Assembling the Digital Sky

Continued from page 1

By David Essex

November 22, 2002

The initial NSF-funded work focuses on data interoperability, a key component of which is VOTable 1.0, a data-exchange standard released on April 15 that uses the Extensible Markup Language (XML) to represent large datasets. "We are putting VOTable into practical, everyday use now," Hanisch says. Next on tap: the Simple Image Access Prototype specification, an image-handling complement to VOTable now under discussion with international partners. In addition, Hanisch expects within a year or two to see Web services directories that will make it easier to deliver and search through newly published data.

Metadata (data about data) and Semantic Web technology are two other elements the  NVO team has deemed essential in its ambitious effort to federate the data of an entire scientific discipline. "The rate at which services are being defined is limited by how fast the community can reach consensus on difficult semantic and knowledge-management issues," says Reagan Moore, an associate director at SDSC. "Given the need for a consensus across multiple groups, the services that are being implemented are very impressive." One promising example: researchers at the University of Strasbourg in France created Unified Column Descriptors (UCDs)--standard names for the columns in astronomical tables--that Alex Szalay of Baltimore's Johns Hopkins University, one of the NVO's two principle investigators, has semantically mapped to 1,300 Sloan items.

With so many sites providing content, the NVO will also need a way to indicate how reliable its data is, cautions Michael Skrutskie, principle investigator of the Two Micron Sky Survey and a professor of astronomy at the University of Virginia in Charlottesville. "People will need to know how much trust they can put into those data points." Skrutskie suggests the issue might be solved with a labeling system, and Hanisch says a peer-review process for one is in the works. 

Proponents say the NVO could be up in two to three years, especially if there's money for the operational phase. They plan to demonstrate real-time analysis of clustered galaxies at a January 2003 meeting of the American Astronomical Society in Seattle. The  first showing of interoperability among international VOs should be ready for the July 2003 general assembly of the International Astronomical Union in Sydney, Australia. "I think by the end of two years, we'll have interoperable data centers and a bunch of toolkits," predicts Jim Annis, an astrophysicist at the Fermi National Accelerator Laboratory in Batavia, IL. Longer term, the project could still falter if the NVO's middleware standards make it too expensive for institutions to prepare their survey data, the fault that doomed the pre-Web Astrophysics Data System, in Hanisch's opinion.

Regardless of how it gets assembled, astronomers seem excited about the NVO's potential as a research tool, sometimes referring to it as an instrument on a par with the telescope. "The important part of it is just being able to do searches and queries and being able to get all that information on one object," says Dave Turnshek, a professor in the  astrophysics and astronomy department at the University of Pittsburgh, one of 17 research centers sharing the NSF grant. Turnshek's school paid to get access to the Sloan survey, and he uses it heavily for his research in quasar and galaxy formation. "The exciting thing about the NVO is, eventually everybody will be able to do that," he says.

Adds Hanisch: "My wildest dreams of success are that the VO stuff becomes just part of doing astronomy. It will be just like going to Google."