adl:types

The adl:types bucket contains terms that precisely specify an object's form or content. In general, a type is the target of an "is-a" relationship; that is, a type can be applied to an object if the assertion "object is a type" makes sense. Valid terms for the type bucket are drawn from an ADL-controlled hierarchical vocabulary. The single query operation defined on the type bucket is thus an exact match against nodes or leaves in the type hierarchy.

The adl:types and adl:format buckets are the only buckets for which we currently mandate specific sets of valid terms. This is a difficult decision, for it means that we (or somebody) must serve as the controlling authority for these term lists. In the particular cases of the adl:types and adl:format buckets, the need for program-level interoperability is strong enough, and the scope of the term spaces constrained enough, to make controlled vocabularies both useful and feasible. In the specific case of the adl:types bucket, for example, we are growing the type schemes for catalogs and gazetteers by merging existing domain-specific vocabularies.