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Subject: xLink namespace declarations in CIQ v3.0/xBRL
Thanks Ram OK. I have not substantiated the claim, but on the assumption Hugh is correct then I think we do indeed have a problem. I think we do need to keep interop at the top of our minds...and particularly with xBRL who are strong candidates to use our schemas. I don't know what is involved in making this change, but before doing so, I think we should approach FIRST W3C Xlink 1.1 WG "hard and fast" to get them to give us a definitive view of how to fix it. They are the root cause of the problem becuase they have not provided normative schema so I think they should take some part of the responsibility in the solution. If they instruct us that going back to TR/xlink is correct then it binds them into an approach that they will think twice about changing later. Cheers Colin (Wallis)..no relation to Hugh Wallis below that I know of!:-) ...<snip>.... While investigating the consequences of requiring external schemas to be included in the DTS for the Dimensions spec, Ignacio produced an example which exposed the following issue which I think is potentially rather serious (although the solution is not difficult from our point of view). Before I go on, however, please note that this topic is NOT a discussion about the Dimensions spec itself but about a deeper issue. In our implementation of the schemas for XLink we have created a schema "xlink-2003-12-31.xsd" which purports to define the namespace "http://www.w3.org/1999/xlink". This consists of a set of global Type declarations and some attribute declarations that use them. In addition we have created another schema "xl-2003-12-31.xsd " which defines the namespace "http://www.xbrl.org/2003/XLink". This second schema references the global type declarations that we created in the namespace "http://www.w3.org/1999/xlink". Now when we take a look at the schemas (attached) produced by the OASIS CIQ TC, which also make use of the XLink spec, we can see that they have done a similar thing, except that they have done it differently. Of particular note is the fact that they have created a schema "xLink.xsd" which purports to define the namespace "http://www.w3.org/1999/xlink" and which consists of a set of attribute group declarations which are then referenced by other schemas in their system. Now when you come to use all of these schemas in one cozy environment you hit upon a namespace definition conflict since the definitions of "http://www.w3.org/1999/xlink" are not the same. If you try to, for example, import the CIQ schemas into an XBRL taxonomy schema (e.g. try XBRL validating instance-B.xml), XBRL processors will fail to schema validate the whole set since they have already decided that the XBRL definition of the "http://www.w3.org/1999/xlink" namespace is what they are going to use and they (justifiably) fail to follow the schemaLocation hint provided by CIQ because of this. I think that both the OASIS TC and XBRL have made the same mistake here - and that is to define something in the "http://www.w3.org/1999/xlink" namespace that does not belong there since the XLink spec does not define either the types or the attribute groups I mentioned. As a result we have prevented interoperability. I believe that both XBRL and OASIS must change their schemas that define the namespace "http://www.w3.org/1999/xlink" to bring them into line with just the minimum that is defined by the XLink spec and then, even if we take slightly different approaches (e.g. use of NMTOKEN vs. token), we should achieve consistency and hence interoperability. It is instructive that this issue has taken until now to surface. Hitherto we have been living in our own world where no other XLink users have managed to come close enough to surface this issue and so there have been no consequences of our misbehaviour in respect of the definition of "http://www.w3.org/1999/xlink". Similarly for the CIQ folks. Once we are agreed on this (changing our XLink schema to make it "legal") I think that we should liaise with the OASIS TC group on the issue (suggesting they change there XLink schema to make it "Legal") as well as with the W3C XLink 1.1 WG (pointing out the consequences of not providing a normative schema for their namespace or at least clear guidance as to how to go about creating interoperable schemas for it) Thanks Hugh Hugh Wallis XBRL International Inc. - Standards Development hughwallis@xbrl.org +1 416-238-2553 Skype: hughwallis MSN: hughwallis@hotmail.com Yahoo IM: hughwallis
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