adl:identifiers
The adl:identifiers bucket may contain any labels for the object that are defined with respect to an externally controlled vocabulary or production rule (such as ISBNs, technical report numbers, satellite image identifiers, etc.).These kinds of labels are useful for finding "known objects" for which the user knows the particular identifier. Digital data are often assigned identifiers as a function of their creation; published items often have ISBNs or ISSNs; "gray literature" often has unique technical report numbers.In effect, the adl:identifiers bucket provides a "trap door" into alternative cataloging schemes. A nomenclature that is well-defined elsewhere can be accessed through the adl:identifiers bucket, and often provides the simplest and most precise means of locating an object, assuming one is familiar with the nomenclature. (Of course, there is always a risk of false hits from multiple nomenclatures that use similar encoding rules; for example, an arbitrary10-digit numeric identifier could be mistaken for an ISBN code).
We assume that identifiers are normalized upon entry into the buckets (such as removing dashes from ISBNs), and that the search terms are likewise normalized prior to issuing a query. The adl:identifiers bucket has no knowledge of the structure or semantics of specific identifier types.