Using AstroGrid: an overview

This page gives an overview of some 'typical' steps a user will go through to build a science workflow using AstroGrid, and introduces the AstroGrid portal environments where these tasks can be accomplished.

: Locating resources

A user will want to know which datasets, applications, and other resources are available through AstroGrid. This information is recorded in the AstroGrid Registry, and the most straightforward way to find out what is available is to perform a Registry search. To do this, a user clicks on the Resources icon within the portal, and is taken to the Resources page, where a Registry search can be done by specifying keywords. This allows identification of available datasets and applications, and of the name assigned to them in the AstroGrid Registry. (More on Locating Resources)

: Building a query

Typical usage of AstroGrid will involve quering a specified database for all files meeting a given search requirement. To be processed by the system the query will have to be formulated using a query language: AstroGrid uses ADQL (Astronomical Data Query Language), which is an extension of SQL (Structured Query Language) able to deal with astronomy-specific queries, such as cone searches. To aid in building the query, a query builder is provided. At the end of this process the user saves the query into a file, which will later be sent to the required database using a workflow. (More on Building a query)

: Storing files

Each user has a personal storage space, called MySpace. This storage space is physically distributed on several AstroGrid machines, however this is invisible to the user, to whom MySpace looks like a single storage space. MySpace is where a user typically saves queries and workflows, and collects the results of jobs. Each user account comes with three subdirectories already created: they are called 'queries' (where you store query files), 'workflows'(where you store workflow documents) and 'votable' (where you collect results of jobs, which are in many cases in VOTable format but can also have other formats). Initially it is recommended not to create new subdirectories but work with these existing directories.

In addition to being accessed when one clicks on the MySpace icon, MySpace is also accessed from other AstroGrid pages when the user clicks on 'Save' or 'Load' buttons. This opens a window called the MySpace MicroBrowser. (More on Using MySpace)

: Building a workflow

A user will need to identify all the tasks required for their scientific analysis and specify them in a workflow. In its simplest form, a workflow may involve a series of steps to be done one after the other, for example submit a query to a database (specified in a previously saved query file) and feed the results of the query into an application which operates on the data. More complex workflows may include for example conditional loops, for loops etc.

After constructing a workflow, the user submits it to the system for remote execution. (More on Building a workflow)

: Monitoring job execution

The Job Monitor page allows a user to monitor the progress of jobs submitted and verify when a workflow has completed. From this page, it is possible to access a transcript of the workflow, with details of the execution of each of the workflow 'building blocks'. In case a workflow execution results in 'ERROR', the user can find here details of the problems encountered during execution.

The results of jobs are sent to a user's MySpace, where they can be viewed and/or downloaded to a local machine.

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-- SilviaDalla - 23 Mar 2005