Development of SAI Catalog Access Services

We present the results of the development of Sternberg Astronomical Institute Catalog Access Services (SAI CAS) project - the first and the only project in Russia, which provides online access to the major astronomical catalogues and different services on top of them. It is developed by a group of astronomers in a framework of SAI Astronet project, funded by Russian Foundation for Basic Research.

SAI CAS is an open-source implementation of the general Catalogue access service (influenced by SDSS CAS & CASjobs project), based on original algorithms and open-source software. We decided to build our own system providing an effective access to the major astronomical catalogues and services, like cross-matching of user data with hosted catalogs. It is important that we pay special attention to the availability of our technology - we use only open-source software with good support and stable history of development - Apache Tomcat, Apache Axis, PostgreSQL and Java language. SAI CAS consists of the database server running PostgreSQL 8.1+, which stores the catalogues and all their metadata, the application server as a set of webservices and pool of JDBC connections to database server, and frontend for interaction with users. Clients could be web browsers or any programs, which communicate with SAI CAS via HTTP and SOAP protocols and can retrieve the data in different formats (VOTable, CSV etc.) The spatial queries and cross-matches in the database are operated using the developed by us Q3C sky indexing scheme and corresponding package for PostgreSQL v.8.1+ which is also freely available. It provides the very fast access to the data with spherical attributes and combines advantages of well-known HTM and HEALPIX indexing schemes.

Currently we provide the ConeSearch service (registered in VO registry) for USNO-A2, USNO-B1, 2MASS point source and extended source catalogues, UCAC-2, and Tycho-2. Other catalogues will be loaded once we obtain them. Access to the ConeSearch service is available from generic web-based interfaces, as well as from programs via SOAP requests. We also have developed the services for easy uploading catalogs to the SAI CAS. We intentionally leave for the future development complex applications like workflow engine, since it's still not clear how to provide astronomers with good interfaces. But the main idea of SAI CAS is to provide the good basis and the good API for building the VO services. SAI CAS already has all the infrastructure to store the catalogues and their metadata and to query them. Thus the building of the Skynode (and any other catalogue-based service) is rather easy and we plan to expose the Skynode web-service within a couple of months.