xml-dev - XSD: Proposed Goals, Rev. 2

["Simon St.Laurent" <SimonStL@classic.msn.com>]

A revised set of goals for XSD follows, based on public and private comments.  
These are still open to change until Friday.  If there are changes today, I'll 
post them tomorrow, and again Friday morning.  Friday's version will hopefully 
be the final version.  We need to hammer this down and move on to more 
specific issues - syntax, implementations, and the rest of the fun.

Per previous usage, XSD (Extensible or XML Structure Definitions) refers to 
the standard under construction. SDD (Structure Definition Document) refers to 
the schema/XMLDTD/etc. created using that standard.  (Better definitions are 
on the list of things to come very shortly.)

1. SDDs shall use XML document syntax, using element nesting and attributes to 
describe all constraints that may be verified by a processor using XSD.

2. XSD shall define a transformation from SDDs to DTDs.

3. SDDs shall be capable of representing the normalized element and attribute 
structures defined in XML 1.0 DTDs.

4. SDDs shall be parseable, manageable, and manipulable using the same tools 
used to parse, manage, and manipulate XML documents.

5. SDDs shall be easy to create, read, and modify.

6. SDDs shall be easy to use in combination with a parser to provide 
structural validation of documents.

7. XSD shall include an SDD and an XML 1.0 DTD defining the structure of SDDs.

8. XSD shall suggest mechanisms for applying SDDs to documents.

9. XSD shall include mechanisms for extending the information included in 
SDDs.

10. The XSD specification shall be readable,clear, and rigorous, using 
terminology and nomenclature as close to the XML 1.0 specification as 
possible.

11. The XSD specification will comply with and be consistent with W3C 
recommendations regarding XML.

12. SDDs shall provide constructs for human- and machine-readable 
documentation.

---------------------------------
Note that sequence doesn't matter; I'm putting new entries at the end to avoid 
numbering confusion, not to indicate precedence.  

Additions: Documentation moved from number 5 to number 12.  Machine-readable 
documentation may be used by editors or to provide support for literate 
programming.  This is definitely not a place for style or similar processing 
information.

Modifications:

1 - Added "using element nesting and attributes to describe all constraints 
that may be verified by a processor using XSD."  This comes from Paul Prescod. 
 I didn't add the XLinks yet; I'd like to leave that open for discussion at 
this point.  It's an excellent idea, but I'd like to be a little further 
before locking ourselves into it.

2 - Replaced the previously loose language with Paul's stricter statement.

5 - Removed 'document' (went to 12) and added 'read'.

7 - Added 'an SDD' to the mix.  If we can't define our own structure with an 
SDD, it's probably not very useful.

10 - Added rigorous.

Questions:

3 - Paul Prescod suggested removing it.  I like it because it sets a limited 
task, the 'normalized' DTDs. I think 'capable of' leaves open the possibility 
that SDDs can do more than just this.

5 - Two private respondents have complained that 'easy' is too vague (as in 
'easy to create, read, and modify').  To me this means SDD's should be 
editable by a human with a reasonable knowledge of XML structures, but I can 
see where this may bother people.  I like the vagueness, I suppose.  Anyone 
have a clearer idea?

9 - Should we add some kind of bounds to keep SDDs from redefining document 
instance syntax?

12 - Alain Deseine proposed a metadata mechanism.  I hope we have the kinds of 
metadata he needs in this note.  I don't want to march on metadata a la RDF 
with this module. 

Simon St.Laurent
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