I don't think this should be built into the schema. These values should be controlled at the application level, perhaps using external controlled vocabularies (e.g., SKOS, OWL, etc...), and profiling mechanisms such as schematron.
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I don't think this should be built into the schema. These values should be controlled at the application level, perhaps using external controlled vocabularies (e.g., SKOS, OWL, etc...), and profiling mechanisms such as schematron.