Introduction to Persistent Uniform Resource Locators

Introduction to Persistent Uniform Resource Locators: "What resources should have PURLs?

Users should assign a PURL to any discrete resource for which reliable access over time is desired. For example, a home page, an electronic journal, an individual article, or a paper are good candidates for a persistent name. Some dynamic resources such as 'today's newspaper' or 'closing price of Foo stock' are also good candidates.

Nondiscrete resources such as sections within a document or charts or graphics that would not make sense outside the context of their containing document are not good candidates for PURLs. Temporary resources are also poor candidates.

Objects at the top of hierarchies of objects that might be moved as a unit are excellent partial redirect candidates. Depending on the underlying nature of the hierarchy, the lower-level objects may not require PURLs. For example, if the hypertext object hierarchy corresponds closely to the hierarchy of the objects in the underlying file system and the hypertext links are relative links based on the file system hierarchy, then a single PURL for the top-level object in the hierarchy is all that may be necessary.

To create a PURL, point a Web browser to a PURL Resolver and follow the resolver's instructions for creating a PURL. PURL Resolvers provide a form to fill out to create a PURL. This form should provide a default public domain with universal write access.
Maintaining PURLs

PURLs are not updated automatically when their associated URL changes unless some outside process is run to notify the corresponding PURL Resolver. A maintainer must update the information in the appropriate PURL Server when the associated URL changes. It is the responsibility of a PURL's owner and its maintainers to update the PURL when the associated URL changes.

PURL maintenance can be performed by connecting to a PURL Resolver using a Web browser and then using the PURL Resolver's maintenance forms to make the appropriate changes to the desired PURL. Only authorized PURL maintainers can modify a PURL.

A PURL maintainer can turn off PURL resolution. This is done by entering a new, empty, URL on the PURL maintenance form for the PURL in question. This will cause a history page to be returned when resolution of the PURL is attempted. A history page for a PURL contains administrative information accumulated over time and details about past associated URLs.

PURL maintenance is an important difference between PURLs and several URN proposals. In some URN proposals, a URN is a permanent name for a unique resource and only that resource forever. Some URN proposals would allow the same resource to move, but would not allow a different resource to be associated with the URN. PURLs make the name permanent, but allow the associated URL to change.
Using PURLs"