Activation Criteria for Attribute resolvers

[Rod Widdowson]

I was going over attribute-resolution-api prior to passing it over to Tom
for refactoring, when I happened (yet again) on IDP-280 : "Define Syntax
for, and add parsers for the ActivationCriteria inside the Attribute
Resolvers" (although it applies to data connectors as well).

Do we have any idea how we might want to wire this up?  What are the sorts
of predicates we might want to use?  Do we want to think in terms of a
similar predicate language to that used in filtering?

I could see that there might be use for a predicate which says "Only resolve
this data connector if the SP is such and such" and so forth, particularly
if it was considered that the act of resolution might be particularly
heavyweight (big slow remote database lookup).    Of course a similar result
can be achieved by filtering.

With a stretch of imagination I could see repurposing all (or many) of the
"natural policy rule" Match Functors (or at least those which only care
about the AttributeRecipientContext), but I'd be worried about circularity
of reference and also downright frightened of the Schema changes (how do you
capture that "AttributeIssuerRegexpPolicyRule" is OK as an activation
criteria, but that "NumOfAttributeValuesPolicyRule" isn't).

Or can we leave this case on the shelf for a while - it isn't going
anywhere.

/Rod