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[higgins-dev] Sub-contexts
Folks,

I strongly believe that we should add sub-contexts (within a parent context) to the CDM. I have updated the definition of Context [1]. I copy the key bit here (from "CDM 2.0" onwards):
  • Is a set of one or more Entities
  • Is a special kind of entity identified by a ContextId
  • Have zero or more Attributes.
  • Has a schema (ontology) that describes kinds of Entities and Attributes that an instance of this Context contains.
  • Has its own security and access control policy
  • CDM 2.0: May (strictly) contain zero or more sub-Contexts. A sub-Context is a Context with these restrictions:
    • It is entirely contained within its parent Context
    • Its set of entities is any subset of its parent's set of entities.
    • Inherits its schema from its "parent" context
    • Inherits its security and access control policy from its "parent" context
I have also updated the bullet on Contexts here [2]. And I have updated these paragraphs [3].

IMPLICATIONS

(1) Enhancement to IdAS.

We have to add to IdAS API the ability to add/find/delete a sub-Context within a Context. I hope SergeyL can suggest a straw man change. The good news is that our main CP on the PDS (aka Attribute Service) backend is backed by Jena. And there exists a version of NG4J [4] that already supports the necessary semantics.

I think (for convenience) we should add a new API called "subcontext = contextualize(entityid, attributes[])" that would take an entity and zero or more of its attribute type URIs (and we need to specify down to the individual value level too) and move them into a subcontext and return the id of the subcontext. Maybe we need a simpler "move" method too in case the subcontext we want to move stuff into already exists.

What I like about this change to IdAS is that it is really clean. We don't have to introduce "Statement" classes (triples, etc.) into the IdAS API. The contextualize method is all we need. After that we're back to Contexts, Entities, Attributes and Values all over again.

(2) Statements about Statements

With sub-contexts (and esp with the contextualize() method) we now have a way of taking statements being made in one context (or sub-context) and moving them into a sub-context. Since this sub-context itself has an entityid we can attached attributes to it ("inside" the subcontext so to speak) or we can make statements where the value (RDF object) is the subcontext ("outside" the subcontext in the main "dataset" context).

Valery (and I think Vitaliy) had wanted a way to associate metadata with h:correlation links from A to B (across contexts c1 and c2). With sub-contexts this is now easy. You just move (contextualize()) this one entity-attribute-value triple from the default (main) context to the sub-context. Now you can attach whatever attributes to the sub-context you like.

I had proposed that we handle password history in a password specific way. But after talking with Mike, I'm re-thinking (yet again) if we could implement history metadata in a 100% generic ( non-pwmgr-specific) way.

(3) More similar to XDI

With this change we make supporting XDI easier. This will be important because there is a move afoot to sort of standardize data sharing using XDI.

--Paul


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