[SAGA-RG] Service Discovery spec updated at last ...

[Steve Fisher]

> In the attached version, I tried to address the things we
> agreed upon, and changed the service types/names table as
> proposed.  Could you give it another pass, please?
> I left the Constructors untouched for now, until we agreed
> on something, ok?
>
> Also, there is a question from me at the bottom of page 5:
>
>  "Note: Why not TimeOut, AuthorizationFailed, etc??"

For the discoverer constructor, I guess the Authentication exception
can be thrown if you don't pass in a session or if you pass in what
used to be a valid session that has since expired. How would you class
that one?

Unfortunately quite a lot of the allocation of exceptions is
implementation dependent. It would be better to be able to just throw
a Security exception - but that is not an option as it is not in the
core spec. If you need to get authenticated this could result in a
timeout if contact with some remote server is required.

In our current implementation, list-services does most of the work and
so can throw timeouts and could throw security errors except that we
happen to connect to a non-secured information service. However the
subsequent calls (such as get_data) can throw the same exceptions as
they could choose to go back to the information service to pick up
information that was not originally needed when making the selection.
If we don't allow the possibility to throw these exceptions the
implementation is needlessly restricted. This is why I like the
NoSuccess everywhere. In other words I would use NoSuccess for those
conditions which are implementation dependent - which in this case is
quite a lot. For example you have added DoesNotExist for the
constructor - implying that the API would contact the underyling
information service. However there is no reason why it should do so at
this stage.


> Nothing is ever easy.

I am inclined to agree

Steve