the open entailment regime explained next Objective queries on regime o Default queries on regime o mwebQueryC X mwebQueryC X geo Country X wfs o naf geo Country X wfs o X http geography int Portugal no X http geography int Greece mwebQueryC X X http geography int Canada naf neg geo Country X wfs o X http geography int China X http geography int Egypt X http geography int Portugal X http geography int Croatia X http geography int Greece X http geography int Austria X http geography int Canada X http geography int China no X http geography int Egypt mwebQueryC X X http geography int Croatia neg geo Country X wfs o X http geography int Austria no no mwebQuery mwebQuery geo Country France wfs o naf geo Country France wfs o no yes mwebQuery mwebQuery neg geo Country France wfs o naf neg geo Country France wfs o no yes Regarding objective queries the results are as before The default queries are very interesting to explain Roughly all the things that are not entailed by the objective part are undefined note the symmetries This mode is monotonic for objective queries and
55. ry name i e start with lower case or even be a Prolog atom _ is an anonymous variable Name A name can be an identifier starting with a letter lower or upper case separated with underscores or an arbitrary UTF 8 string inside quotes The special predicate Domain ListOfVars_ can be used in bodies of rules to instantiate unbound variables with all the vocabulary available from loaded rulebases This is particularly useful when using rules with weak negations in order to instantiate the corresponding variables otherwise floundering problems may occur The MWebWFS and MWebAS semantics Two semantics are defined for the MWeb framework and selected at query time The MWebWKES is a semantics based on Paraconsistent Well fouded Semantics with Explicit negation Ground queries can be evaluated in polynomial time on the size of the instantiated rulebase and existence of a single model is guaranteed Users can check consistency of a query by checking if L and naf L are simultaneously true If so the query is itself contradictory and thus neg L is also true or dependent on contradiction This semantics is the best tractable approximation to MWebAS currently known No consistency checks are done for this semantics The MWebAS semantics is the semantics based on Answer Set semantics and consequently has the benefits and disadvantages of the latter Consistency checks are done automatically for this semantics and some rulebases may not hav
56. ry naf X rfds subClassOf gt gt Y Y rdfs subClassOf Z Total and closed classes properties The rulebase http europa eu defines an open and incomplete list of European Union countries The open world assumption is declared by the statement that http europa eu CountryEU is an erdf TotalClass A class closed world assumption can be declared in a similar manner by erdf PositivelyClosedClass and erdf NegativelyClosedClass as shown in the previous geordf rb MWeb logic program 31 Europa s MWeb interface europardf mw Europa s MWeb logic program europardf rb rulebase http europa eu base http europa eu prefix eu http europa eu geo http geography int import erdf mw interface defines local normal class eu CountryEU uses normal class geo Country from http geography int uses normal class mw Vocabulary from http geography int import erdf rb rulebase eu CountryEU rdf type gt gt erdf TotalClass geo Italy rdf type gt gt eu CountryEU geo Greece rdf type gt gt eu CountryEU To check that the European Union class is really open users can perform the following queries to contrast the different behaviour of European countries according to http europa eu rulebase and http geography int Checking open class Checking closed class mwebQuery X X amp eu CountryEU X
57. s and believe to be countries naf neg construction on the right appears the entities that are not countries neg and believed to not being countries naf Since the developer did not define a context predicate for geo Country the closed world assumption is performed with respect to instances of mw Vocabulary thus constants Anne Boris Peter and Rita appear elsewhere Also notice the use of the base directive to simplify the encoding of the rulebase It is instructive to query with a new constant not in the vocabulary to observe the different behaviour Before adding geo UK to vocabulary After adding geo UK to vocabulary vocabulary geo UK yes mwebQuery geo Country geo UK 5 mwebQuery geo Country geo UK no no mwebQuery neg geo Country geo UK mwebQuery neg geo Country geo UK 5 no yes mwebQuery naf geo Country geo UK mwebQuery naf geo Country geo UK 5 yes mwebQueryC naf neg geo Country geo UK yes mwebQuery naf neg geo Country geo UK 5 yes no Since http geography int UK is not listed in the rulebase it does not hold http geography int ZCountry http geography intZUK Because the constant http geography int UK does not belong to the vocabulary then closed world assumption does not apply and the query neg http geography int Country http geography
58. s for neg gov Enter 1 and predicate is defined in normal mode there is no way to conclude explicitly false knowledge However we are able to conclude that the system believes that Peter should not enter the country because he is a suspect 28 Regarding Rita we cannot conclude anything since she might be a citizen of an European country or not Therefore she might be allowed to enter in some models and refused to enter in other models where she has non European nationality Since reasoning in MWebWFS considers only one model reasoning is polynomial on the size of the grounded rulebase In the worst case reasoning in MWebAS is co NP complete intractable since it might be necessary to consider an exponential number of possible models 29 Travel Example The travel example can be found in directory USERDIR examples travel and the rulebase files can be compiled and loaded by consulting mweb testTravel and then calling the predicate load Since this example can consume quite a large amount of memory with MWebAS semantics users are advised to invoke XSB with parameter m 50000 A simple test can be performed by executing predicate test load test MWebWFS solutions Chttp ww travel_plan gr package2 http geography int Croatia Chttp ww pyramis gr packagel http geography int Egypt MWebAS solutions Chttp ww travel_plan gr package2 http geography int Croatia Chttp ww pyramis gr package1l h
59. s wfs or asp and Regime values d o c or n Notice that the rulebases might be inconsistent in one regime and consistent in other regimes mwebCheckConsistency The same as mwebCheckConsistency wfs n 43 Model Construction mwebModel Rulebase Semantics Regime PredInd Literal Backtracks over all literals true in Rulebase constructed from PredInd PredName Arity under Semantics with mode Regime If Rulebase is a variable then it returns literals true in the global interpretation If PredInd is a variable then it is returned all literals true of defined predicates in the provided rulebase mwebModel Literal The same as mwebModel _ wfs n _ Literal mwebModel Rulebase Literal The same as mwebModel Rulebase wfs n _ Literal mwebModel Rulebase Semantics Literal The same as mwebModel Rulebase Semantics n _ Literal mwebModel Rulebase Semantics Regime Literal The same as mwebModel Rulebase Semantics Regime _ Literal 44 11 Readings Anastasia Analyti Grigoris Antoniou Carlos V Damasio MWeb A Principled Framework for Modular Web Rule Bases and its Semantics Submitted for publication 2010 Anastasia Analyti Grigoris Antoniou Carlos V Damasio A Formal Theory for Modular ERDF Ontologies Proceedings of Third International Conference Web Reasoning and Rule Systems RR 2009 pp 212 226 Chantilly VA USA October 2009 Springer Verlag Anastasia Analyti Grigoris Anto
60. sitivelyClosedClass defines internal normal class erdf NegativelyClosedClass defines internal normal class erdf TotalProperty defines internal normal class erdf PositivelyClosedProperty defines internal normal class erdf NegativelyClosedProperty defines internal normal property erdf complementOf ERDF s MWeb logic program erdf rb import rdfs rb rulebase 96 Equivalence of neg and neg rdf type RIF compatibility neg X Y neg X rdf type gt gt Y neg X rdf type gt gt Y neg X Y 96 Inclusion of negative subclass extension neg X rdfs subClassOf gt gt Y neg X Y 96 ERDF extra rule for obtaining RDF properties Z rdf type gt gt rdf Property neg Z gt gt 96 ERDF RDFS negative extension rules neg Z rdf type gt gt X X rdfs subClassOf gt gt Y neg Z rdf type gt gt Y neg Z1 X gt gt Z2 X rdfs subPropertyOf gt gt Y neg Z1 Y gt gt Z2 96 ERDF specific rules 96 Closed classes and properties neg Z rdf type gt gt X X rdf type gt gt erdf PositivelyClosedClass X rdf type gt gt erdf TotalClass Z tt mw Vocabulary naf Z rdf type gt gt X Z rdf type gt gt X X rdf type gt gt erdf NegativelyClosedClass X rdf type gt gt erdf TotalClass Z mw Vocabulary naf neg Z rdf type gt gt X neg Z1
61. st is complete not true as readers can manifestly check Since the predicate is defined local it cannot be defined local or global in a different rulebase Geo s MWeb interface geo mw RIF s MWeb logic program geo rb rulebase http geography int Country Austria base http geography int Country Canada Country China defines local closed Country 1 Country Croatia defines global normal class mw Vocabulary Country Greece Country Egypt uses normal class mw Vocabulary Country Portugal Let s check what consequences we can extract from the above rulebase where results can be found below assuming that mwebQuery geo Country X mwebQuery neg geo Country X mwebQuery C X naf neg geo Country OD mwebQuery C X naf geo Country X X http geography int Portugal X Rita X http geography int Greece X Anne 22 X http geography intZCanada X Peter X http geography int China X Boris X http geography int Egypt X Vocabulary X http geography int Croatia X http geography int Austria Since the predicate is defined closed there are no differences between objective queries and default queries because the vocabulary includes all defined constants exported by modules because of the uses normal class mw Vocabulary declaration On the left appears the list of known countrie
62. ted with a better behaviour in face of contradiction than the MWebWFS theoretical framework The current implementation has several limitations which are briefly described There is no means for using the local rulebase vocabulary as context for open and closed world assumptions More complex vocabulary constant using complex terms is necessary currently is limited to constants Subsumptive tabling is much better in terms of memory consumption than variant tabling in particular for RDF reasoning However the current implementation is not handling it appropriately because of some cuts in the generated code Alternative coding must be devised There is no tabling control by the user therefore in some situations we are using more memory than the one strictly necessary This has negative performance impacts A unique general program transformation is used both for MWebWFS and MWebAS semantics For the case of consistent theories the transformed program can be simplified reducing tabling Elementary support of RIF and XML Schema datatypes just recognizing terms of the form Literal IRI The command level query syntax is different from the one used in rulebases which might introduce some confusion to non expert users Restricted number of Prolog external predicates is supported Better integration is necessary The next developments of the MWeb framework will include Support of RIF and XML Schema datatypes Direct translation of Exten
63. tomic symbol defined by Prolog syntax Name is an alphanumeric string of literals starting in lower or upper case while Atom matches an optionally prefixed logical atom with arguments Here users can use names starting with upper case but need to prefix variables with a question mark symbol These are detailed in Table 6 Table 3 Summary syntax and meaning of the defines declaration defines ScopeDecl global The predicates can be defined in several rulebases local The predicates can be defined only in a single rulebase internal The predicates are invisible to other rulebases RegimePred definite The rules for the predicates are monotonic Non weakly negated conclusions are monotonic Only strong negation can be used in the defining rules and normal predicates are forbidden Similar to Horn programs but with strong negation open The rules for the predicates are monotonic with open world assumption Non weakly negated conclusions are monotonic Only strong negation can be used in the defining rules and normal predicates are forbidden Similar to Horn programs but with strong negation allowed with open world assumption closed The rules for the predicates are associated with a positive or negative closed world assumption depending on the keyword neg in PredicateList Conclusions are non monotonic Only strong negation can be used in the defining rules and normal predicates are forb
64. ttp geography int Egypt yes A more extensive test can be executed by calling predicate testall dumping the list of triples Subject Property Object which can be concluded from the example under MWebWFS and MWebDAS semantics Users can evidence the different response times of both semantics MWebWPFS is faster than MWebAS Using ERDF syntax and semantics We start again by defining a rulebase with world and European countries This time we use the ERDF support of the MWeb framework which introduces new syntax for simplifying writing of rulebases on top of the Extended Resource Description Framework Geo s RDF MWeb interface geordf mw Geo s RDF MWeb logic program geordf rb rulebase http geography int import erdf rb rulebase base http geography int geo Europ Country rdf type gt gt erdf PositivelyClosedClass prefix geo http geography int geo Europ Country rdfs subClassOf gt gt Country import erdf mw interface geo Egypt rdf type gt gt geo Country geo Egypt geo capital gt gt geo Cairo defines local normal class geo Country defines local normal class geo Europ_Country geo ltaly rdf type gt gt geo Europ Country defines local normal property geo capital geo capital gt gt geo Rome geo Croatia rdf type gt gt geo Europ_Country geo capital gt gt geo Zagreb The rulebase defines properties and class
65. ttp ww travel_plan gr package1 20 no Obtain the things X which are not RDFS classes mwebQueryC X naf X rdfs Class X http www w3 0rg 2000 01 rdf schemaz comment X http www travel org visit Cthe list continues The following queries illustrate the flexibility of the system introduced by the two negations and its use Obtain the European countries mwebQuery C X C X geo Europ Country gt lt ll http geography int Croatia X http geography int Italy Obtain the non European countries mwebQueryC X C X geo Country neg X geo Europ Country X http geography int Egypt Obtain the entities X believed not to be European countries mwebQueryC X naf X geo Europ Country X http www w3 0rg 2000 01 rdf schemazicomment X http www travel org visit Cthe list continues More advanced uses of the querying interface may use the other two variants of the mwebQuery predicate The call mwebQuery Vars Goal Semantics executes Goal with free variables Vars under Semantics in normal mode Semantics is either the constant w s the default based on Well founded Semantics MWebWFS or asp the answer set based semantics MWebAS Notice that the asp version requires all variables to be grounded in the query so all variables in the query must appear in the Vars list and can be very inefficient since an answer set s
66. ules Syntactically the MWeb parser supports RIF frames molecules of the form 0 A1 gt gt V1 An gt gt Vn which internally are translated into a conjunction mark the order of arguments gt A1 0 V1 gt An 0 Vn The other binary RIF predicates equality member Isa and subclass have the exact syntax of RIF The semantics of these predicates are provided by the following MWeb rulebase RIF s MWeb interface rif mw RIF s MWeb logic program rif rb rulebase http www w3 org 2007 rif 96 RIF member relation extended to handle strong negation prefix rif http www w3 org 2007 rif 20 4 CL 20 amp SCL SCL CL neg 0 SCL neg 0 CL SCL CL defines internal normal name 2 defines internal normal name 2 RIF subclass relation No rule needed for strong negation defines internal normal name t 2 C1 4HE C3 C1 C2 C2 C3 defines internal normal name gt 3 RIF partial equality theory defines global normal class mw Vocabulary T T T mw Vocabulary T1 T2 T2 T1 T1 T3 T1 T2 T2 T3 neg T1 T2 neg T2 T1 neg T1 T3 T1 T2 neg T2 T3 96 RIF frames obtained by equality reasoning 0 P gt gt V 01 P gt gt V 0 O1 0 P gt gt V 0 P1 gt gt V P P1 0 P gt gt V 0 P gt gt
67. unintended interactions of loaded modules and trivialization because of inconsistent rulebases as illustrated previously For simplifying the construction of full models of rulebases the predicate mwebModel Rulebase Literal and its variants can be used to backtrack over all Literals true in Rulebase These can be collected with setof or findall setof L mwebModel http example3 org L Model L h140 http example org q a naf http example org q Vocabulary naf http example org q b naf http example org q c naf neg http example org q Vocabulary naf neg http example org q a neg http example org q b neg http example org q c 38 no The previous command obtains all the literals L true in rulebase http example3 org under semantics MWebWFS on normal mode and collects them in list Model The models of the remaining rulebases can be obtained similarly and are shown in the next table ignoring the Vocabulary constant Rulebase http example1 org Rulebase http example2 org Rulebase http example3 org http example org p a http example org p c http example org q a http example org q c neg http example org q b neg http example org q c naf http example org p b naf http example org p c naf http example org q b naf http example org q c naf neg http example org p a naf neg http example org p b naf neg http exam
68. ways refine existing predicates by using it in definite mode and defining it internal on the wished regime extra facts and rules can be defined internally in the rulebase see sec citizenOf 2 predicate A predicate defined in normal mode can have occurrences of weak negation in the bodies of its rules as the gov Enter 1 predicate shows A rulebase can query a specific rulebase by using the operator This last rulebase also helps to understand the differences between MWebWFS and MWebAS semantics Let s check which persons are allowed to enter the country Answers under MWebWFS semantics Answers under MWebAS semantics mwebQuery P http gov countrystEnter P wfs P Anne no mwebQuery P neg http gov country Enter P no mwebQuery P naf http gov country Enter P P Peter no mwebQuery P naf neg http gov countrystEnter P P Rita P http geography int Portugal P http geography int UK P Anne P http geography int Greece P http geography int Canada P Peter P http geography int China P Boris P http geography int Egypt P http geography int Croatia P http geography int Austria P Vocabulary no mwebQuery P http gov country Enter P asp P Anne P Boris no mwebQuery P neg http gov country tEnter P asp no mwebQuery P naf http gov
69. y X wfs d no mwebQueryC geo Country France wfs d no mwebQueryC neg geo Country France wfs d no mwebQueryC X naf geo Country X wfs d Rita Anne Peter Boris http geography int UK Vocabulary X X X X xXx mwebQueryC X naf neg geo Country X wfs d Rita http geography int Portugal http geography int UK Anne http geography intzGreece http geography int Canada Peter http geography int China Boris http geography int Egypt http geography int Croatia http geography int Austria Vocabulary gt lt gt lt X X X OK X X X xX OK xXx ll no mwebQueryC naf geo Country France wfs o yes mwebQueryC 1 naf neg geo Country France wfs o yes As expected we obtain the list of answers of registered countries Notice that the default query naf geo Country X obtains the complementary solutions of the registered vocabulary Since no rules for neg geo Country X are present in the logic program the query fails with no answers and thus all the constants in the vocabulary are answers to the default query naf neg geo Country X It can be shown that objective answers are monotonic on the extension of the rulebase while default ones are non monotonic This 24 justifies the restriction to forbid the use of weak negation in the bodies of

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