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From: "Mattmann, Chris A (388J)" <chris.a.mattmann@jpl.nasa.gov>
To: Keith Cummings <kcumming@nrao.edu>
CC: "dev@oodt.apache.org" <dev@oodt.apache.org>
Date: Thu, 1 Mar 2012 19:59:43 -0800
Subject: Re: Three Workflow questions
Thread-Topic: Three Workflow questions
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Hi Keith,

Thanks for your questions! Happy to answer them below:

On Mar 1, 2012, at 9:54 AM, Keith Cummings wrote:

> Hi Chris,
> I have a few questions that I hope won't take you but a minute or two to=
=20
> answer.  If you prefer I send such questions to the OODT email list just=
=20
> let me know.
>=20
> 1. The example code with the Workflow Manager shows examples of=20
> pre-conditions to tasks.  How do you configure post-conditions to tasks?

In the new wengine-style XML workflow documents, available in=20
trunk with the PackagedWorkflowRepository that came with OODT-70 [1],=20
you specify them with something like this:

		<conditions execution=3D"parallel" type=3D"pre">
			<condition id-ref=3D"urn:npp:MOA_IASI_L1C_Daily"/>		=09
			<condition id-ref=3D"urn:npp:MOA_MHS_L1B_Daily"/>		=09
			<condition id-ref=3D"urn:npp:MOA_AMSUA_L1B_Daily"/>		=09
		</conditions>

Note that the conditions tag block can have an attribute 'type',=20
that you can set to post or to pre. At the moment, it simply reads=20
this, but as soon as the wengine is fully integrated, it will support
pre or post execution of these conditions. That should ship with 0.4.

>=20
> 2. Is it possible to branch a workflow?  If so, can you point me to an=20
> example?

Sure, it's possible even in the 0.1-incubating, 0.2 and 0.3 versions.
The way that you branch a workflow is to:

1. add a simple WorkflowTaskInstance implementation, whose goal
is to send an Event *back* to the same workflow manager, to kick off
another workflow. You can find a simple example of such a redirector
here [2].

2. wire up an event for the next stage of the branch to kick off the=20
branch workflow. So, if you had a simple workflow:
       =20
      ----> t2---->t4
t1-/              =20
     \
      ---->t3

You could support this with the following:

w1: t1, branch redirector (seeded with e2,e3)
w2: t2, t4
w3: t3

e1: w1
e2: w2
e3: w3

Where w=3Dworkflow, e=3Devent, t=3Dtask

That make sense? If you need to fan in, you can support=20
this with a precondition on the incoming fan task, holding until
the other tasks in the workflow have finished, and then going.

>=20
> 3. How do you interrupt a workflow from within?  Externally, you can=20
> just issue a stop command on the command-line for this workflow.  If a=20
> task (in the Java code) found that an error condition occurred, how=20
> could that be communicated back to the workflow manager?  (I found that=20
> throwing an Exception does the trick, but I was wondering if there was a=
=20
> less obtrusive way to signal the workflow to stop.)

You can, inside of a WorkflowTaskInstance, do something like:

XmlRpcWorfklowManager wm =3D new XmlRpcWorkflowManager(new URL(met.getMetad=
ata("WorkflowUrl"));
wm.stopWorkflowInstance(met.getMetadata("WorkflowInstId"));

That will basically have the same effect as the external stop. Exceptions w=
ork fine too,
even if they don't look elegant :)  Would be nice to have a WorkflowStopped=
Exception, which extends
some generic WorkflowTaskInstanceException, but for now, a good ol' Excepti=
on will do it itoo.

HTH!

Cheers,
Chris

[1] https://issues.apache.org/jira/browse/OODT-70
[2] http://s.apache.org/NeK

++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Chris Mattmann, Ph.D.
Senior Computer Scientist
NASA Jet Propulsion Laboratory Pasadena, CA 91109 USA
Office: 171-266B, Mailstop: 171-246
Email: chris.a.mattmann@nasa.gov
WWW:   http://sunset.usc.edu/~mattmann/
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Adjunct Assistant Professor, Computer Science Department
University of Southern California, Los Angeles, CA 90089 USA
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++