What are the rules for changing the mandatory status, conformance condition, and or multiplicity of attributes and associations?
Specifically, the document reads as follows today: "Attribute conformance can be changed from Required to Mandatory, and from Optional to Required, but not the reverse."
In balloting the following commment was received: "2 issues with this bullet point: 1) It sounds like the opposite of v2 which should be explained. In v2.x (see Chap 2, section 2.8.2) optionality can only be tightened (Existing optional fields may be made conditional or required). Seems like there should be some correlation. 2) Formal English should be used."
See also Semantic Backward Compatibility
January 17, 2010, Q3 The rules for what changes constitute backward-compatible changes and which constitute substantive change are documented in the HL7 Version 3: Substantive Change document in the HL7 Ballot Package under the Background Documents section