Possible policy for default prefixes and terms (relevant for ISSUE-68 and ISSUE-64)

Dear all,

we had the discussions before on whether we should have some default prefixes and terms defined for different host languages. I think we have agreed (I am not sure that we had formally recorded that) that we would have a default profile defined for XML and we certainly have that for *HTML*.

Up to now the default profile contained the set of well known terms for *HTML* plus, as proposed in an issue resolution, described by. However, and this is where this is relevant to ISSUE-68, I firmly believe that we should use the same mechanism to define a set of default prefixes, too. Toby has already proposed that before Harry's comments came in, and I would like to pick this up again as a tool to resolve some of his issues. A typical problem that came up as a complaint many times from Facebook, for example, that authors regularly forgot the namespace declaration, or they forgot the trailing '#'; this made the content erroneous in RDFa.

I have had some discussion with the team (including Harry) on a policy that I have now documented in 

http://www.w3.org/2010/02/rdfa/wiki/DefaultPrefixPolicy

This essentially describes how certain prefixes and terms would become part of default profiles.

Two more comments on the policy:

- We should realize that the profile mechanism, though RDFa specific now, may become attractive for other serializations. I expect the RDF group to look at this for a JSON serialization, for example. We should define the policy in a slightly more general term and use URI-s for mailing list and such that are not RDFa specific
- We could 'bootstrap' the mechanism by setting up the wiki page with a proposed set of prefixes. I would expect foaf, dc, dcterm, gr (good relations), fb (facebook) to be typical examples.

Ivan

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Ivan Herman, W3C Semantic Web Activity Lead
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