Comparison of data facilitiesRelational XML Web

Repn. 2-d array tree globally accessable pages

Data typing SQL, vendor extension

XSchema browser conventions: links, images, script, …

Relations keys: foreign primary

IDREF, XPointer, XLink

href

Namespace data dictionary: table, field names

xmlns URN (uniform resource name)

Schema relational schema XSchema XHTML, plus good luck.

Activity embedded SQL triggers (SQL99)

PI

external application

scripting

Integrity Relational integrity enforced

Validation voluntary browsers mostly ignore.

Semantic Web

• See Scientific American article

• How to express intended meaning of data

• Directed graph represented as a triples

• (resource,predicate (property) ,object)– (CS639, Teacher, "Robert A. Morris")

• Resource must have a URI

CS639 Robert A. Morris

Teacher

RDF

<rdf:Description about="http://www.cs.umb.edu/Programs/grad_Course.html#CS639">

<Course:Teacher>Robert A. Morris</Course:Teacher></rdf:Description>

or

<rdf:Description about="http://www.cs.umb.edu/Programs/grad_Course.html#CS639"

Course:Teacher="Robert A. Morris"/ ></rdf:Description>

Latter form doesn't support more structure for Teacher

Course should refer to an XSchema

RDF

http://…/gradCourse/#639

Robert A. Morris

Name

S/3/075Office

http://…/~ram

S/2/065

Teacher

Room

RDF

<rdf:Description about="http://www.cs.umb.edu/Programs/grad_Course.html#CS639">

<Course:Teacher>

<rdf:Description about="http://www.cs.umb.edu/~ram">

<Course:Name>Robert A. Morris</Course:Name>

<Course:Office>S/3/075</Course:Office>

</rdf:Description>

</Course:Teacher>

</rdf:Description>

RDF

<rdf:Description about="http://www.cs.umb.edu/Programs/grad_Course.html#CS639">

<Course:Teacher>

<rdf:Description about=http://www.cs.umb.edu/~ram

Course:Name="Robert A. Morris" Course:Office="S/3/075" />

</Course:Teacher>

</rdf:Description>

RDF

<rdf:RDFxmnls:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"xmnls:Course= "http://www.cs.umb.edu/schemas/Course"

<rdf:Description about="http://www.cs.umb.edu/Programs/grad_Course.html#CS639">

<Course:Teacher> <rdf:Description

about="http://www.cs.umb.edu/~ram"

Course:Name="Robert A. Morris" Course:Office="S/3/075" />

</Course:Teacher></rdf:Description>

</rdf:RDF>

Types

<rdf:RDFxmnls:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"xmnls:Course= "http://www.cs.umb.edu/schemas/Course"

<rdf:Description about="http://www.cs.umb.edu/Programs/grad_Course.html#CS639">

<Course:Teacher> <rdf:Description

about="http://www.cs.umb.edu/~ram" rdf:type=

"http://www.cs.umb.edu/schemas/Course/Person" Course:Name="Robert A. Morris" Course:Office="S/3/075" />

</Course:Teacher></rdf:Description>

</rdf:RDF>

Processing resource descriptions

• A central point about RDF is to be able to reason about and otherwise process descriptions.

• I.e., want to talk about the properties of descriptions, such as

– are they true?

– where are they asserted?

– If a certain statement is true, should some other thing also be true?

• Turning a Description into the kind of thing that can itself be described is called reification

Beyond RDF: The Semantic Web;interpreting information

• Thesaurus: synonyms

• Ontology: in philosophy, the study of things that can be described and their relationships. In CS: concepts and their relationships

• Knowledge base (facts base): sentences that are true or accepted as hypothesis