Service infrastructure for cross-matching distributed datasets using OGSA-DAI and TAP

Holliman, Mark

One of the most powerful and important goals for VO developers has been to enable cross-match queries between disparate datasets for end users. This has only been achieved within the VO using the early SkyNode infrastructure and has not been reproduced using current IVOA standards. To remedy that situation, the Wide Field Astronomy Unit (WFAU) has worked with the Edinburgh Parallel Computing Centre (EPCC) in leveraging the OGSA-DAI grid middleware to enable cross catalogue queries on distributed VO services. We have achieved this goal by building a three layer service stack that places the OGSA-DAI software above multiple individual services implementing the IVOA’s new Table Access Protocol (TAP), and then a single TAP service is placed above this and presented to the end users. Users can then execute ADQL queries that cross-match between the disparate datasets as though they were in the same database with acceptable performance rates on the resulting data flow.

The OGSA-DAI software is able to interrogate any compliant TAP service to acquire the necessary metadata for insertion into the single federated TAP service used for cross-match queries. We are currently testing this distributed infrastructure using the TAP services provided by WFAU for the UKIDSS DR4 and SDSS DR7 datasets in combination with the TAP service available from the Canadian Astronomy Data Centre (this last without requiring any action from CADC staff). This forms the basis for a large-scale distributed data mining workflow and similar activities can be readily implemented as more TAP services come online. Future work will involve releasing this infrastructure to the greater astronomical community as an IVOA compliant service for users.

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