UCD for SIAP

[Sebastien Derriere]

Doug Tody wrote:
> 
> The key problem I see with trying to use existing UCDs is that historically
> UCDs have been used primarily as fuzzy tags to link similar fields in
> catalogs.  In data access metadata such as is introduced in SIA we are
> using UCDs to identify the fields of a formal data model.  Here the tag
> is not fuzzy at all, linking similar fields of unrelated catalogs, rather
> it is a link to a field of a formally defined data model.  Precision is
> important for these data models - we are precisely defining attributes
> of the data model.
> 
> We should formally define data models such as spectralBandpass or WCS
> and define, as part of the data model, the UCD tag used to identify an
> attribute of the data model.  When we represent a data model as a set of
> related columns in a table, or as an entity struct in XML (as in IDHA or
> HDX), we will use the UCDs to formally type the data model attributes so
> that programs can use them unambiguously, so that we can use XML Schemas
> for automated validation, and so forth.

  Hello,

  The primary goal of UCDs is to ensure interoperability between
heterogeneous datasets. That's why they have been defined to some
"reasonable" level of precision (what you call fuzziness).
  Internal attributes of a formally defined data model can be defined
at any level of precision, and have their own names. But you can
have *in addition* a UCD attached to every attribute (see the case 
of the IDHA model). Those UCD can ensure interoperability between
different data models, and between data models and datasets. 
  The names of the attributes can not a priori ensure this task,
because nothing prevents from having the same concept named 
differently in different models.

Sebastien.
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