The 'tdb' and 'duri' URI schemes, based on dated URIs

This document defines two URI schemes. The first, 'duri' (standing for "dated URI"), allows indicating a URI as of a particular date (and time). This allows explicit reference to the "time of retrieval", similar to the way in which bibliographic references containing URIs are used. The second scheme, 'tdb' ( standing for "Thing Described By"), provides a way of using a way of minting URIs for anything that can be described, with the ability to fix the description to a given date or time. The 'tdb' URI scheme may reduce the need to define define new URN namespaces merely for the purpose of creating stable identifiers for concepts or abstractions: it provides a ready means for identifying "non-information resources" by semantic indirection — a way of creating a URI for anything.