Introduction to the WS-PGRADE/gUSE Science Gateway Framework - Science Gateways for Distributed Computing Infrastructures - page 24

Fig. 2.3 Directed acyclic graph-based structure of a sample workflow in WS-PGRADE graph

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ow type also supported by WS-PGRADE/
gUSE is the so-called parameter sweep or parameter study (PS) work

A special but widely used work

ow, which is

typically used for simulations where the same simulated work ow should be

executed with many different input sets. DCIs are ideal for PS executions, and
therefore their most frequent usage scenario is performing such PS work ows.

A typical PS-work ow contains three nodes (jobs) as shown by Fig. 2.4 :

1. the generator job generates the necessary parameter set;

2. the parametric job (this is the call job in the example of Fig. 2.4 ) executes a

speci c application in as many instances as there were outputs generated by the

generator job; and,

3. the collector job collects and processes the results of the parametric job (for

example, by creating statistics based on the results of the different executions).

If the output port of a generator job is connected to the parametric input port of a
parametric job, then this parametric job will be executed for every file generated by

the generator job.
Another useful charateristic of WS-PGRADE work ows is the possibility to

embed work ows into work ow nodes. Thus, instead of running, for example, an

executable inside a work ow node, another WS-PGRADE work ow may run

inside the parent work ow node. To embed work ows, users need to apply

work ows created from the so-called templates. A template is a generic work ow

where some con guration parameters are fixed. It can be used to serve as a base of

ows. 6 creating the de nitions of new work

6

The gUSE work ow concept is discussed in detail in Chap. 3 .