08.02.2013 Views

New Statistical Algorithms for the Analysis of Mass - FU Berlin, FB MI ...

New Statistical Algorithms for the Analysis of Mass - FU Berlin, FB MI ...

New Statistical Algorithms for the Analysis of Mass - FU Berlin, FB MI ...

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

142 CHAPTER 5. COMPUTER SCIENCE GRID STRATEGIES<br />

Figure 5.6.10: An example workflow shown on <strong>the</strong> left. On <strong>the</strong> right hand side <strong>the</strong><br />

parameters <strong>of</strong> <strong>the</strong> selected icon (highlight in yellow) are shown. The gray and purple<br />

bars at <strong>the</strong> top are <strong>the</strong> toolbars containing <strong>the</strong> available workflow components.<br />

create large pipelines to solve complex problems, e.g. a combination <strong>of</strong> many<br />

preprocessing steps followed by a multi-level analysis <strong>of</strong> data. A big advantage<br />

<strong>of</strong> workflows over manual execution <strong>of</strong> different tools is that a workflow is<br />

designed once and <strong>the</strong>n applied to many different datasets (even in parallel).<br />

For a workflow system we need two basic components: (a) <strong>the</strong> workflow<br />

designer and (b) a workflow execution module, which are described below. In<br />

<strong>the</strong> QAD Grid system each workflow component is ei<strong>the</strong>r (1) a QAD Grid<br />

service which will be handled by a worker (e.g a particular analyses), (2)<br />

a basic programming language function (such as an if/<strong>the</strong>n condition or a<br />

variable assignment) or (3) an extended workflow function (such as sending<br />

an email or deleting a file).<br />

In <strong>the</strong> QAD grid system workflows are modeled as rooted directed graphs.<br />

Since we allow (conditional) jumps (see below) it can contain cycles. Figure<br />

5.6.10 shows a small section <strong>of</strong> an example workflow. The left hand side <strong>of</strong><br />

<strong>the</strong> figure shows <strong>the</strong> workflow in <strong>the</strong> workflow editor. Each icon represents<br />

one component <strong>of</strong> <strong>the</strong> workflow. At <strong>the</strong> right hand side, <strong>the</strong> parameters <strong>of</strong><br />

<strong>the</strong> selected item (dyed in yellow) are shown: since this component is a “send<br />

email” item one needs to specify <strong>the</strong> receiver address and a mail body. O<strong>the</strong>r<br />

items would presumably have more parameters.<br />

An important concept in <strong>the</strong> QAD Grid workflow system is <strong>the</strong> usage <strong>of</strong><br />

user defined variables. These variables allow <strong>the</strong> assignment <strong>of</strong> values to workflow<br />

variables at execution time. That means, a workflow can be designed and<br />

variables, such as <strong>the</strong> dataset to be analyzed or particular algorithm parameters,<br />

can be set by <strong>the</strong> user when <strong>the</strong> workflow is executed.<br />

5.6.1 Workflow Elements<br />

The following paragraphs describe <strong>the</strong> elements that can be used to build a<br />

workflow.

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!