CIMI has also been trying to develop a future-proof framework for linking to people, objects, etc. The idea is that each concept of interest (say the artist Rembrandt) is assigned a unique, unchanging "handle". This can then act as a link to "whatever we have on Rembrandt". So far, within Project CHIO, external entities are expressed as [SGML] Formal Public Identifiers (FPIs). This approach removes system-dependent information (e.g., a URL) from the documents themselves and puts it into the associated catalog file. This simplifies the maintenance of links. However, it is clearly not feasible to have a catalog file containing a separate FPI for every object, person, place, etc. in the world!
Recent work suggests that future-proof links can be achieved by having FPIs for authorities such as the Art and Architecture Thesaurus, and then expressing the handle as a two-stage location ladder. This means that handles will take the general form " find this object/concept/person/place within this authority" (e.g., "find the concept Rembrandt within the Unified List of Artists' Names"). Now we only require an FPI for each authority used by musems: an entirely practical proposition.
HyTime and TEI extended pointers both offer a wealth of mechanisms for pointing to the correct place, but clearly the SGML ID-IDREF mechanism is the most robust option, and guarantees uniqueness. This is another reason for expressing authorities in SGML format (see the next section).
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Contact Robin Cover with corrections and updates, or to submit contributions to the ISUG online document database.
