2746 2006-01-20 21:26:28 +0000 wd-20: Identity vs. Equality in enumerations and fixed value constraints 2006-01-20 21:27:49 +0000 1 1 1 Unclassified XML Schema Datatypes: XSD Part 2 1.1 only PC Windows XP RESOLVED WONTFIX P2 normal --- 1 holstege cmsmcq www-xml-schema-comments oldest_to_newest 7910 0 holstege 2006-01-20 21:26:28 +0000 In the call today we decided to use identity for value constraints, just as we do for enumeration, on the logic that a fixed value constraint is like an enumeration with a single value. Noah and I expressed a certain discomfort with identity in both these cases, especially with respect to precision decimal. Consider: <xs:simpleType name="u2numbers"> <xs:restriction base="xs:precisionDecimal"> <xs:enumeration value="1.0"/> <xs:enumeration value="2.0"/> <xs:enumeration value="3.0"/> <xs:enumeration value="14.0"/> </xs:restriction> </xs:simpleType> We accepted that "1" and "1.00" would not be valid against this enumeration on the grounds that enumerations of decimals were not used in practice, so this infelicity was unlikely to bite anyone. The work-around would be to enumerate a sufficient range of precisions to cover the most likely cases to turn up in practice: <xs:simpleType name="u2numbers"> <xs:restriction base="xs:precisionDecimal"> <xs:enumeration value="1"/> <xs:enumeration value="1.0"/> <xs:enumeration value="1.00"/> <xs:enumeration value="2"/> <xs:enumeration value="2.0"/> <xs: enumeration value="2.00"/> <xs:enumeration value="3"/> <xs:enumeration value="3. 0"/> <xs:enumeration value="3.00"/> <xs:enumeration value="14"/> <xs:enumeration value="14.0"/> <xs:enumeration value="14.00"/> </xs:restriction> </xs: simpleType> Painful in practice, impossible in the general case (although I suppose you could enumerate to the limits of precision supported by your processor, urgh.) Or you put in a pattern facet instead, which can also be painful. Consider this definition: <xs:element name="meterMin" type="xs:precisionDecimal"/> Somewhere in a content model: <xs:element ref="meterMin" fixed="1.0"/> In this case<meterMin>1.00</meterMin> and <meterMin>1</meterMin> would be rejected. Here, however, there is no workaround that allows you the simplicity of using the fixed attribute: you have to change the type. If you wanted to have different fixed values for different uses of the element meterMin in your schema, you have to jump through some rather painful hoops using local definitions that have nasty enumerations or patterns in them: the type of each use of meterMin would have to be different.I still question the wisdom of using identity in either of these cases. Most types do not distinguish identity and equality, and in those cases that do, the results are unhelpful, as shown. Request concerning Part 1 Transition history raised on 3 Dec 2004 by Mary Holstege (http://lists.w3.org/Archives/Public/www- xml-schema-comments/2004OctDec/0026.html) declined on 3 Dec 2004 (http://lists.w3.org/Archives/Member/w3c-xml-schema-ig/ 2004Dec/0002.html) RESOLVED No consensus to change status quo. Acknowledgment cycle announced by group on 3 Nov 2004 (http://lists.w3.org/Archives/Member/w3c-xml- schema-ig/2004Nov/0002.html)