Instance Header improvements in CMDI 1.2: Executive summary
This page provides an executive summary of the issue and proposed solution fully described in CMDI 1.2/Header.
Issue description
- In CMDI 1.1, all header elements are optional including
<MdProfile>. Because of this, and the fact that the@xsi:schemaLocationattribute cannot be made mandatory either, it is possible to create schema valid CMDI instances that do not link back to the profile they are based on.
- Because the granularity of the existing CMDI files and collections varies a lot (from 1 CMDI = 1 large corpus to 1 CMDI file = single small textfile) it would be handy to indicate that certain CMDI descriptions are about a collection as a whole.
Description of proposed solution
The solution to the first issue is to make the <MdProfile> element a mandatory element. All CMDI instances must therefore contain this element and thus, it is possible to always definitely determine their profile. It was decided against allowing a unknown value for the <MdProfile> element, because it would essentially make this element optional again. The automatic up-conversion to CMDI 1.2 is therefore not possible for CMDI 1.1 instances, that lack a proper <MdProfile> element and @xsi:schemaLocation attribute and users need to intervene manually.
For the second issue, several solution where proposed and discussed, including but not limited to adding a type indicator to the header or promoting a collection component or profile. However, all these solutions have more disadvantaged then advantages. It was decided, to adopt a solution to this problem "outside of CMDI". As a best practice suggestion, centers shall be encouraged to use certain data categories in their root profiles to distinguish between collection level and terminal level CMDI instances. The rationale behind this decision is that the classification of the complexity of resources leads to another metadata value in its own right, whereas the scope of CMDI should be kept restricted to describing the structure of the metadata and the interface to the metadata semantic.
