[dsdl-discuss] Use cases for DSDL Part 6 Path based integrity constraints (discussion draft)

One of the long-running issues with Part 6 has been the lack of an
adequate set of use cases. I suggest that we need to look at the larger
issue of link-base integrity, and to assist the new generation of
XML-in-ZIP formats. Comments and improvements are welcome. In
particular, I think Part 6 needs to be where we provide facilities to
break out of the single document model (old-timers: I am not suggesting
we need HyTime Bounded Information Sets unless there is a use case.)
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DSDL Part 6 - Path-based integrity constraints should be developed to
meet the following requirements:

1) It should allow declaration and checking of all the constraints of
SGML, XML 1.0 and XML 1.1 IDs:
   * The lexical form of the ID (in particular, matching different
naming rules)
   * There can only be one ID attribute per element
   * The data values of IDs must be document Unique
   * Metadata labelling of the attribute as an ID

2) It should allow declaration and checking of all the constraints of
SGML, XML 1.0 and XML 1.0 IDREF and IDREFS

3) It should allow declaration and checking of all the constraints of
SGML CONREF and SVG value inheritance
  * In particular, this relates to providing declarations that the
value of an implied attribute shall come from some attribute either
higher or lower in the instance from the current element node.

4) It should allow declaration and checking of all constraints of XML
Schemas KEY, UNIQUE and KEYREF mechanisms.

5) It should allow declaration and checking of simple links, in
particular HTML a/href, image/src, head/meta, ODF package-internal
links, and XML pi()[name()='xml-stylesheet']
  * This should cope with URLs which contain fragment references

6) It should allow checking of two stage links, in particular SGML and
XML SYSTEM identifiers through OASIS XML Catalogs, OOXML OPC links

7) It should allow checking of external links and external markup, in
particular complex XPath link bases.
  * There is no necessity to provide a declaration mechanism: the XPath
declarations are adequate

7) It should allow validation of reached documents or media files
accessed through links.
  * The reachability of the resource
  * That the resource is the format expected by anchor-side metadata
  * That the resource is the format labelled using the target-side
metadata (e.g. in a MIME header)
  * That metadata associated with the resource is correct (e.g. for
read-write)

8) There is no requirement or expectation that this should be
implementable using XSLT 1 or 2. However, streamable implementation in
one or two passes should be favoured.

Cheers
Rick Jelliffe

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