[Ex-plain] Explain and ZING

Alan Kent ajk at mds.rmit.edu.au
Tue Mar 12 08:39:11 CET 2002

On Wed, Mar 06, 2002 at 11:17:35PM +0000, Robert Sanderson wrote:
> > Please give this some though, as I think there is
> > alot to be gained by aligning the two, even though
> > there are different requirements, and aligning the
> > two would present some complexity, as, for
> > example, SRW doesn't use the database concept.
> Can I request then that someone who is familiar with the ins and outs of 
> SRW and what would be required to describe it go through and make a list 
> of what would need to be changed in the current format so that it can be 
> discussed whether or not this would add too much complexity overhead?
> The idea is to get a neat and lean set of XML elements so that it's easy
> to implement against current servers,  encorporating the necessary
> information from Explain and the Friends and Neighbours proposal.  
> Hopefully SRW will fit within the elements already defined, I'm not up to
> date on it enough to comment either way however.
> Rob

I am not at all convinced that Explain-- and SRW explain can be
the same. Explain-- to me describes a database in a Z39.50 target.
It describes attribute lists etc. A SRW implementation might use
Explain-- to find out about a database (that is certainly what
I intend to do). However, SRW-explain information should describe
a database from an SRW perspective. The XML might want to be designed
to drop into a WSDL file (and so kept very minimal). Attribute lists
seem completely out of scope here. SRW just wants names of access
points to use in queries (and function/overlay names if I convince
others :-). SRW does not want to describe attribute lists in my
opinion. Its trying to hide them.

So I think Explain-- is very interesting and very useful. But I don't
think its suitable for direct use by SRW. I think it will be a
subset (remove attribute lists, remove repeating elements where
possible, etc). Explain---- for want of a better name...

With SRW, it is not even definite if explain records are going to
be a record syntax or directly encoded in a WSDL file. If a record
syntax, Explain-- may be attractive in its current form. If its going
to be embedded in a WSDL file, then the structure of the XML is
much more important as its going to be turned into 'struct'
definitions etc in a programming language. Avoiding nested structs
and repeating groups becomes much more important.


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