Here is a summarized list of five characteristics for great data element definitions:

Precise - The definition should use words that have a precise meaning. Try to avoid words that have multiple meanings or multiple word senses. Concise - The definition should use the shortest description possible that is still clear. Non Circular - The definition should not use the term you are trying to define in the definition itself. This is known as a circular definition. Distinct - The definition should differentiate a data element from other data elements. This process is called disambiguation. Unencumbered - The definition should be free of embedding rationale, functional usage, domain information, or procedural information.

Once you have a great definition, make sure that every class, property, range value and all derived artifacts carry the definitions with it. It is disappointing to open an OWL file, an XML Schema, or a relational database only to see that none of the tables or columns have any definitions and you are left to guess at the meaning.