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Notes on the discussion about the external tool at the Debian Med meeting 
during January 2011.

== External tool invocation discussion ==

Ways of calling tools are described by "use case descriptions".  The use case 
descriptions can be held in a registry.  For example,

[[http://usecase.taverna.org.uk/sharedRepository/index.php]]

The KnowARC project developed a plugin for Taverna that can read the use case 
descriptions and allow you to include calls to the a tool in a workflow.

You need to know how/where to call the tool - the "invocation mechanism".  
There are currently three options for the invocation mechanism:

 * local
 * ssh to specific machines (uses Taverna's credential manager to keep the 
login information confidential)
 * on a KnowARC grid

In the current plugin, the setting for how to call the tool is shared by all 
external tool services in a workflow e.g. all the tools are run locally.

=== Planned improvement ===

Taverna will manage a set of invocation environments that are named and 
identified by a UUID, for example "fred" and 
"62A81F2F-4C3D-4C0C-ACF1-681327130328".  (The UUID may be changed to being a 
URL.)

An external tool service in a workflow will state the invocation environment 
that the tool will be run in.

The invocation environments can specify the settings for the various invocation 
mechanisms and also which invocation mechanism is currently to be used e.g. ssh 
goes to phoebus.cs.man.ac.uk but to currently use local.  So you can have some 
services using environment "fred", some "bob" and some "jim".

The invocation environment manager allows users to edit the settings and also 
change which mechanism to use.  This allows you to easily change where a set of 
tools will be run e.g. to change all services using setting "bob" to run 
locally.

There is also a proposal to understand the idea of test and production 
invocation environments.  So, "fred" can be set to run services locally during 
test and on a grid during production.  The choice of whether to run a workflow 
in a test or production mode will be made when the workflow is run.

'''It is not clear how the choice of mode will be shown to the user'''

'''A workflow run may vary the data that it uses according to the run mode e.g. 
to use different data during test and production.  There needs to be explicit 
support for this in the workflow but it is not clear how.'''

=== Ongoing issues ===

 * ssh equivalent for windows.

== External tool description ==

There is an XML format for specifying the use case descriptions.  We have also 
looked at:

 * acd as used by EMBOSS and SoapLab
 * Galaxy
 * BioPieces
 * GIMIAS
 * BOINC

Current plan is to be able to translate the EMBOSS acd descriptions and put 
them in a repository.  Future work will be done to ensure that the external 
tool capability is sufficient.

== Additional invocation mechanisms ==

For Taverna 2.3, we will include local and ssh invocation as part of the 
release.  The KnowARC invocation will probably be made available as a plugin.

Need to look at cloud invocation soon.

== Invocation environment checking ==

There is currently some limited ways of specifying what needs to be on the 
machine where a tool will be run, and also how to check if the tool can be run 
there.  Need to look at more general ways of specifying this.

== Sensible handling of data ==

Want to minimize the transfer of data.  So data stays, where possible, with the 
tools that will use it.  Also, tools are invoked where the data is.

Need to extend Taverna's data handling mechanisms to deal with this.  Need to 
improve some of the invocation mechanisms to better decide where to run the 
tools.

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