Null Code

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The template of an Enumerated Data Type allows optional values to be set for Null Code and Null Meaning.

This adds an extra value to the list of Constrained Values that are drawn from the EDT's Code List and that can be used to signify that none of the Codes from the Code List are applicable (or something similar).

For instance, consider a Code List containing the codes 1, 2, 3, 4, 5, 6, 7 meaning Monday to Sunday. For some applications this is satisfactory as it is. However, in a particular interface between two applications it may be necessary to convey the concept of 'Not specified' while in another interface 'Refused to answer' may be required.

Often, additional codes such as '0' or '999' or 'X' or 'ZZZNMIS' are added to mean 'None of these', 'Not specified' or 'something else that doesnt fit'.

Such codes usually cause problems because:

  • they break the Code Format that applies to the other codes
  • they need special treatment at the receiving end, perhaps to ignore them or store a Null value in the database etc

Thus, Listpoint provides the option to define an additional code (and an optional Null Meaning for it) that does not need to conform to the Code Format rules and can be used to trigger appropriate processing when receiving messages. Such special codes can then be removed from the underlying Code List leaving it as a pure enumeration of disjoint concepts without special cases.

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