Data Types(2) o AA-notation indicates the type of a literal In practice, the most widely used data typing scheme will be the one by xml schema But the use of any externally defined data typing scheme is allowed in rdf documents o XML Schema predefines a large range of data types E.g. Booleans, integers, floating-point numbers times dates. etc 21 Chapter 3 A Semantic Web primer
Chapter 3 A Semantic Web Primer 21 Data Types (2) ⚫ ^^-notation indicates the type of a literal ⚫ In practice, the most widely used data typing scheme will be the one by XML Schema – But the use of any externally defined data typing scheme is allowed in RDF documents ⚫ XML Schema predefines a large range of data types – E.g. Booleans, integers, floating-point numbers, times, dates, etc
A Critical view of rdf Binary Predicates o RDF uses only binary properties This is a restriction because often we use predicates with more than 2 arguments But binary predicates can simulate these EXample: referee(X,Y, 2) x is the referee in a chess game between players Y and z 22 Chapter 3 A Semantic Web primer
Chapter 3 A Semantic Web Primer 22 A Critical View of RDF: Binary Predicates ⚫ RDF uses only binary properties – This is a restriction because often we use predicates with more than 2 arguments – But binary predicates can simulate these ⚫ Example: referee(X,Y,Z) – X is the referee in a chess game between players Y and Z
A Critical view of rdf Binary Predicates(2) ● We introduce a new auxillary resource chessGame the binary predicates ref, player1, and player2 o We can represent referee(X,Y, z)as referee player chessGame →◎ player2 ② 23 Chapter 3 A Semantic Web primer
Chapter 3 A Semantic Web Primer 23 A Critical View of RDF: Binary Predicates (2) ⚫ We introduce: – a new auxiliary resource chessGame – the binary predicates ref, player1, and player2 ⚫ We can represent referee(X,Y,Z) as:
A Critical View of RDF: Properties o Properties are special kinds of resources Properties can be used as the object in an object-attribute-value triple(statement) They are defined independent of resources This possibility offers flexibility But it is unusual for modelling languages and oo programming languages It can be confusing for modellers 24 Chapter 3 A Semantic Web primer
Chapter 3 A Semantic Web Primer 24 A Critical View of RDF: Properties ⚫ Properties are special kinds of resources – Properties can be used as the object in an object-attribute-value triple (statement) – They are defined independent of resources ⚫ This possibility offers flexibility ⚫ But it is unusual for modelling languages and OO programming languages ⚫ It can be confusing for modellers
A Critical view of rdf reification e The reification mechanism is quite powerful It appears misplaced in a simple language like RDF Making statements about statements introduces a level of complexity that is not necessary for a basic layer of the Semantic Web Instead, it would have appeared more natural to include it in more powerful layers, which provide richer representational capabilities 25 Chapter 3 A Semantic Web primer
Chapter 3 A Semantic Web Primer 25 A Critical View of RDF: Reification ⚫ The reification mechanism is quite powerful ⚫ It appears misplaced in a simple language like RDF ⚫ Making statements about statements introduces a level of complexity that is not necessary for a basic layer of the Semantic Web ⚫ Instead, it would have appeared more natural to include it in more powerful layers, which provide richer representational capabilities