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First published 2003-08-28, last update: 2003-10-29.
TDWG working group: Structure of Descriptive Data (SDD)
Note: This document covers an open discussion point and currently only discusses the implications of computed characters on coding status!
In the discussions in Brazil 2002 and Paris 2003 we repeatedly discussed whether to support computed information. In a computed character, data in the object description would be generated automatically on the basis of terminological relationships and existing descriptive data. However, support for computed characters would add considerable complexity and burden on applications consuming SDD documents. It would be desirable that the result of a expressions are included in the SDD files for processors that do not support a reevaluation of the computed character expressions.
To support this, the computed character would consist of: a) an expression defining how to compute the result, b) the result in a form that would be recognized as cached, non-editable data, updatable only through evaluating the expression. The following additional coding status values would then be required:
In a further step, it may be profitable to separately define (c) the data items on which the expression depends. If this information is present, an editing SDD processor that is not able to compute the expression, but changes data on which the expression depends, could invalidate the expression and set the cached result to "CouldNotCompute".
Please send your criticism or suggestions to the SDD mailing list or to the author.
Gregor Hagedorn; Vers. 1; 29. October 2003