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From "Martin Desruisseaux (JIRA)" <j...@apache.org>
Subject [jira] [Created] (SIS-82) Metadata implementations could use a single field for union
Date Thu, 21 Mar 2013 14:23:16 GMT
Martin Desruisseaux created SIS-82:
--------------------------------------

             Summary: Metadata implementations could use a single field for union
                 Key: SIS-82
                 URL: https://issues.apache.org/jira/browse/SIS-82
             Project: Spatial Information Systems
          Issue Type: Improvement
          Components: Metadata
            Reporter: Martin Desruisseaux
             Fix For: 0.3


The ISO 19115 specification defines some properties as conditional. Most of the time, they
are a set of mutually exclusive properties. For example the {{MD_Resolution}} class defines
two properties: {{equivalentScale}} and {{distance}}, both of them flagged as conditional.
The specification said: "_Only one of equivalent scale and ground sample distance may be provided_".

Currently those two properties are defined in separated fields and could be defined together.
We could replace the two private fields by a single private {{Object}} field, and use {{instanceof}}
check in getter methods. The advantage would be:

* Automatically gain enforcement of the ISO specification.
* Save a little bit of memory space for metadata instances.

One consequence is that if an XML document contains two properties, the last property would
silently overwrite the previous one at unmarshalling time. To prevent such thing to happen
silently, we would need the {{APPENDABLE}} mode proposed in SIS-81.


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