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

Rick,

> One of the long-running issues with Part 6 has been the lack of an
> adequate set of use cases.

I also tried to enumerate design choices in my mail
"[dsdl-discuss] Re: FW: [office-comment] Ambiguity problems caused by a:defaultValue"

> 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

Is this really a good restriction? We might want
to assign an English key attribute as well as a Japanese
key attribute. Unlike DTDs, Part 6 should allow more than
one set of keys.

> * The data values of IDs must be document Unique

I agree with this restriction, although
scoped keys have been used by W3C XML Schema.

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

I am not sure if we need UNIQUE. The only point of UNIQUE is
to make keys optional. Do we need this optionality?

> 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

Some of your examples require foreign keys. I missed them in my
previous mail.

Now that OOXML heavily uses foreign keys, I think that
it is probably a good idea to cover foreign keys.

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

This makes sense. I think that this is possible by using
two sets of keys. The first set is for the first stage, while
the second one, the second stage.

> 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

Yes, foreign keys.
>
> 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)

This is intereseting and very web-oriented. But are these features
identity constraints?

> 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.

I have been thinking about the use of STX. I
am pessimistic now. In my understanding, STX does
not allow programmers to create a key set and check
if a referenced key already exists in the key set.

-- 
MURATA Makoto <murata@hokkaido.email.ne.jp>
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