Spec: 4.3.9 ALIASES: HS_ALIAS

It is possible that the set of elements (i.e., type-value pairs) of a digital object may be included in other digital objects and thus multiple identifiers could be associated with the same information represented in digital form, thus creating, in effect, multiple different digital objects all with the same information represented in digital form. DO-IRP does not specify a specific mechanism for identifier records to reference all such alternatives, but various DO-IRP implementations and their users should use the pre-defined HS_ALIAS type in such cases.

An HS_ALIAS element is one whose field is HS_ALIAS and whose field contains a reference to another identifier. An identifier whose record contains an HS_ALIAS element is an alias to the identifier referenced in the HS_ALIAS element. An alias record should not have any additional elements other than HS_ALIAS or HS_ADMIN (for administration) elements. This is necessary to prevent any inconsistency between an identifier and its aliases.

During an identifier resolution, a client may get back an HS_ALIAS element. This indicates that the identifier in question is an alias identifier. The client may then retry the query against the identifier specified in the HS_ALIAS element until final results are obtained.

The use of HS_ALIAS introduces a number of special considerations. For example, multiple levels of aliases should be avoided for the sake of efficiency, but are not signaled as an error. Alias loops and aliases that point to non-existent identifiers should be caught and error conditions passed back to the user.