Annotating TAP responses on-the-fly against an IVOA data model

Abstract

With the success and widespread of the IVOA Table Access Protocol (1) for discovering and querying tabular data in astronomy, more than one hundred of TAP services exposing altogether 22 thousands of tables are accessible from the IVOA Registries at the time of writing. Currently the TAP protocol presents table data and metadata via a {TAP\_SCHEMA} describing the served tables with their columns and possible joins between them. We explore here how to add an information layer, so that values within table columns can be gathered and used to populate instances of objects defined in a selected IVOA data model like Photometry, Coords, Measure, Transform or the proposed MANGO container model. This information layer is provided through annotation tags which tell how the columns' values can be interpreted as attributes of instances of that model. Then when a TAP query is processed, our server add-on interprets the ADQL query string and produces on-the-fly, when possible, the TAP response as an annotated VOTable document. The FIELD elements in the table response are mapped to corresponding model elements templated for this service. This has been prototyped in Java, using the VOLLT package library and a template annotation document representing elements from the MANGO data model. This has been exercised on examples based on Vizier and Chandra catalogs.