TAP information schema

[Doug Tody]

On Thu, 11 Oct 2007, Keith Noddle wrote:
> 
> - SOAP or REST?
> - Synchronous?
> - Asynchronous?
> - If asynch:
>   - how do we handle return of results?
>   - VOSpace?
>   - Staging?
>   - What are the issues for either?
> - etc

Ignoring for the moment the metadata query issue, my impression from
discussions over the past year or so is that we already have consensus
on most of the above issues.  In short:

    - The basic interface should be REST-like (consistent with the
      other DAL interfaces unless there is good reason to diverge),
      ideally defined in such a way that the logical protocol is
      separate from the transport and could be layered upon other
      distributed computing platforms in the future, such as SOAP.

    - Async is required for fully-functional services; it probably
      should be required for advanced capabilities such as multi-region
      queries, complex or large queries, etc. (in other words, require
      async to be able to do these things).

    - Sync (when it works) is *much* simpler for both the service
      implementation and the client, and is adequate for many simple
      queries including small queries of a single table (which can
      normally stream) and metadata queries.  We should provide
      for this, with an indication of overflow or other failure
      condition; async would ultimately be required in this case,
      service capabilities permitting of course.  Simple service
      implementations should not be required to implement async, but
      a "fully compliant" service (as any major data center should
      provide) implements async.

    - If large amounts of data need to be managed, as well as for
      full functionality (e.g., workflows where remote delivery of 
      results is required) VOSpace should be used.

There are many details to be worked out of course, but I think
there is consensus on the above (if anyone disagrees please say so).
Key issues for which there is not yet agreement are on the content
and handling of table metadata queries, and whether a "simple query"
capability is required (for data; most would agree it probably is
required for metadata).

	- Doug