Contents

Overview

A workflow aims to accomplish a complex piece of work. In Astrogrid terms this would be an astronomical investigation. If the work could be done in one simple step (eg: by executing a single program from the command line), then it would hardly be a workflow. A prime dimension of a workflow is therefore that the objective will take more than one step to accomplish - it has a degree of complexity.

A simple example of a workflow might consist of the following steps:

  1. Make a query against against one catalog (say a cone search of one area of the sky).
  2. Make a similar query against another catalog.
  3. Merge the contents.
  4. Analyse the resulting data.
Each step is usually the invocation of a separate computer program (a task), each task requiring its own inputs and outputs. Some inputs to a step will be astronomical data, and some inputs will be control information for the selected tool. Outputs will normally be processed data destined as a final result, or as intermediate data to be used as inputs for subsequent steps within the workflow.

For Astrogrid, the final result of executing a workflow is usually a file held in MySpace. From that viewpoint, Astrogrid workflow is itself an intermediate tool, since we would envisage the final results file being subsequently loaded into another tool, for example, for visualization, or even for input into a different workflow.

Astrogrid tries to deal with the complexity of workflows. But it is not an easy thing to eliminate. We hold workflow designs as XML documents. This is a particularly verbose way of describing an individual workflow, but is convenient for its rigour. There is no necessity to interact directly with a workflow xml document and therefore there is no necessity to be intimately equainted with it; the portal workflow builder page hides most of the intricacies.



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Workflow

As mentioned workflow documents can be very complex but the browser tries to hide as much of the complexity as possible. Initially you may find running some of the Parameterized workflows and viewing the resulting workflow via the Job Monitor page a good introduction.

On entering the workflow builder page for the first an empty workflow document is created; this consists of a workflow containing a single sequence. You can add a name and description to your workflow to identify it at a later time (once a workflow is submitted to the Job Entry System it will also be given a unique Job ID).

To start building your workflow move the mouse over the sequence to highlight it, then from the 'edit' menu select the activity to add to the sequence (in this case a step). Select wether you wish to add the activity before/here/after the item you have highlighted (if you are inserting an activity into the initial sequnce then it is only possible to insert 'here').

When you insert an activity your workflow will be re-drawn to display the change.

As you move your mouse over each activity details about it are displayed at the bottom of the screen. Note that each activity displayed contains a help button with information on how it will work.

As mentioned each step will contain a task. To select a particular task highlight the step you are interested in, and either select a task from selection presented in the drop-down list or select browse the registry (as the registry may contain many 100's of tasks the drop-down list contains only a small selection). If you choose to search the registry for a task a new window will open allowing you to do detailed registry searches.

Once you have selected a task, and optionally added other information to your step, press update step details.

Each task will require a number of parameters - right clicking a step that contains a task will display details of the required parameters, and allow you to enter your chosen values.

Certain parameters will accept indirect references as their value e.g. a task may require a file as an input, or produce a file as an output. Pressing the browse key will open a MySpace browser window so that a particular file located in your MySpace may be selected.



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File

The File menu contains 4 options:

  • New: create a new workflow.
  • Open: open a workflow that has been previously saved to your MySpace. A sepererate MySpace browser window will open.
  • Save: save your current workflow into your MySpace. A sepererate MySpace browser window will open.
  • Submit: submits your current workflow to the Job Entry System, it's status can then be viewed in the Job Monitor pages.



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Edit

Once you have highlighted an activity you can select which activity to add and it's position (before/here/after):

  • step - contains a task
  • flow - composes a set of activities into a parallel structure - the activities in the flow will be executed simultaneously.
  • sequence - composes a set of activities into a linear structure - they will be executed sequentially in order.
  • logic - if/else, scope, script, set, unset
  • loop - for loop, while loop
  • etc...



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