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From "James Strachan" <james_strac...@yahoo.co.uk>
Subject [workflow] comparing web based and message based (was Re: Workflow)
Date Wed, 14 Nov 2001 10:50:41 GMT
Hi Colin

Just a few thoughts about using the Workflow project with JMS.

I think there are close parallels between a web application receiving HTTP
GET/POST requests with a body, headers & parameters and with a web
application receiving JMS messages with a body, header & properties. Its one
of the main reasons why the Messagelet Engine came into being in the
Messenger project.

However the current Workflow project looks like its first focus is a typical
web application scenario, where there is a single web application JVM, using
HTTP Sessions, performing *all* the steps. As each HTTP request is received
the HTTP Session can be used to share information across related requests.
In a typical JMS / MOM based workflow system, each step is often a totally
seperate process - or even a totally seperate cluster of processes, maybe
even implemented with different technologies.

This is similar to having a web-application workflow where steps can be
processed in totally different web applications (and possibly server farms)
and so session information gets lost across steps. I know of a few companies
who are starting to vertically align their web applications based on
business function so can imagine workflows across web applications and
server farms being useful to some folks.

I wonder how important is the HTTP Session state in the current workflow
project - I guess its kinda crucial? Or can it work in a relatively
HttpSession-less way by keeping all the state in the <form>s as hidden
fields or using a database?

For MOM-based workflow we'll either need to ensure all state is sent with
the message or that we use some other distributed state mechanism, like
databases, so each step can persist its state for further steps to use.

I guess many of these issues are common to both web applications (when using
server farms and multiple web apps) and for JMS based workflows.

Thoughts?

James


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