Gridbus Workflow Enactment Engine - Grid Computing: Infrastructure, Service, and Applications - page 132

hread

WorkflowCoordinator

WorkflowModelToDiGraph

XMLParsingToModel

11..n

DiGraph

WorkflowModel

JobMonitor

TaskManger

1..n

1..n

1..n

1..n 1..n

GraphNode
children : List
parents : List

Job

DataConstraint Port

Task

<<Abstract>>Resource

GT2Resource <<Abstract>>Dispatcher

GT2Dispatcher

FIGURE 5.15 Class diagram of WFEE.

that are instances of class of Task , Port , and DataConstraint . These objects
are passed on to Workl owModel . Workl owModelToDiGraph converts
Workl ow Model into a directed graph represented by class DiGraph which
encompasses many GraphNode objects. An instance of GraphNode contains
a workl ow task and the references of GraphNodes of its parent and child
tasks. Workl owCoordinator creates and controls the instantiation of
Task M anage r according to the graph node dependencies. Job class repre-
sents a unit of work assigned to a grid resource. Every job has a monitor
implemented by JobMonitor to monitor job execution status on the remote
node. In order to extend WFEE to support multiple grid middleware,
we abstract class Resource and Dispatcher , which provides interfaces that
interact with grid resources.

5.9.2 Event Messages

We have utilized tuple spaces to exchange events. The tuple space model
originated at Yale with the Linda system [13]. A tuple is simply a vector of
typed values (i elds). A tuple space is a collection of tuples that can be
shared by multiple parties by using operations such as read, write, and
delete. In our work, we have leveraged IBM's recent implementation of
tuple spaces called TSpaces [10] to be the event server.
There are three types of event tuples whose format is shown in Table 5.1 ,
task status event , output event , and job status event . The task status event is sent