Re: Element sets, schemas, and record syntaxes

> Date: Wed, 18 Feb 2004 13:29:35 +1100
> From: Alan Kent <ajk@mds.rmit.edu.au>
> 
> Q1: Theoretically, should the places where a schema OID is present
> in Explain (for example, the non-key 'schema' field of
> ElementSetDetails) really now be OID or URI (a CHOICE)?

I suppose so.

> I often read the Explain ASN.1 as a way of understanding the Z39.50
> data model, as it defines in effect an E-R diagram of the Z39.50
> concepts (including what should be keys).

Sheesh, Alan, no-one takes that stuff _seriously_!  1/2 :-)

> Q2: Can you specify the "XML" record syntax, the same element set
> name, but request a different schema to get back different XML
> content?  Or does the element set name and record syntax (eg: "XML")
> uniquely identify the schema to use?

For XML records, there is no distinction between schema and
element-set; or, to say the same thing a different way, the concept of
element-set is subsumed into the broader concept of schema.  You would
not ask for XML records in the Foo schema using "F" and "B" element
sets; instead, you would ask for XML records in Foo-F and Foo-B
schemas.  For the sake of simplicity, this information (the string
indicating the schema name) is carried in the element-set name field,
in according with an implementor agreement (or something) made last
year.

> I wonder if it is now more accurate to say the schema is now part of
> the key. If not, there does not seem much point in being able to
> request a particular schema.

Well, the element-set is part of the schema, and the schema is what's
in the element-set name field, so ...  Yes.  I suppose.

> If the schema is now part of the key of ElementSetDetails in
> Explain, its backwards compatible (all old implementations are still
> correct), but the 'schema' of ElementSetDetails should now be a part
> of the key (and possibly now be allowed to be a URI, not just an
> OID).

... though of course Explain Classic is at best moribund these days.

 _/|_	 _______________________________________________________________
/o ) \/  Mike Taylor  <mike@indexdata.com>  http://www.miketaylor.org.uk
)_v__/\  "Furious activity is no substitute for understanding" --
	 H. H. Williams.

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Received on Thursday, 19 February 2004 10:51:36 UTC