RE: Web Services and transactions

Well, I think I will let this one go  - I agree that a more relaxed attitude
to ACID transactions is required but this does not preclude the use of 2PC.

There is no reason that a relaxed peer to peer structure for transaction
coordination could not use 2PC, basically all participants are equal peers,
except one peer either plays the role of initiator and coordinator( as well
as participant ). The classic rule of peer to peer follows the "orwelian"
theory that all are equal, just that some are more equal than others!

Regards
Mark Potts


-----Original Message-----
From: Satish Thatte [mailto:satisht@microsoft.com]
Sent: Monday, June 25, 2001 8:02 PM
To: mark.potts@talkingblocks.com; Adam Bosworth; www-ws@w3.org
Cc: Henrik Frystyk Nielsen; Johannes Klein
Subject: RE: Web Services and transactions


I am not a transactions expert but I asked some local experts and the
opinion was that although 2PC is a classic agreement protocol that could
be used for long running transactions (LRTs), the realities of
implementation tradeoffs based on current 2PC practice with databases
make 2PC too constraining for LRTs, and a more relaxed peer-to-peer
protocol might be desirable.

-----Original Message-----
From: Mark Potts [mailto:mark.potts@talkingblocks.com] 
Sent: Monday, June 25, 2001 3:13 PM
To: Satish Thatte; 'Adam Bosworth'; www-ws@w3.org
Cc: Henrik Frystyk Nielsen; Johannes Klein
Subject: RE: Web Services and transactions

Satish

While I agree whole heartedly with the need for a protocol that supports
bit
loosely coupled and more tightly coupled services, I think its important
that 2PC is treated in any discussion about transactions as a protocol.
2PC
defines a protocol for coordinating participants that have enrolled into
a
transaction  - this could just as well be used as a protocol where the
levels of isolation and durability are relaxed, in the case of
compensating
transactions.

Regards
Mark Potts

-----Original Message-----
From: www-ws-request@w3.org [mailto:www-ws-request@w3.org]On Behalf Of
Satish Thatte
Sent: Monday, June 25, 2001 2:15 PM
To: Adam Bosworth; www-ws@w3.org
Cc: Henrik Frystyk Nielsen; Johannes Klein
Subject: RE: Web Services and transactions


Adam,

I think you are agreeing with me so you probably aren't missing anything
;-)

But web services will not always be used in the loosely coupled mode, so
there will be need for 2PC-like behavior in specialized circumstances.

In any case a distributed agreement protocol for web services is
probably needed for both tightly and loosely coupled business
transactions.

Satish

-----Original Message-----
From: Adam Bosworth [mailto:adambos@crossgain.com]
Sent: Monday, June 25, 2001 11:12 AM
To: Satish Thatte; www-ws@w3.org
Cc: Henrik Frystyk Nielsen
Subject: Re: Web Services and transactions

It is worth noting that supporting ACID distributed transactions over
Web
Services is very problematic. The very idea of a Web Service is a way to
enable disparate applications built by different organizations, groups,
or
even companies to be able to use services from each other. But it is
highly
unlikely under such circumstances that the outside client of a service
can
typically be trusted to invoke anything that requires locks over any
substantive period of time. In general, the model I'm familiar with for
handling such cases (coming out of long-running transactions and EAI)
has
tended to support compensating transactions and exception handling
rather
than true DTC for these reasons.

It is true that the process engine for any applications that wants to
participate in a "transactional" web service would have to be
implemented as
an EJB, but that is surely internal to the application delivering up
support
for the service (or invoking it) and not the business of the Web
Services
Protocols.

Am I missing something here?

Adam Bosworth

----- Original Message -----
From: "Satish Thatte" <satisht@microsoft.com>
To: <www-ws@w3.org>
Cc: "Henrik Frystyk Nielsen" <henrikn@microsoft.com>
Sent: Monday, June 25, 2001 10:43 AM
Subject: Re: Web Services and transactions


> Dieter,
>
>
>
> The XLANG proposal for business process description includes a notion
of
> long-running transactions which can support nested ACID transactions
and
> compensate for them when needed [1].  This is also available in the
BPML
> process description language developed by BPMI [2].  I agree with you
> that transactions must be addressed in the context of web services in
> general and business processes in particular.  There are two separate
> ways to do it.  One is to build up a transaction coordination
> architecture with the usual 2PC semantics.  This can be problematic
> because of the need to lock resources across service (and hence
> business) boundaries.  Less onerously, one can use explicit
compensation
> as in XLANG.  Both have their place in different circumstances.
>
>
>
> Satish
>
>
>
> [1]  http://www.gotdotnet.com/team/xml_wsspecs/xlang-c/default.htm
> <http://www.gotdotnet.com/team/xml_wsspecs/xlang-c/default.htm>
>
> [2]  http://www.bpmi.org/index.esp <http://www.bpmi.org/index.esp>
>
>
>
>
>
> -----Original Message-----
>
> From: Dieter E. Jenz [mailto:dejenz@bpiresearch.com]
>
> Sent: Monday, June 25, 2001 03:06
>
> To: www-ws@w3.org
>
> Subject: Web Services and transactions
>
>
>
>
>
> 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
>
>
>
>
>
>
>
>
>