SOA may mean different things to different people (to me, SOA is just an
architectural style), but one thing is certain – SOA is being touted as the next
generation enterprise integration technology and architecture. And yes, SOA is
not all about Web services; however, Web services (SOAP and WSDL specifically)
are immediately brought into conversation when SOA is mentioned.
But do Web services today provide necessary enterprise-level capabilities?
Take transaction support. Ideally, we should be able to wrap any access to a
remote resource in a transaction since remote resources are prone to failing. In
J2EE , this is certainly supported for JMS , JDBC and RMI . Yes, two-phase
commit comes at a price, but it‘s nice to have it available when it‘s needed.
Now, SOA is all about remote calls (synchronous or asynchronous, does not matter).
So where is the transaction support? Well, there is WS-AtomicTransaction
specification that in theory should provide it. But where are the products that
support it today? Also, this specification is not currently part of any WS-I
profile, so interoperability is a big question.
WS-ReliableMessaging is in the similar situation, and so the rule of thumb today
is that Web services should conform to WS-I basic profile, which does not
include any of the advanced specifications.
In theory, one could use SOAP over JMS supported by many J2EE vendors today
which immediately makes SOA implementation more robust. But this approach is
hardly interoperable with non-Java technologies and what is it really buying for
J2EE applications? JMS is already an abstraction of the messaging middleware, so
why do we need another abstraction on the top of it?
I concede that describing JMS destinations using WSDL might be useful for some
environments, but in many cases it is simply overkill (if you must use BPEL ,
use the BPELJ variant which directly supports JMS ).
Using JAX-RPC or WSIF to communicate with JMS does not sound like a good idea
either. These APIs are not JMS -aware, so, for example, how do I get/set
messageID or correlationID?
I do realize that developing true enterprise-level integration technologies
takes time, and so perhaps in a couple years most Web services products will
provide WS-Transaction and WS-ReliableMessaging support out of the box. But are
Web services really ready to take on the enterprise today?