1. 2003 April 151 Data Centres: Connecting to the Real World Clive Page

2. 2003 April 152 Aim To provide Web Services interfaces to a few data centres to provide realistic data for the current iteration. How data centres many? Maybe three…

3. 2003 April 153 XML Formats for Output ImagesNothing yet Time seriesNothing yet SpectraNothing yet TablesVOTable Conclusion: in this iteration just handle tabular datasets.

4. 2003 April 154 XML Formats for Input AQL (Astronomical Query Language): much discussion, not much progress. ASU (Astronomical Server URL): ad-hoc pre-XML definition of CGI parameters by CDS, used since 1996 by a number of archives. SIAP (Simple Image Access Protocol) – CGI parameters defined by NVO for their prototypes in 2002. Xpath: draft standard for querying XML documents – designed for tree-structured data. Xquery: based on Xpath, includes WHERE section similar to SQL, more suitable for tabular data. SQL: standard for RDBMS but only used by some astronomical archives

5. 2003 April 155 Query Language: proposal for ad-hoc solution Use simplified form of SQL in an XML wrapper: SELECT FROM WHERE includes UCDs so generic queries possible allows same query to be sent to >1 archive may includes column/UCD names and the usual syntax of relational expressions Need special provision for cone-search in selection, e.g. –Boolean pseudo-function CONE(RA, DEC, RADIUS) No joins, no sub-selects, no sorting or grouping, at present.

6. 2003 April 156 Possible Datasets DatasetLocationSystem/DBMSInputOutput APM catalogueCambridgeSolaris/SybaseCGIVOTable 6df galaxy survey EdinburghWin-NT/SQL server?VOTable nearly done USNO-BLeicesterLinux/DB2?XML STP datasetsRALVarious/home grown?VOTable USNO-BLeicester (LEDAS) Solaris/WCStoolsCGIVOtable SuperCOSMOSEdinburghWin-NT/SQL server?VOTable in progress Vizier collection LeicesterLinux/SybaseASUVOTable

7. 2003 April 157 Problem Areas All current services are synchronous: user waits while HTML is generated and streamed to the browser. –How to set up an asynchronous service where results appear later, and are sent to MySpace or elsewhere? How is the query generated in XML format? How is the query in pseudo-SQL parsed into the CGI parameters or SQL the local DBMS needs?

8. 2003 April 158 Metadata Problems How does the query system know which column names exist, or how to translate UCDs to columns? –It gets the information in the Registry How does the Registry get its information on columns and UCDs in each table? Answer: either –It gets the information from the Data Service –OR it gets filled in laboriously by hand. Conclusion Data centres must implement a Web Service which responds to queries about their metadata AQL must be extended to deal with these queries.