I came across a mention of 'Digital Object Identifiers' in a paper on digital humanities, and discovered DOI.org:

A DOI name – a digital identifier for any object of intellectual property. A DOI name provides a means of persistently identifying a piece of intellectual property on a digital network and associating it with related current data in a structured extensible way.

A DOI name can apply to any form of intellectual property expressed in any digital environment. DOI names have been called "the bar code for intellectual property": like the physical bar code, they are enabling tools for use all through the supply chain to add value and save cost.

A DOI name differs from commonly used internet pointers to material such as the URL because it identifies an object as a first-class entity, not simply the place where the object is located. The DOI name identifies an entity directly, not some attribute of an object (an address is an attribute of a thing, whereas the thing itself is a first class object).

At some stage I have a big post to write about stable, permanent URIs for museum objects, and I'll be re-visiting this site when I start that.