1. Reasoning Web 2007 summer school Ondřej Šváb (UEP)

2. Summer school 3rd summer school of Reasoning Web Malta, Lisbon, Dresden Around 40 participants (canditates of PhD), Many contributors to tutorials LNCS Proceeding –¨Fundamentals of Reasoning and Reasoning Languages¨ query paradigms, declarative semantics, complexity and expressive power, procedural semantics, implementations, optimisation, and many more.. –¨Rules and Policies¨ –¨Applications of Semantic Web Reasoning¨ Supported by the European Network of Excellence (REWERSE)

3. ¨Fundamentals of Reasoning and Reasoning Languages¨ Francois Bry et al. Foundations of logic –First-Order Predicate Logic (syntax, Tarski Model Theory, Herbrand Model Theory) –Tarski inadequacies Unique name assumption Terms as compound data structures Closed world assumption Disregard infinite models

4. ¨Fundamentals of Reasoning and Reasoning Languages¨ Francois Bry et al. Foundations of logic –First-Order Predicate Logic (syntax, Tarski Model Theory, Herbrand Model Theory) –Tarski inadequacies Unique name assumption (Herbrand models) Terms as compound data structures (Herbrand m.) Closed world assumption (minimal Herbrand m.) Disregard infinite models (finite model theory)

6. Declarative semantics Minimal Model Semantics of Definite Rules (Herbrand models) Fixpoint Semantics of Positive Definite Rules Declarative Semantics of Rules with Negation (CWA) …

7. Operational semantics Naive evaluation of datalog programs –Extensional predicates are mapped to intensional predicates SLD-resolution:basic backward chaining –SLD=Selected Literal Definite Clause –SLD-tree –disadantage: generally infinite OLDT-resolution –tabling – store intermediate results for later usage –Better performance, but still non-deterministic alg.

8. Operational Semantics The magic templates transformation alg. –Both, goal-directed search as well as forward chaining –2 steps: Transformation into adorned version (sip) Rewriting adorned version into set of rules that can be efficiently evaluated

9. Operational Semantics Rete algorithm –By Charles Forgy in 1974 –alg. For inference engines of rule based ES –eg. in Clips, JRules, OPS5 –Two types of memories: Production memory (rules) Working memory (ground facts, implied facts) Processing of rules in Rete network (four types of nodes) –Forward Chaining, sharing information

10. Rete algorithm

11. Complexity and Expressive Power of Logic Programming Formalisms Nice introduction into complexity (turing machine, complexity classes) and much more

12. Reasoning in Description Logics by Ulrike Sattler The logic basis for OWL flavours ‘common’ reasoning in service based systems for ontology developing –The computation of the taxonomy –Checking the satisfiability, consistency –Satisfiability and subsumption wrt. TBox –Consistency and instance wrt. ABox Others (non-standard inferences services): –Debugging support to explain unintended specialisation links –Extraction of sub-ontology describing the concept –Find (the most specific) generalisation –Find approximation of a concept

13. DLs Syntax, semantics, reasoning Many exercises: interpretations, tableaux algorithm (satisfiability of concept) –Pellet, RacerPro, FaCT++ Other reasoning approaches: –Disjunctive datalog engine (KAON2) –Technique from deductive databases –Rule-based (rule engine) (OWLIM), costly materialization strategy DLs and rules (combination) –Reasons for rules, p. 177 Adding non-monotonicity (rules have CWA, negation as failure) Generally increasing DLs’ expressive power

14. ¨Rules and Policies¨ Reactive rules on the Web –Rule based reactive systems on the web –Two approaches Event-Condition-Action rules –ON event IF condition DO action Production rules –WHEN condition DO action –Examples of application scenarios –Examples of languages –Differences…

15. ¨Rules and Policies¨ Rule-based policies –Security policies, trust mng policies, business rules,… –Requirements for a policy framework –Examples of languages KAOS and Protune

16. Rule Interchange on the Web Standardisation effort of RIF WG within W3C Not trivial task – different current rule languages (diverse syntax and semantics) –Deduction, normative, reactive rules So far RIF WG –Uses cases and requirements (implementability, semantic precision, extensible format, translators, standard components)

17. RIF RIF core – Horn rules RIF dialects - extensions

18. ¨Applications of Semantic Web Reasoning¨ The contradiction of Web and Reasoning Reasoning in Semantic Wikis –Reasoning for enhancing browsing, querying, editing, validating –Wikis for semantic data (collaborative ontology editors) –Semantic data for wikis (simplifying maintenance, retrieval,…)

19. Semantic Media Wiki Extension of MediaWiki Many ABox statements, shallow TBox Annotations made by people via a special markup (categories, relations, attributes)

20. IkeWiki In contrast to SMW, preloaded ontologies „restrive approach“ wrt. Annotation Reasoning – subclass and type inference

21. Examples of reasoning now Displaying and browsing wiki contents –Graphical visualisation, … Editing support –suitable properties (domain), values wrt. Consistency Validating against background knowledge

22. SMW – complex inferencing? Challenges: –maintaining ontologies in wikis (axioms vs. articles), higher expressivity –Performance – semantic query answering for large audience (semantic Wikipedia) –Usability – improved visual interfaces –Reasoning about context (suitable diagram) –Planning support (resource planning, appropriate date and people) – robustness

23. ¨Applications of Semantic Web Reasoning¨ Reasoning in Semantic Wikis (AIFB,Salzburg r.) –Not much reasoning, ideas Semantic Web Service Discovery (SAP r.) –Subsumption, request, offer Intergator – information retrieval mng system –GATE, Jena, Lucene Knowledge based search technologies –Biomedical literature, www.gopubmed.orgwww.gopubmed.org –Searching by browsing over structural results