Code list model and implementation requirement: Unambiguous identification

["G. Ken Holman" <gkholman@CraneSoftwrights.com>]

As a technical requirement code lists must be unambiguously identified, 
such that:

   (1) - any two uses of the same URI represent the use of the very same 
code list definition

   (2) - no two differing code list definitions shall be represented by the 
same URI

The business issue is that when when two trading partners identify the use 
of a code list, there must not be any ambiguity.  Should either partner 
create a code list or change an existing code list, the identification of 
the resulting code list must be distinct from that of its origin.

Note: for implementation considerations, Gunther has suggested the approach 
of namespace URI fields for code list supplemental identification values in 
draft-stuhec-codeListNamespaces-0p2.doc ... the "ripple effect" of this 
ensures that when non-UBL code lists are in use, non-UBL namespace URI 
strings must be used (because the UBL-standard W3C Schema fragments must be 
changed to utilize the non-standard code list URI strings).  This 
guarantees the unambiguous identification of the entire schema and two UBL 
partners who are using the same namespace URI for a UBL schema are 
guaranteed to be talking about the identical element and attribute 
structures and code list definitions.

In contrast, original proposed UBL approaches to storing code list 
supplemental identification values in defaulted attributes can "hide" 
changes in such a way that two uses of the same namespace URI string would 
not represent the identical *complete* schema definition.  This ambiguity 
could produce interoperability problems.

.................... Ken

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G. Ken Holman                 mailto:gkholman@CraneSoftwrights.com
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