Notes

Outline

Semantic Web and Natural Semantics Adrian Pop IDA/PELAB adrpo@ida.liu.se

Outline Semantic Web Natural Semantics Relational Meta-Language (RML) Semantic Web Layers Tools Ontology Checkers Checking Semantics of Websites Conclusions

Semantic Web The information in the current web: has meaning for human only is not machine processable Semantic Web brings: semi-structured information means to add structure (semantics/constrains) on data, with the use of: languages: XML, XMLSchema, RDF, RDFS, DAML+OIL, OWL

Natural Semantics Based on Gordon Plotkin's Structural Operational Semantics (SOS) Gentzen's Sequent Calculus for Natural Deduction. "Natural Semantics" (NS) term by Gilles Kahn formalism for specifications of: type systems programming languages

Natural Semantics - Syntax Hi are hypotheses (environments with bindings) Ti are terms (pieces of abstract syntax) Ri are results (types, run-time values, changed environments) Hj |- Tj : Rj are sequents Premises or preconditions are above the line Conclusion is below the line Condition on the side if exists must be satisfied

Natural Semantics vs RML RML has the same visual syntax as NS rule   RelName1(H1,T1) => R1 & ...        RelNameN(Hn,Tn) => Rn &        <cond>        ------------------------------        RelName(H, T) => R

Natural Semantics vs RML rules and propositions are grouped into relations relation negate: bool => bool =   axiom negate true => false   axiom negate false => true end axioms are rules with no premises axiom negate true => false rule        ---------------------        negate true => false

RML datatypes, types, tuples datatype declaration   datatype Exp = INT of int                 | NEG of Exp                 | ADD of Exp*Exp type declaration (aliases)    type Constant = int    type Identifier = string tuples declaration    type Point = int * int    type Bag = string * int * Exp

RML example: the Exp language Abstract syntax datatype Exp = INTconst of int              | PLUSop of Exp * Exp              | SUBop of Exp * Exp              | MULop of Exp * Exp              | DIVop of Exp * Exp              | NEGop of Exp  Exp: 10 – 12/3

RML example: the Exp language Relation eval relation eval: Exp => int =  axiom eval(INTconst(ival)) => ival  rule eval(e1) => v1 & eval(e2) => v2 & int_add(v1,v2) => v3       ------------------------------------------------------       eval (PLUSop(e1,e2)) => v3  rule eval(e1) => v1 & eval(e2) => v2 & int_sub(v1,v2) => v3       -----------------------------------------------------       eval (SUBop(e1,e2)) => v3  rule eval(e1) => v1 & eval(e2) => v2 & int_mul(v1,v2) => v3       -----------------------------------------------------       eval (MULop(e1,e2)) => v3  rule eval(e1) => v1 & eval(e2) => v2 & int_div(v1,v2) => v3       -----------------------------------------------------       eval (DIVop(e1,e2)) => v3  rule eval(e) => v1 & int_neg(v1) => v2       -----------------------------------------------------       eval (NEGop(e)) => v2 end

RML overview

RML Tools for Semantic Web Layer RML tools

Ontology Checkers Checkers

Ontology Checkers – directions & problems Directions building the DAML2RML translator finding a mapping between DAML and RML can be problematic Problems RML is not user friendly The internal  RML library is not very powerful An RML debugger exists but has to be improved

Related Work - Checking Semantics of Websites Thierry Despeyroux - Brigitte Trousse http://www-rocq.inria.fr/~tdespeyr/papers/riao2000-2 Applications of NS to Markup Language Based Documents specifying the semantics of new XML languages with Natural Semantics translation from DTD to a form of Abstract Syntax Tree Maintaining of Web Sites – Examples Specifying a Thematic Directory Specifying the Coherence of an Institutional Site

Future Work Applying RML to check ontologies RML vs RuleML (differences & similarities)

Conclusions Natural Semantics is a powerful formalism to used to specify semantics of programming languages RML (Relational Meta-Language) can generate executabile specifications Building a paralel between programming languages and Semantic Web languages one could find places where RML can prove useful.