Data Access Scope.

[Mario Antonioletti]

Hi,
   I was thinking round some comments that Allen wrote on the section I
distributed yesterday and became somewhat confused as to what the scope
of data access is for this ogsa data architecture document. I make some
assertions below and some of the consequences - any thoughts? What
should be ruled in scope and what is out of scope for this version of
the document?

			Mario

---

Assertions:

1. a data service represents:

     i)   A single data resource (the data resource may be arbitrarily complex,
          e.g. it could be a federation but the data service has a single point
          of contact with the data resource)
     ii)  More than one data resource
     iii) More than one data service
     iv)  A combination of data resources and data services

2. the data service's data access capability allows:

     i)  Read only access.
     ii) Read and Write access.

3. data obtained by a data service through a data resource is:

     i)   Returned directly back to the client
     ii)  Materialised and kept at the service side, exposed through
          another (or the same) data service.
     iii) Data is delivered to a third party, the client gets a status
          notification.


Consequences:

1. For cases 1 (ii)-(iv) require some naming scheme for the service to
   determine what data resource/service can be targetted assuming that
   a message will only ever target a single resource. Most of the
   entities will have names that already exist.

Question: can/should a message be able to target multiple resources?

2. For cases 1 (iii) and (iv) require some service-to-service access
   mechanism. Is this in scope for data access.

3. For case 2 (ii) Write access will complicate things by a
   *lot*. Things get even more complicated if cases 1 (ii)-(iv) which
   may require to operate in some transactional context.

4. For case 3 (i) is kind of weak for transferring large amounts of
   data.  Are cases 3 (ii) and (iii) in scope for data access? You
   could have an operation that specifies another end point (which
   need not be a service) to which data should be delivered. Is this
   in scope?

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|Mario Antonioletti:EPCC,JCMB,The King's Buildings,Edinburgh EH9 3JZ.   |
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