This week, I have been attending the semi-annual IVOA meeting in Urban-Champaign, Illinois. One of the most interesting series of talks was on how three new observational projects in their commissioning phase are using Virtual Observatory (VO) services as part of their data management and data dissemination plans. These projects are the Dark Energy Survey (DES) (presented by Don Petraveck), the One-Degree Imager (ODI) (presented by Arvin Gopu) and the Atacama Large Millimeter Array (ALMA) (presented by Felix Stoehr).
If you are not familiar with the VO, the term refers to a collection of projects funded usually at the national level that cooperates with other VO projects to enable uniform access to astronomy data housed worldwide. These projects work together as members of the International Virtual Observatory Alliance (IVOA) to meet this goal. The U.S. VO project, the Virtual Astronomical Observatory (VAO) is an active participant in the IVOA. The scientific goal of the VO is to use a uniform set of queries enable astronomers to discover data sets worldwide and aggregate them into new data products and to perform new scientific analyses. The VO does this by developing standards and protocols to support common queries to disparate and inhomogenous data sets distributed across the globe, and by developing innovative ways of efficiently querying very large data sets.
All three projects mentioned above will generate large volumes of data that will eventually be made accessible to the public. The Dark Energy Survey will use a custom built camera to probe why the expansion of the universe is accelerating. The One Degree Imager will be a facility instrument available to the astronomical community that will capture one-square degree images of the sky, and Atacama Large Millimeter Array is an array of radio telescopes under construction in Chile.
All three projects need to build data systems on a limited budget, and are therefore trying to build them as much as possible out of existing components, especially those that can be plugged together as modules.
DES has designed a simple data system plans to manage the data from the camera. They plan to plug-in, on top of this system, two VO protocols to provide access to images (Simple Access Image Protocol, SIAP) and to tables of source catalogs, their primary data products (Table Access Protocol, TAP).
ODI already uses VOTable, the VO standard for transferring tabular data, encoded as XML, into the Pipeline, Portal and Archive (PPA) data system. The project plans incremental updates to the PPA, including SIAP, TAP and an image cutout service. An interesting aspect of the PPA is that it is also designed to incorporate users’ custom workflows.
ALMA plans to advantage of the next generation image protocol, SIAP, to serve image cubes, their primary data products. And they plan to use ObsTAP, the table access protocol backed with a data model, to serve catalog data via an OpenCADC library. Finally, they plan to use WebSAMP to plug together on-line tools. Future tools include image cutout services, using VOSpace, an interface to distributed persistent storage, and managing job execution with Universal Worker Services (UWS).
The ALMA speaker, Felix Stoehr, made these recommendations to the IVOA:
- Keep it simple!
- Standards should not evolve (or they are not standards); if they do change, they should be backwards compatible.
- Less is more – keep the number of standards small.
- Make sure that searches go beyond positional attributes.
Felix cited ObsTAP as an example of a general purpose protocol, with its four physical axes and mandatory keywords.