Transports

A transport is the mechanism that moves a ContextObject from the system that created it to a resolver. Z39.88-2004 defines three OpenURL transports, each registered for HTTP and HTTPS and each usable with GET or POST. All three share the transport keys that begin url_.

Inline

The KEV pairs of exactly one KEV ContextObject are placed directly in the query string, next to the transport keys. This is what nearly every OpenURL in the wild looks like, and the standard notes that it "strongly resembles OpenURL 0.1". Inline can only carry a KEV ContextObject.

https://resolver.example.edu/openurl?
url_ver=Z39.88-2004
&url_ctx_fmt=info:ofi/fmt:kev:mtx:ctx
&ctx_ver=Z39.88-2004
&rft_val_fmt=info:ofi/fmt:kev:mtx:journal
&rft.atitle=An+Article+Title
&rft.jtitle=A+Journal
&rft.date=2020
&rfr_id=info:sid/example.com:database

url_ver

Required. Fixed value Z39.88-2004.

url_tim

Optional. Creation time of the OpenURL.

url_ctx_fmt

Optional for Inline. If present, info:ofi/fmt:kev:mtx:ctx.

Any other key that is neither a url_ key nor a KEV ContextObject key is a foreign key: allowed, but with no meaning defined by the standard. Resolvers may ignore it. Old 0.1 keys such as sid or genre in a hybrid OpenURL are foreign keys from a 1.0 point of view.

By-Value

The complete ContextObject representation becomes the value of a single key, url_ctx_val, and url_ctx_fmt says which ContextObject Format it uses. Because a KEV ContextObject is already URL-encoded and is then encoded again as a value, its contents end up double-encoded (%3A becomes %253A). The same ContextObject as above, By-Value over GET:

https://resolver.example.edu/openurl?url_ver=Z39.88-2004
&url_ctx_fmt=info%3Aofi%2Ffmt%3Akev%3Amtx%3Actx
&url_ctx_val=ctx_ver%3DZ39.88-2004%26rft_val_fmt%3Dinfo%253Aofi%252Ffmt%253Akev%253Amtx%253Ajournal%26rft_id%3Dinfo%253Adoi%252F10.1103%252FPhysRev.47.777%26rft.jtitle%3DPhysical%2BReview%26rft.date%3D1935

url_ver

Required.

url_ctx_fmt

Required. info:ofi/fmt:kev:mtx:ctx or info:ofi/fmt:xml:xsd:ctx.

url_ctx_val

Required. The ContextObject representation itself.

By-Value can carry an XML ContextObject too, which is why SAP2 uses it. It is rare in ordinary linking.

By-Reference

The ContextObject representation is stored at a network location and the OpenURL carries only that location. The resolver fetches it before processing. This suits large XML ContextObjects or bundles of several ContextObjects.

https://resolver.example.edu/openurl?
url_ver=Z39.88-2004
&url_ctx_fmt=info:ofi/fmt:xml:xsd:ctx
&url_ctx_ref=https://source.example.com/contextobjects/12345.xml

url_ver

Required.

url_ctx_fmt

Required.

url_ctx_ref

Required. The URL of the ContextObject representation.

GET or POST

With GET, the KEV pairs form the query string after the resolver's base URL. With POST, the same string is sent as the message body with Content-Type: application/x-www-form-urlencoded. POST avoids URL-length limits; GET is what a clickable link uses.

URL length

Appendix E of the standard sets no maximum length, but says resolvers must accept OpenURLs of at least 255 bytes after encoding and should accept at least 2048 bytes. Long author lists or abstracts can exceed what some proxies and browsers handle; POST or By-Reference avoid the problem.

Where COinS fits

COinS is not a transport defined by Z39.88-2004. It is a community convention for embedding a KEV ContextObject in an HTML <span>. Client-side software later turns it into an Inline OpenURL to the user's resolver.

Choosing a transport

• Use Inline over GET for links from databases, catalogues and reference lists. Include url_ver=Z39.88-2004 and ctx_ver=Z39.88-2004.
• Use Inline over POST or By-Reference when the ContextObject is too large for a URL.
• Use By-Value or By-Reference when sending XML ContextObjects.

Sources

• ANSI/NISO Z39.88-2004 (R2010), The OpenURL Framework for Context-Sensitive Services.
• NISO Committee AX, The KEV Format Implementation Guidelines (v1.7, 2004-12-09).
• OCLC Research, frozen (deprecated) copy of the OpenURL Framework Registry.