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Web Services and transactions

From: Dieter E. Jenz <dejenz@bpiresearch.com>
Date: Mon, 25 Jun 2001 06:05:45 -0400 (EDT)
Message-ID: <3B370D1B.6090904@bpiresearch.com>
To: www-ws@w3.org
Hi,

The "transactions" issue seems to be virtually ignored in almost all 
discussions that I am aware of. I'm viewing things from a business 
process management perspective. In that context, Web services are 
typically transactional.

The question needs to be answered how transactions can work in an 
operational environment. I just want to illustrate my point using a 
simple scenario.

Scenario: An activity (business process activity) is a Web Service, 
which is implemented by an Enterprise JavaBean (EJB). With 
container-managed persistence (CMP) the EJB container may independently 
initiate a commit. If the process engine is not implemented as an EJB, 
the Web Service EJB cannot "join" a transaction (i.e. the MANDATORY 
transaction attribute would have no effect), which makes all the changes 
caused by the EJB persistent. If the process engine crashes for some 
reason, it will reestablish a consistent state upon restart, actually 
resulting in the rollback of the activity. However, the activity 
implementation has already committed. Consequently, the process engine 
will schedule the activity for execution, resulting in the duplication 
of work. (It might be able to declare the activity just rolled back as 
"in doubt" and put the activity in "suspended" mode, however).

The above scenario triggers a lot of questions, for example:
- What happens if the process engine is implemented as an EJB? Then, the 
process engine can initiate a transaction, which the activity 
implementation can join. The inconsistency problem may not arise.
- What happens if some activity implementations are EJBs, some are COM 
components, some are ...?

The problem space can become extremely complex, since entire business 
processes can be exposed as Web services. In addition, Web services can 
be composed of other Web services.

WSDL does not provide information on non-functional characteristics of 
the service (e.g. QoS information). Also, there is no way do declare Web 
services as transactional.

The overall goal of Web services, to enable application integration over 
the Internet regardless of programming language or operating environment 
would be severely compromised if it was not possible to solve the 
transactions issue in a satisfactory way. Consider the above scenario: 
just putting in a process engine implemented as an EJB would make a real 
difference.

Are there any practical solutions already available (that I am unaware 
of) or on the way?

Regards
Dieter
Received on Monday, 25 June 2001 07:34:51 GMT

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