Chapter 4. Specialized RDF Relationships: Reification, Containers, and Collections

Reification, collections, and containers deserve separate coverage from the rest of the RDF/XML syntax, primarily because these constructs have caused the most controversy and confusion. And most of this has to do with meaning.

It isn't precisely clear what is happening, for instance, when I use reification syntax within an RDF/XML document. Am I making a statement about a statement? Am I claiming a special truth for the statement? Or how about the use of a collection or container—is there an interpretation of the relationship of the items within the groups that extends beyond the fact that the items are grouped?

During the process of revamping the RDF specification, the RDF Working Group at one time actually pushed for the removal of containers because the semantics associated with them could be easily emulated using rdf:type. There was also less than general approbation for the concept of reification, which no one seemed to be quite happy with. However, the group kept containers and reification, as well as adding in collections, but with a caveat: no additional semantics are attached to these constructs other than those that carefully delimited within the RDF documentation. Any additional interpretation would then be between the RDF toolmaker and the people who built the RDF vocabularies and used the tools. However, even within this, there is common acceptance of additional semantics, particularly as semantics relate to containers; of that, one can almost be guaranteed.

In this chapter, we'll not only look more closely at the physical aspects of reification, collections, and containers, we'll also look at what they "mean," intended or otherwise.