Gridbus Workflow Enactment Engine - Grid Computing: Infrastructure, Service, and Applications - page 126

TaskType (extension)

+ attributes

- - - +

tasks task paras

1...

∞

-

executable +

QoSconstraints +

LinkType (extension)

-

Workflow
his is the root workflow
element

-

+

from

- - - -

links link

+

to

0...

∞

+

QoSconstraints

+

paras

FIGURE 5.9 Structure of workl ow language.

5.5.1 Tasks

The element < tasks > is a set of dei nitions of tasks that are to be executed.
Figure 5.10 shows the schema of task dei nition. A task can be a single task
or a parameter sweep task. A parameter sweep task is able to process a set of
parameters. The parameters are dei ned in < paras >. The detailed design
of parameter tasks is introduced later. The element < executable > is used to
dei ne the information about the application, input and output data of the
task. The workl ow language supports both abstract and concrete work-
l ows. The user or higher workl ow planner can either specify the location
of a particular service providing a required application in < service > or leave
it to the engine to identify providers dynamically at runtime. The middle-
ware of the application is identii ed through a service information i le by
the GMD when dispatching tasks.
In the example that follows, task A executes the dock.exe program on
the host bellegrid.com in the directory /services and the executable dock has
two input I/O ports: port 0 (a i le) and port 1 (a parameter value). The
example shows that task A has only one output.

<task name= “A”>
<executable>
<name>dock</name>
<service>
<hostname=”bellegrid.com” />
<accesspoint value=”/services/dock.exe” />
</service>
<input>