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RE: [higgins-dev] Sub-contexts
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I guess I am a little slow to learn but...
The root/meta context is a NamedGraphSet and all sub-contexts cannot also be NamedGraphSets (some of which contain exactly one NamedGraph) because a NamedGraphSet cannot contain NamedGraphSets?
Regards,
Michael McIntosh
VP Development
Azigo
-----Original Message-----
From: Sergey Lyakhov [mailto:slyakhov@xxxxxxxxxxxxxx]
Sent: Wednesday, May 26, 2010 9:21 AM
To: Mike McIntosh
Cc: Higgins (Trust Framework) Project developer discussions; Paul Trevithick
Subject: Re: [higgins-dev] Sub-contexts
Mike,
> I know this seems obvious to those of you that are elbow deep in this stuff but...
> Why do we want to prevent sub-contexts of sub-contexts?
Because it is not possible for NamedGraph to contain another NamedGraph.
We are going to use the following mapping:
> a) Context to NamedGraphSet interface.
> b) SubContext to NamedGraph interface.
and NamedGraphSet is a collection of NamedGraph.
Thanks,
Sergey Lyakhov
On Wed, 26 May 2010 05:41:56 -0700
Mike McIntosh <mmcintosh@xxxxxxxxx> wrote:
> I know this seems obvious to those of you that are elbow deep in this stuff but...
> Why do we want to prevent sub-contexts of sub-contexts?
>
> Regards,
> Michael McIntosh
> VP Development
> Azigo
>
> PS: I really wish outlook made it easier to track who made what comment when comments are embedded in responses...
>
> From: higgins-dev-bounces@xxxxxxxxxxx
> [mailto:higgins-dev-bounces@xxxxxxxxxxx] On Behalf Of Paul Trevithick
> Sent: Tuesday, May 25, 2010 7:03 PM
> To: Sergey Lyakhov
> Cc: higgins-dev developer discussions
> Subject: Re: [higgins-dev] Sub-contexts
>
>
> On May 24, 2010, at 12:06 PM, Sergey Lyakhov wrote:
>
>
> Paul,
>
>
> 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.
>
> As I undersntand, we should use the following mapping for NG4J interfaces:
>
> a) Context to NamedGraphSet interface.
> b) SubContext to NamedGraph interface.
>
> NamedGraphSet is just a collection of NamedGraphs, so, it is not
> possible for a SubContest to contain its own SubContexts (only a "root" Context can contain SubContexts).
>
> As a result, I would propose:
> 1. rename the current IContext interface to something like IBaseContext interface.
> 2. add ISubContext interface extends IBaseContext interface.
> 3. add IContext interface, that extends IBaseContext, with the following methods:
> a) Iterator getSubContexts();
> b) ISubContext getSubContext(URI subContextID) (where subContextID is
> a name of an appropriate graph);
> c) ISubContext addSubContext(URI subContextID);
> d) ISubContext removeSubContext(URI subContextID);
> e) ISubContext contextualize(entityid, attributes[]);
> f) void contextualize(entityid, attributes[], ISubContext) - moves
> attributes into passed subcontext;
>
> BTW, because NamedGraph can contain a separate triplets, we can add
> the following methods to contextualize an individual value: g)
> ISubContext contextualize(IEntity, IValue);
> h) void contextualize(IEntity, IValue, ISubContext).
>
> Looks good.
>
>
>
>
>
>
> 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 do not understand how to use named graphs to attach metadata. Of
> course, we can "mark" any separate triple with its graph name. But how
> are you going to attach metadata to that graph? Can you provide me with an example of such metadata?
>
> Here is an example. Imagine there are two h:correlation links:
>
> :Foo
> h:correlation :Bar, :Baz;
>
> If we put these two links into two separate contexts (C1 and C2) we have:
>
> :C1
> {
> :Foo
> h:correlation :Bar; }
> :C2
> {
> :Foo
> h:correlation: :Baz; }
>
> And now we can attach some metadata about C2. Perhaps we want to say
> that the h:correlation link it contains is Valery's "favorite" link. This can be done in C1 or C2 (or any other sub or main context):
>
> In C1:
> :C1
> {
> :Foo
> h:correlation :Bar;
> :C1
> :valerys-favorite "True"^^xsd:boolean
> }
> :C2
> {
> :Foo
> h:correlation: :Baz;
> }
>
> In C12
> :C1
> {
> :Foo
> h:correlation :Bar;
>
> }
> :C2
> {
> :Foo
> h:correlation: :Baz;
> :C1
> :valerys-favorite "True"^^xsd:boolean
> }
>
>
>
> From the other hand, we could use SubContexts for Access Control.
>
> Yes, sub-contexts are ways to keep things tidy--which to me means
> keeping "metadata" (like access control, change events, provenance, etc) in their own sub-contexts and away from the main data graph.
>
>
>
>
>
> 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.
>
> Actually, we need to write the context from a scratch, because NG4J
> uses absolutely different approach (NamedGraphs/Quards/Triples/Nodes), despite it uses/supports some Jena classes/interfaces.
>
> Also I see the following problems with using NG4J:
> 1. NG4J does not support Jena OntModel interface (at least I not found
> how to work with OWL), only RDF model is supported. 2. We always need to work with Quads, not with a model.
> 3. NG4J uses its own serialization (TriX). In case of JDBC, it
> inferior even to Jena persistence way. E.g., it does not support data length > 2000 symbols. Also, I found a bug in de.fuberlin.wiwiss.ng4j.db.specific.DbCompatibility.
> It does not close DB Statements in case of any SQL error (like long
> data), as a result it can not process any query after the connection
> exhausted the limit of non-closed statements. 4. NG4J does not support transactions (at least I not found how to do that).
>
> This is unfortunate. If it's a lot of work to implement NG4Jena and
> then when we're done we only have a toy implementation that won't even support a limited scale, then NG4Jena seems like a waste of time.
>
> Options:
> 1. Get on the NG4Jena mailing list and ask for advice [We should do this no matter what]
> 2. See if there are alternative open source quad stores with better performance/scalability
> 3. Explore non-relational open source graph data bases (e.g. Infogrid, Neo4j, etc.)
> 4. Use an XDI native store
> 5. Decide to defer implementation of sub-contexts
>
> On (5) above: without sub-contexts:
> * we will have to have explicit links from "regular" objects to "metadata" (e.g. provenance)
> * data & metadata will be mixed together
>
>
>
> Thanks,
> Sergey Lyakhov
>
> On Tue, 6 Apr 2010 18:58:24 -0400
> Paul Trevithick <ptrevithick@xxxxxxxxx<mailto:ptrevithick@xxxxxxxxx>> wrote:
>
>
> 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
>
>
> [1] http://wiki.eclipse.org/Context
> [2] http://wiki.eclipse.org/Context_Data_Model_2.0#Key_Concepts
> [3] http://wiki.eclipse.org/Context_Data_Model_2.0#Relationship_to_RDF
> [4] http://www4.wiwiss.fu-berlin.de/bizer/ng4j/
>
>
