Wednesday, December 20, 2006

Some Design Issues

Semantic Web Road map "It is clearly important that the query language be defined in terms of RDF logic. For example, to query a server for the author of a resource, one would ask for an assertion of the form "x is the author of p1" for some x. To ask for a definitive list of all authors, one would ask for a set of authors such that any author was in the set and everyone in the set was an author. And so on."

Relational Databases on the Semantic Web "Is the RDF model an entity-relationship mode? Yes and no. It is great as a basis for ER-modelling, but because RDF is used for other things as well, RDF is more general. RDF is a model of entities (nodes) and relationships. If you are used to the "ER" modelling system for data, then the RDF model is basically an openning of the ER model to work on the Web. In typical ER model involved entity types, and for each entity type there are a set of relationships (slots in the typical ER diagram). The RDF model is the same, except that relationships are first class objects: they are identified by a URI, and so anyone can make one. Furthurmore, the set of slots of an object is not defined when the class of an object is defined."

Linked Data "The Semantic Web isn't just about putting data on the web. It is about making links, so that a person or machine can explore the web of data. With linked data, when you have some of it, you can find other, related, data."

"So statements which relate things in the two documents must be repeated in each. This clearly is against the first rule of data storage: don't store the same data in two different places: you will have problems keeping it consistent. This is indeed an issue with browsable data. A set of of completely browsable data with links in both directions has to be completely consistent, and that takes coordination, especially if different authors or different programs are involved."
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