Introduction to the WS-PGRADE/gUSE Science Gateway Framework - Science Gateways for Distributed Computing Infrastructures - page 23

Fig. 2.2 The three generic workflow development phases in WS-PGRADE

2.5.2.1 The Editing Phase: Creation of the Work ow Graph

The users construct their abstract work ows in this phase. Practically, it covers the

work ow graphical designer and

visualizer tool, the Graph Editor of WS-PGRADE (Fig. 2.3 ). The structure of WS-
PGRADE work

ow graph creation by the interactive, online work

ows are represented by directed acyclic graphs (DAGs) as shown
in Fig. 2.3 . The DAG-based structure is the static skeleton of a work ow in WS-

PGRADE. The nodes of the graph are abstract represenations of jobs (or service
calls). Each job must have a name, and job names are unique within a given
work ow through input

and output ports. An output port of a job connected to an input port of a different
job is called a channel. Channels are directed edges of a graph, directed from the
output ports toward the input ports. A single port must be either an input or an
output port of a given job.
A job in a work

ow. The job communicates with other jobs of the work

ow may have single and parametric input ports (which should

be speci ed in the next, the con guring phase of work ow development when

concrete work ow). If a node has only single

input ports, it is executed only once as a single instance processing the single inputs
of every input ports. These nodes are called normal nodes. If a node has at least one
parametric input port it is called parametric node. If a parametric node has one
parametric input port, it will be executed in as many instances as the nukmber of

ow is de ned from abstract work

files that arrive on the parametric input port (Manual 2014).