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Using HTTP to Query

The most common method of submitting queries to CrossRef is to have an automated service interact with the CrossRef system using the HTTP interface. CrossRef strongly recommends that you group between 5 and 20 queries into a single request. This helps reduce the network transaction load on CrossRef resources. These transactions use a simple HTTP GET request with the results being returned immediately to the caller. Queries may also be processed off line in batch mode.

Synchronous HTTP queries

Synchronous queries are performed using a URL with encoded parameters as follows:

http://doi.crossref.org/servlet/query?usr=<USERNAME>&pwd=<PASSWORD>&format=unixref&qdata=|Proc.%20Natl%20Acad.%20Sci.%20USA|Zhou|94|24|13215|1997|||

http://doi.crossref.org/servlet/query?pid=<USERNAME>:<PASSWORD>&id=10.1577/H02-043

http://doi.crossref.org/servlet/query?pid=<EMAIL>&id=10.1577/H02-043

where:

• usr is your CrossRef-supplied login name.
• pwd is your CrossRef password.
• pid is your CrossRef-supplied login name and password or CrossRef Query Services email address.
• format is the desired results format (piped | xsd_xml | unixref)

HTTP queries may be submitted in piped format or as XML (recommended). XML queries can be submitted by HTTP by appending query XML to a HTTP request.Show Example

To place multiple queries in one request, include them in the qdata parameter separated by %0A, as shown here:

http://doi.crossref.org/servlet/query?usr=<USERNAME>&pwd=<PASSWORD>&qdata=|%20Natl%20Acad.%20Sci.%20USA|Zhou|94|24|13215|1997|||%0A|J.%20Mol.%20Biol.|Hagerman|260|||1996|||

Encoding

Certain characters cannot be passed in a URL without causing problems. The following table lists those characters that must be URL-encoded.
 

Notes:  

• For more information on URL encoding, see URL Encoding (or "What are those %20 codes in URLs?).
• DOI-to-metadata queries retrieve primarily item metadata. See "Retrieving DOI info-metadata" to retrieve information about a DOI such as timestamp prime/alias status.

HTTP Query Performance

There are several drawbacks to submitting synchronous HTTP queries:

• A network connection is established every time an HTTP request is made. Even with HTTP keep-alive the web server disconnects the client after a short period of inactivity. The establishment of a connection with every query request can be expensive, especially for one-line queries.
• User authentication on the CrossRef side occurs with every HTTP request. Because most clients do not maintain a session with CrossRef, the cost in terms of CrossRef resources of establishing a session to enforce user access rights for every request is substantial.
• Users can overcome the first two drawbacks by submitting multiple queries within the same HTTP request where queries are separated by CRLF. However, this technique presents a different problem: queries are evaluated sequentially within the same thread, which means "hard-to-resolve" queries slow down other queries within the same batch. So even though users gain in terms of network connection and CrossRef authentication time, they lose the concurrence provided by submitting one-line queries.

link

support@crossref.org

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