[Digir-protocol] Substitutable Elements

[Hobern, D. <DH...@gb...>]

(I need to think about this area much more than I have so far done.  I may
well do this in England over the next few days.  I also understand that many
of you have been thinking about this for far longer.)

There are clearly other (possibly simpler) ways for us to define the
relationships between schema elements than by using substitutable elements.
I am certainly tempted by the idea of just defining the federation schema
and then adding attributes from a DiGIR namespace, where these attributes
define the essential characteristics of each element as it relates to DiGIR
(e.g. whether it is queriable, and if so, what class of query operations is
appropriate).  Possibly a compiler could then be used to derive a more
natural query schema from the federation schema.  Secondary configuration
documents could still be used to define the mapping to the physical data
model.

In any case I believe that (whether we stick with using substitutable
elements or something more like attributes), we need to model more
information within the protocol schema.  In particular, can we lose Darwin
Core bounding box in favour of identifying that Location is an element which
is an instance of a 'CoordinateSubstitutableElement'?  We could then simply
allow software to deduce that a bounding box query construct can be applied
when querying it.  This would allow the concept to become a generalised part
of the protocol rather than a special case for one particular coordinate
element.

Donald

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Donald Hobern
Programme Officer for Data Access and Database Interoperability
Global Biodiversity Information Facility Secretariat
Zoological Museum - University of Copenhagen
Universitetsparken 15, DK-2100 Copenhagen, Denmark
Tel: +45-35321483 Fax: +45-35321480 E-mail: dh...@gb...
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