Astronomical Data Query Language Simple Query Protocol for the Virtual Observatory Naoki Yasuda 1, William O'Mullane 2, Tamas Budavari 2, Vivek Haridas 2, Martin Hill 3, Nolan Li 2, Tony Linde 3, Tanu Malik 2, Bob Mann 3, Yoshihiko Mizumoto 1, Masatoshi Ohishi 1, Clive Page 3, Alex Szalay 2 1 National Astronomical Observatory of Japan 2 Johns Hopkins University, USA 3 AstroGrid, UK The mission of IVOA is to facilitate the international coordination and collaboration necessary for the development and deployment of the tools, systems and organizational structures necessary to enable the international utilization of astronomical archives as an integrated and interoperating virtual observatory. VOQL is currently under discussion in the IVOA forum. See Current thinking is – VOQL has 3 layers as depicted below. ADQL and SkyNode constitute layer 1. Select t.*, b.* From Tab t, Bob b Where t.g <> b.g and Region('Circle J ') The Astronomical Data Query Language (ADQL) is a proposed standard query language for the interoperability of the International Virtual Observatory. The data servers in the International Virtual Observatory could be searched using an ADQL query. The servers would return as a minimum VOTables as a result of the query (other formats may be supported by some nodes). t b Tab t Bob b t g <> b g Ra Dec Converter between ADQL and SkyQL : SkyQL is a string like representation of ADQL. Semantically SkyQL and ADQL are identical. Syntactically ADQL is XML and SkyQL is more human readable. ADQL is passed as an XML document to the Query Interface. ADQL is based on a subset of SQL plus Region and XMatch. The only SQL command allowed in ADQL is a “select”. All data servers joining the International Virtual Observatory would implement a standard IVOA SkyNode Interface based on SOAP (Simple Object Access Protocol) Web Services. See current proposal specification on ADQL, SkyQL, and SkyNode The main element of ADQL - SELECT The following is an example of simple SkyQL and its ADQL (XML) representation. A converter exists to exchange these formats (url listed below). Further tools and information may be found at The Virtual Observatory Query Language Table part of the select statementWhere part of the select statement Query in SkyQL Query in ADQL Cross matching between tables will be supported in Full SkyNode (higher level SkyNode). The service XMatch() takes an ADQL structure and a set of VOTables. An example of the SkyQL (which would be expressed in ADQL format) is select.... from SDSS:PhotoObj o, EXT:0 my1, EXT:1 my2 where XMatch(o,my1,my2) < 3 Virtual Observatory Portal will be constructed on top of SkyNode’s services to federate multiple data servers. One example of such portal is Open SkyQuery Portal which is open version (not restricted on Microsoft Technology) of SkyQuery ( See details on poster by Budavari. The diagrams with pale yellow background are part of Schema diagrams for ADQL. These may be helpful to understand the ADQL structure. See the XSD ( for complete structure of ADQL. The XML document in the center of the poster is a valid ADQL document with relevant parts linked to the schema diagrams to aid understanding. From this document it is clear why we might like a human readable SkyQL (top of poster) as well as the machine readable ADQL. XMATCHXMATCH SkyNode Interface These are the Pseudo methods for the SkyNode Interface. BASIC SkyNode //Return RSM compliant VOResource public VOResource MetaData(); //Return a list of all tables that may be used from this node. public string[] Tables(); //Return ucd, name, unit, type for each column of table public MetaColumn[] Columns(); //Return available query result formats public string[] Formats(); //Return the result of executing ADQL query in requested format public VOResult PerformQuery(Select query, string format); FULL SkyNode // Return result of executing an ExecPlan, format specified in plan public VOResult ExecutePlan(ExecPlan plan); //Return region of intersection between given region and this SkyNode public Region Footprint(Region region); //Returns object density per square degree for a given criteria. public float PerformanceQuery(Select query); //Return Cross matched objects according to Query and input Tables") public VOResult XMatch(Select select, VOTABLE[] votables); SkyNode The services of IVOA SkyNode is defined as WSDL (Web Services Definition Language) at WSDL definition enables automatic code generation of Web Services e.g. using Microsoft.NET or Apache Axis. Brief overview of the interface is given below.