In Java, such collections of definitions can be grouped into Packages. In XML, they can be grouped into Namespaces. So, a pragmatic way to factor out this metadata (such that it is not copied into every "fact"), is to give the ontology a name and tag each fact with that name (in the same way as each Java value is "tagged" with a data type that includes the Package name/path). And since, XML has already defined URIs as the format for namespace identifiers, and it is easy to map Package names with URIs, Existential Programming systems/languages could use URIs to identify the ontology associated with some set of facts. Since Existential Programming systems seek to seamlessly convert between an O/O and an E/R and an S/N representation, having OO packages easily mappable to data exchange mechanisms like XML is a good thing.
|POSTSCRIPT - Nov 23rd, 2007|
|It is hard to tell which of my epiphanies are new and which are things I read long ago but later remembered as if they were a new idea...I'm sure I read this URI stuff in the Semantic Web articles (see Principle #1), but only "remembered" it when stumbling back across it today. At any rate, it was only recently that Tim Berners-Lee wrote this post about Linked Data using URIs.|