Kevin, hello.
On 2010 Sep 22, at 23:23, Kevin Ashley wrote:
> Norman Gray wrote:
> ....
>
>> The idea of AGAST is that you develop an ontology of your data -- which could
>> potentially be based on a formalised version of the model you might have
>> already for OAIS purposes, say.
> Thanks for bringing this to my attention - it looks like something we at
> the DCC should be drawing attention to.
Thanks. I'd very much ilke to build on this work, and I think it could go in interesting directions, so I'm keen to talk to people.
> If my quick reading of it is correct, I think the one area where it doesn't
> fit the NDAD model is that where the restriction applies to part of an object.
> The X.812 model you refer to implies access decisions are made at the object
> level and access is or is not granted to an object. Where the restriction is at
> the level of a database cell or a rectangle of pixels on a page, this model
> becomes expensive to apply (since you need to treat cells or pixels as objects
> and ask for decisions about each of them.) We took the approach that at this
> level, the ADF invokes the object access function but passes across information
> which an embedded AEF interprets as it grants access to the object, blanking
> out pixels, rows, columns, cells, segments of video, etc.
That's correct: what we described applies only to objects and, as you remark, it would potentially be expensive to regard individual rows as objects.
However 'is user X allowed access to object Y?' isn't the only question you could ask of the ontology. You could also ask 'is user X in the class of people who should be given redacted access?'. That would mean that the AEF could deem that to be 'access granted' in an X.812 sense, but know that it has to do a redaction before it passes the results to the user, just as you describe.
That is, although the paper illustrates only yes/no queries (specifically SPARQL 'ASK' queries), it's built on a flexible query language which allows you to ask very different types of question about the object and the access attempt, if that's useful to you.
Best wishes,
Norman
--
Norman Gray : http://nxg.me.uk
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