Identifiers

When an Entity is known by a stable identifier (a DOI, a PubMed ID, an ISBN), the identifier can be sent in that Entity's _id key, for example rft_id. OpenURL 1.0 writes identifiers as URIs, usually in the info: scheme (RFC 4452) or as URNs.

Common identifier forms

There is no info:isbn namespace. Use urn:ISBN: or the rft.isbn metadata key. The OpenURL Registry lists info:doi, hdl, pmid, bibcode, oai, sici, oclcnum, lccn and sid; info:arxiv was registered (2006) in the general info-URI registry rather than in the OpenURL Registry, but is accepted by major resolvers.

Where identifiers go

Identifiers are placed in the <entity>_id key of the Entity they describe. For the Referent:

rft_id=info:doi/10.1103/PhysRev.47.777

For the Referrer, the conventional form is an info:sid URI:

rfr_id=info:sid/elsevier.com:ScienceDirect

An info:sid identifier has two parts: an Internet domain name (or host name) associated with the source, and an optional colon-separated string giving more detail, typically a database name. It is case-insensitive. This is a plain domain name, not reversed.

Several rft_id pairs may describe the same Referent; they are alternative identifiers for one item, not several items:

rft_id=info:doi/10.1126/science.275.5304.1320
&rft_id=info:pmid/9036860

Identifier and metadata together

Sending both an identifier and descriptive metadata is good practice: a resolver can use the identifier when its knowledge base knows it and fall back to metadata otherwise.

rft_id=info:doi/10.1103/PhysRev.47.777
&rft_val_fmt=info:ofi/fmt:kev:mtx:journal
&rft.atitle=Can+Quantum-Mechanical+Description+of+Physical+Reality+Be+Considered+Complete%3F
&rft.jtitle=Physical+Review
&rft.aulast=Einstein
&rft.date=1935
&rft.volume=47
&rft.spage=777

Identifier-only requests

A ContextObject may describe the Referent by identifier alone. The minimal useful OpenURL is therefore:

https://resolver.example.edu/openurl?
url_ver=Z39.88-2004
&ctx_ver=Z39.88-2004
&rft_id=info:doi/10.1103/PhysRev.47.777

Strictly, rft_val_fmt is only required when rft.* keys are present. Many sources include it anyway, and some resolvers use it as a hint about the item type.

Sources

• ANSI/NISO Z39.88-2004 (R2010), The OpenURL Framework for Context-Sensitive Services.
• OCLC Research, frozen (deprecated) copy of the OpenURL Framework Registry.
• info:sid namespace registration (frozen info-URI registry).
• Crossref OpenURL documentation.