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ServiceType (svc)
The ServiceType says what the user wants done with the Referent — fetch the full text, request a loan, look up an abstract. Communities define the vocabulary.
The ServiceType entity names the kind of service the user is asking the resolver to perform. In KEV form the prefix is svc. The ServiceType is optional and may occur more than once in a single ContextObject — the user may, in principle, request several services simultaneously.
What the standard says
Z39.88-2004 establishes the ServiceType as part of the architecture but does not define a vocabulary of types. The catalogue of valid service types — full text, abstract, table of contents, citation export, ILL, holdings check — is left to communities of implementers. There is no registered list of standard ServiceType values.
How resolvers actually use it
In typical SAP1 traffic, the ServiceType is omitted. The user sends a ContextObject; the resolver presents a menu of available services (a "resolver menu") and lets the user pick. Where ServiceType is present, it is usually a hint emitted by a specific source system whose resolver understands the same vocabulary — for example, a citation manager asking for "export" or "full text" by convention.
Example
svc_id=info:ofi/svc:fulltext
&svc.format=htmlThe form of svc_id is conventional only. No registered value exists in the Registry.