[mdx] GH issue 3: lookup based on entity attributes

[Ian Young]

This is, I think, the only remaining thing we need to have a discussion thread for.

Leif's GitHub issue:

https://github.com/iay/md-query/issues/3

That just references this mail thread from May 2011:

http://lists.iay.org.uk/pipermail/mdx-iay.org.uk/2011-May/000141.html

> Today the MDX query string supports a simple query syntax.
> 
> mdx-url = url-prefix '/' query
> query = 1*(tag '+') / entityID / hash(entityID)
> 
> Increasingly entity attributes are used to add context to
> EntityDescriptor elements and it would be nice to have a way
> to query for those.
> 
> I propose the following: allow a tag to be formatted according
> to one of
> 
> (1) '{' name-format '}' name '=' value
> (2) name '=' value
> (3) value
> 
> In case (2) name-format is assumed to be
> 
> urn:oasis:names:tc:SAML:2.0:attrname-format:unspecified.
> 
> and in case (3) - which is the original 'tag' case we just have
> to define a common attribute for social 'tags' on metadata. This
> is something that needs doing anyway. Since we would be using the
> unspecified name format we could simply define the attribute name
> 'tag' as the attribute name used for tags.


There was some discussion at the time (read the thread) of what we were referring to here, because "entity attributes" has both an informal and a formal meaning, the latter being a SAML-specific construct.

The usual question needs to be: is there a near-term, concrete use case for this ability, or does having the responder assign an identifier to an arbitrary collection suffice for the moment?

I'm hoping for the latter (from the same reasoning as the intersection operator), so that we can drive the current text towards something stable in the next week or so. I'd very much like to throw up a new I-D at that point and flip from spec mode into implementation mode for a while, so that we can get a feel for what might be missing.

	-- Ian



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