The fourth component of PROV-DM is concerned with relations specialization and alternate between entities. Figure figure-component4 overviews the component.
Wherever two people describe the provenance of a same thing, one cannot expect them to coordinate and agree on the identifiers to use to denote that thing.
User Alice writes an article. In its provenance, she wishes to refer to the precise version of the article with a date-specific URI, as she might edit the article later. Alternatively, user Bob refers to the article in general, indepedently of its variants over time.
To allow for identifiers to be chosen freely and independently by each user, the PROV data model introduces relations that allow entities to be linked together. The following two relations are introduced for expressing specialized or alternate entities.
The BBC news home page on 2012-03-23 ex:bbcNews2012-03-23 is a specialization of the BBC news page in general bbc:news/. This can be expressed as follows.
specializationOf(ex:bbcNews2012-03-23, bbc:news/)Given that the BBC news does not define a URI for today's news page, we are creating a qualified name in the namespace ex.
entity(bbc:news/science-environment-17526723, [ prov:type="a news item"]) entity(bbc:news/mobile/science-environment-17526723, [ prov:type="a news item"]) alternateOf(bbc:news/science-environment-17526723, bbc:news/mobile/science-environment-17526723)
They are both specialization of an (unspecified) entity.
entity(tr:WD-prov-dm-20111018) entity(tr:WD-prov-dm-20111215) alternateOf(tr:WD-prov-dm-20111018,tr:WD-prov-dm-20111215)
They are both specialization of the page http://www.w3.org/TR/prov-dm/.