Extending XCRI-CAP
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[edit] Overview
There are a number of extension mechanisms that you can use in XCRI-CAP:
- Adding a property from another namespace
- Constraining the structure of a property using a syntax encoding scheme
- Constraining the values of a property using a vocabulary encoding scheme
Information on the different methods is given below.
If you make an extension, please add it to the XCRI-CAP Extensions Registry.
[edit] Inclusion of additional properties
XCRI-CAP already makes use of some external schemas, such as XHTML. Implementers are free to include additional elements where the XCRI-CAP schema permits, provided this is done (1) using an explicitly referenced namespace, and (2) the resource or property permits extension in the XCRI-CAP XSD. There are no particular limits on the type or structure of additional properties.
[edit] Encoding schemes
XCRI-CAP makes extensive use of encoding schemes to handle a range of diverse value-spaces, both for structured values (syntax encoding schemes) and controlled vocabularies (vocabulary encoding schemes). For example, properties such as identifier are designed to be used in conjunction with encoding schemes to enable the representation of third-party identification mechanisms, so that a course can be identified using the identifier issued by the institution, the identifier expected by a major broker such as UCAS, and with the identifier issued by other agencies. Aggregators and brokers should check the values of elements for encoding schemes so that they make use of the correct value for their business rules.
[edit] Syntax encoding schemes
The general pattern of usage for syntax encoding schemes follows that of Dublin Core, with the use of the xsi:type attribute to identify the encoding scheme used for the enclosed value by a URI consisting of a namespace prefix and the encoding scheme name. For example:
<identifier xsi:type="ukrlp:ukprn">12345</identifier>
The following encoding schemes are known for use with XCRI-CAP within the context of the identifier element:
- ukrlp:ukprn The UK Unique Provider Reference Number
- ???:??? UCAS course ID
The following encoding schemes are known for use with XCRI-CAP within the context of use of dc:subject for courses:
- ???:??? UCAS JACS code --scottwilson 23:25, 20 March 2007 (UTC)
- Lots of subject codes as used in DC? --scottwilson 23:25, 20 March 2007 (UTC)
[edit] Vocabulary encoding schemes
The following vocabulary encoding schemes are defined within XCRI-CAP for use with the description element:
These are used differently from the syntax encoding schemes above. Check the documentation of the description element for usage.
Implementers are of course free to add other vocabularies. To use these it is suggested that the xsi:type attribute is used to qualify the element that the vocabulary is being applied to as being of a qualified type. The type itself should be defined in a referenced schema using an XML Schema enumeration.
