[Auscope-geosciml] CGI Value abomination

Simon Cox simon.cox at jrc.ec.europa.eu
Tue Sep 1 03:10:04 EDT 2009

Ollie, others:
I have been grumbling about this for a while, and hope that it can be
addressed in the upcoming meeting in Quebec. 
Way too many of the class attributes in GeoSciML use CGI_Value and its
I am fully aware of the history of when CGI_Value it was created (Ottawa,
2005) and its value (it allowed us to move forward on the bigger issues). 
It also allowed a lazy UML design process, where for most atttributes the
type was set following a logic of just 'we can't really think about this now
but it'll be some kind of word/number'. 
Now I think it is time to set it aside and move on. 
My fundamental objections to the almost ubiquitous use of CGI_Value are
(i) it is hard to implement - it relies on XML Schema substitution groups
(ii) it is not compatible with any other domain schema
(iii) it allows data providers to be 'lazy' and create instances that are
not interoperable on arrival
(iv) it forces decisions required for data-fusion over to the client - this
is fundamentally what a standard encoding is supposed to avoid!
(v) it privileges a marginal GeoSciML use-case (transmission of field data)
at the expense of the dominant use-case (exchange of quality-controlled
archival data). 
Most of the time, the client will refer to 'standard definitions' provided
in the GeoSciML concept schemes to translate the values provided into
standard forms anyway, so why not get the provider to do that rather than
the client
It is the job of the GeoSciML design task group to actually make some
choices, fix the type of the basic class attributes, and then require that
service providers conform - make them make the choice about the 'best' value
for an attribute, don't shirk the job and push it back to the client. 
Almost all CGI_Value should be replaced by 
(a) ScopedName
(b) Measure
with just a few being 
(c) Range (new type)

Simon Cox

European Commission, Joint Research Centre 
Institute for Environment and Sustainability 
Spatial Data Infrastructures Unit, TP 262 
Via E. Fermi, 2749, I-21027 Ispra (VA), Italy 
Tel: +39 0332 78 3652 
Fax: +39 0332 78 6325 
 <mailto:simon.cox at jrc.ec.europa.eu> mailto:simon.cox at jrc.ec.europa.eu 

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