The portal is Astrogrid's web-based user interface, a browser being used to interact with services provided by the underlying Astrogrid infrastructure. The purpose being to enable a user to exploit the services and do some astronomy. To a user, the portal is the Virtual Observatory.

The portal itself provides a level of organization that adds value to the raw services. The basic organization centres around seven main pages:

  • Logon. A user must log on before being able to use the VO. There is an email facility to request a userid or the reset of a password if it has been forgotten.
  • Home Page. This is the page displayed after login. It shows the latest jobs submitted by the user, as well as providing access to the client-side desktop applications which are the focus of Astrogrid version 2.
  • MySpace Explorer. Manages the user's virtual file space within the VO.
  • Resource Explorer. Browse the VO registry of available resources.
  • Query Editor. Construct ADQL queries for later submission against some registered data collection.
  • Workflow Editor. Construct and submit for execution workflows which can combine queries and registered astronomical tools in any degree of complexity. A submitted workflow is known as a job.
  • Job Monitor. Review and manage the execution of jobs.

A word is required of the basic ideas behind Astrogrid that have driven organization of the portal.

Astrogrid has been described as a data mining application. There are many collections of astronomical data and the volume of information is expanding at an increasing rate. Unfortunately there is little uniformity here: the collections are both heterogenous and distributed, and large enough to defeat the most ardent researcher. Behind the portal stands the registry, where details of resources are registered in standardized formats suitable for automatic searching by computerised techniques. Astrogrid uses the registry to hold information on both data collections and its own internal resources.

The registry can be explored directly using the Resource Explorer page, but is also of critical importance to the Query Editor and the Worfkflow Editor. The place of query and of workflow in Astrogrid require some explanation...

The aim of the Query Editor is to provide a means of taking information about a data collection from the registry and formating an astronomical query that can be submitted against that data collection. Being able to query against one data collection is an important but in itself limited facility. The results of a query may require further processing or the results of a number of separate queries may need processing and amalgamating in interesting ways. This aspect is fullfilled by workflow, which adds an amount of muscle to the astronomer's toolkit, but also a degree of complexity. The Workflow Editor enables workflows to be designed that can combine queries with the processing of other astronomical tools in a multi-stepped manner. There are no limits other than available processing power and the patience of the astronomer in designing a workflow. Multiple queries can be run, the results analysed, federated and processed by standard tools whose presence has been recorded in the registry. The steps can be processed at different locations. The results of one workflow can be used subsequently as the input of another workflow. Queries, workflows and results can be shared, and thus in important respects become intellectual capital.

It is useful to think of workflows as existing in two contexts. One is design time: workflows must be designed and the designs persist like the blueprint of a building. The other context is execution time. Workflows must be executed to produce results (much like a building must be built using the blueprint). When a user in the Workflow Editor submits a workflow for execution, the workflow becomes known as a job and can be tracked by the Job Monitor page.

A quick reading of the above will show the need for a virtual file system. Query designs, workflow designs and any files used or produced by workflows are held within MySpace, which is the VO's virtual file system. The MySpace Explorer page gives the user access to the user's home space, where all a user's files reside. The physical location of the files is automatically handled by the system, although a certain amount of intervention is allowed if the user so chooses.

Until a full suite of desktop applications becomes available the portal is the user interface into the VO. It is very easy to install with very few prerequisites, although the trick is to get all other components to the state where the portal can begin orchestrating them.