Unified Access to Astronomy Data via VO-DAS: A Comprehensive Overview of Features and Applications

1. VO-DAS Chenzhou CUI Chao LIU, Haijun TIAN, Yang YANG, etc National Astronomical Observatories, CAS

2. VO Data Access Service (VO-DAS) • An OGSA-DAI based service system to provide unified access to astronomy data, including catalogs, images and spectra. • Goals of VO-DAS • Supporting high volume data query • Interlinking distributed and heterogeneous archives • catalogs, images, spectrums • Providing a software that works for astronomers

3. First Science Paper from China-VO • Candidate Milky Way satellites in the Galactic halo（Liu et al., 2008, A&A) • SDSS DR5 photometric data were searched for new Milky Way companions or substructures in the Galactic halo. • Data analysis procedures were based on the VO-DAS. • Five candidates are identified as over-dense faint stellar sources that have color-magnitude diagrams similar to those of known globular clusters, or dwarf spherical galaxies.

4. Predicted Features • Goals: Uniform access to heterogeneous distributed datasets, bulk of data support • Functions • Catalog, image, and spectrum support • Dataset encapsulating and registry • Data discovery • Metadata description • Jointed query on heterogeneous databases • Bulk of data transfer support • Sync and async queries • Query status tracer • ADQL support

5. Architecture • Components • VO-DASserver • DataNode • Clients • Registry • Data storage

6. Technical Highlights • OGSA-DAIbased data node • Asynchronous query and cross match on distributed databases • Extended ADQL, supporting catalog, image and spectrum at the same time

7. Async Query • Query segmented into sub-queries • Queries assigned to specific DataNodes • Query results transfer among DataNodes • Final results sent to data storage service (VOSpace, FTP, etc) • VO-DAS server supervises the whole process • No data exchange between DataNode and VO-DAS server

8. Extended ADQL • SELECT s.ra, s.dec, s.g-s.i gi, s.i FROM SDSSDR5:star s WHERE s.ra>=120 AND s.ra<=270 AND s.dec>=25 AND s.dec<=70 AND s.i>=19 AND s.i<=22 AND s.g-s.i>=0 AND s.g-s.i<=1 • SELECT f.Access_reference FROM SDSSDR6:specfile f, SDSSDR6:sspParams s WHERE s.specID=f.specID AND f.SNR>10 AND s.alphafea<=0.2 AND s.feha>-0.9

9. VO-DASClients • GUI • CLI • WebBrowser • MATLABClient

10. Interoperability PLASTIC, SAMP

11. VO Tools (Aladin, TOPCAT) PLASTIC Local DB MATLAB Database Toolbox VOTables Java Libraries MATLAB VO-DAS Client VO-DAS MATLAB based DM environments Astrobox

12. AstroBox VO Tools (Aladin, TOPCAT) PLASTIC Local DB MATLAB Database Toolbox VOTables Java Libraries AstroBox MATLAB VO-DAS Client VO-DAS • A plug-in package for MATLAB to provide an astronomical data mining application service, supporting VO protocols and tools. • A high-level data analysis environment supporting: • PLASTIC • VOTable • Local DB • VO-DAS client • Astronomical algorithms

13. MATLAB based DM environments (cont.)

14. Science case：Sub-structure study for the Galaxy

15. Methodology • Density count in area (ra=120~270deg, dec=25~70deg) where i=19~22 and g-i=0~1 in the SDSS DR5 (bin=0.2x0.2deg) • Obtained 524over density area • Calculate CMD for each area • Identify these CMDs by hands

16. Results

17. Work done by VO-DAS • 70 millions records queried from SDSS DR7 database • Calculate CMD for each over density area Other tasks done by MATLAB

18. Lessons learned • Grid and SOAP based data access solution is feasible • Too complex to control • Low performance

19. Current: RESTful TAP DAS

20. Collaboration Environment • CSCW(computer supported cooperative work) • e-Science • VO