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Subject: Modelling sessions
Dear all,
Sastry Malladi (Oracle), Simon Laws (IBM), and myself have been involved
in some work for GGF's Data Access and Integration Services (DAIS)
working group, where we attempted to compare different approaches for
mapping DAIS-specific requirements to underlying technologies. We
explored the use of a WS-I only approach, an approach that uses
WS-Context, and one based on WS-RF. (link:
http://forge.gridforum.org/projects/dais-wg/document/draft-ggf-dais-mapp
ings-ggf11/en/1)
One of the questions that were raised during this work was how to model
session-based interactions using WS-RF. I am hoping the members of the
mailing list could help since we didn't reach a concrete proposal on how
this could be done...
Here's the problem...
WS-RF is used to model stateful interactions with resources. Each
message carries some information that identifies the resource behind the
service which should be the logical receiver of the message. I hope my
understanding is correct.
Now, imagine a scenario where we want to establish a stateful
interaction with a service (not the resource) and we want to associate
some quality of service characteristics to it. Let's say, for example,
that we want all interactions within the scope of a particular "session"
to be logged. This would happen irrespective of which resource we are
accessing.
The problem arises if we attempt to model the session as a WS-Resource
and at the same time we want to access another WS-Resource within the
scope of that session. Let's say that we want to drop a database, which
is modelled as a WS-Resource, and we want to log that action. This
causes a problem since it's not possible for both resources to be
addressed within one message.
How do people in this WG recommend we approach this?
There was a suggestion during the discussion we had that WS-RF would be
used to model the database as a resource but additional mechanisms would
be used to model the session (e.g., WS-Context). However, why would
another mechanism be used? Isn't the intention of WS-RF to model all
"resources" that require lifetime management? Isn't a session such a
resource?
So, if the solution is to not use WS-RF, then I would say... what's the
point in defining a common solution when we can't use it in all
situations? If the solution is to use WS-RF to model the session, then
we have the problem of needing to address two resources within on
message.
I'd be grateful for any recommendations from the group.
Here are some pseudo-SOAP messages to help illustrate the problem and
how it is addressed by the other two approaches I mentioned...
WS-I only
---------
<envelope>
<body>
<drop-database>
<sessionId>123</sessionId>
<databaseId>DatabaseA</databaseId>
</drop-database>
</body>
</envelope>
WS-Context
----------
<envelope>
<header>
<context>
...
<sessionId>123</sessionId>
</context>
</header>
<body>
<drop-database>
<databaseId>DatabaseA</databaseId>
</drop-database>
</body>
</envelope>
WS-RF ???
-----
<envelope>
<header>
<sessionId>123</sessionId>
<databaseId>DatabaseA</databaseId>
</header>
<body>
<drop-database />
</body>
</envelope>
Or
<envelope>
<header>
<databaseId>DatabaseA</databaseId>
</header>
<body>
<drop-database>
<sessionId>123</sessionId>
</drop-database>
</body>
</envelope>
Or
<envelope>
<header>
<sessionId>123</sessionId>
</header>
<body>
<drop-database>
<databaseId>DatabaseA</databaseId>
</drop-database>
</body>
</envelope>
Or
<envelope>
<header>
<context>
...
<sessionId>123</sessionId>
</context>
<databaseId>DatabaseA</databaseId>
</header>
<body>
<drop-database />
</body>
</envelope>
Or
<envelope>
<header>
<sessionId>123</sessionId>
<databaseId>DatabaseA</databaseId>
</header>
<body>
<drop-database />
</body>
</envelope>
Of course the last one seems to be completely wrong. However, I can't
see which of the other ones would be the preferred approach. Is there
another way I can't think of?
The combination of ws-context and ws-rf comes close to be the preferred
one but then the question arises on why isn't the session modelled as a
WS-RF since it has lifetime-related requirements. We could probably come
up with other situations where a similar situation arises and where
WS-Context cannot provide us with a solution.
Please note that it is not in my intention to try and cause problems. I
am just trying to better understand the proposed approach while hoping
that this would be a useful discussion to the members of this WG.
Regards,
--
Savas Parastatidis
http://savas.parastatidis.name
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