P1254325790yehat

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Astronomical Data Query LanguageSimple Query
Protocol for the Virtual Observatory
Naoki Yasuda1, William O'Mullane2, Tamas
Budavari2, Vivek Haridas2, Martin Hill3, Nolan
Li2, Tony Linde3, Tanu Malik2 , Bob Mann3,
Yoshihiko Mizumoto1, Masatoshi Ohishi1, Clive
Page3, Alex Szalay2 1 National Astronomical
Observatory of Japan 2 Johns Hopkins University,
USA 3 AstroGrid, UK

The Virtual Observatory Query Language
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
http//skyservice.pha.jhu.edu/develop/vo/adql/.
VOQL is currently under discussion in the IVOA
forum. See http//www.ivoa.net/twiki/bin/view/IVOA
/IvoaVOQL. Current thinking is VOQL has 3
layers as depicted below. ADQL and SkyNode
constitute layer 1.
Query in SkyQL
Select t., b. From Tab t, Bob b Where t.g ltgt
b.g and Region('Circle J2000 12.5 23.0
5.')
ADQL, SkyQL, and SkyNode
Converter between ADQL and SkyQL
http//skyservice.pha.jhu.edu/devel/AdqlTranslat
or/Convertor.aspx http//skyservice.pha.jhu.edu/de
vel/AdqlTranslator/AdqlToSql.aspx
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).
Query in ADQL
lt?xml version"1.0" encoding"utf-16"?gt ltSelect
xmlnsxsd"http//www.w3.org/2001/XMLSchema"
xmlnsxsi"http//www.w3.org/2001/XMLSchema-instan
ce"gt ltSelectiongt ltExprSelectionItemgt ltColumn
Exprgt ltAllColumnReferencegt ltTableNamegttlt/
TableNamegt lt/AllColumnReferencegt lt/ColumnEx
prgt lt/ExprSelectionItemgt ltExprSelectionItemgt
ltColumnExprgt ltAllColumnReferencegt ltTabl
eNamegtblt/TableNamegt lt/AllColumnReferencegt lt
/ColumnExprgt lt/ExprSelectionItemgt lt/Selectiongt
ltTableClausegt ltFromClausegt ltTableReferencegt
ltTablegt ltNamegtTablt/Namegt ltAliasNamegt
tlt/AliasNamegt lt/Tablegt ltTablegt ltNamegt
Boblt/Namegt ltAliasNamegtblt/AliasNamegt lt/Tab
legt lt/TableReferencegt lt/FromClausegt ltWhereC
lausegt ltIntersectionSearchgt ltFirstCondition
xsitype"PredicateSearch"gt ltComparisonPredgt
ltFirstExpr xsitype"ColumnExpr"gt ltS
ingleColumnReferencegt ltTableNamegttlt/TableN
amegt ltNamegtglt/Namegt lt/SingleColumnR
eferencegt lt/FirstExprgt ltComparegtltg
tlt/Comparegt ltSecondExpr xsitype"ColumnExp
r"gt ltSingleColumnReferencegt ltTableN
amegtblt/TableNamegt ltNamegtglt/Namegt lt/
SingleColumnReferencegt lt/SecondExprgt lt/
ComparisonPredgt lt/FirstConditiongt ltSecondC
ondition xsitype"RegionSearch"gt ltCircle
xmlnsq1"urnnvo-region" xsitype"q1circleType"
gt ltq1Centergt ltPos2Vector
xmlns"urnnvo-coords"gt ltNamegtRa
Declt/Namegt ltCoordValuegt ltValuegt
ltdoublegt12.5lt/doublegt ltdoublegt2
3lt/doublegt lt/Valuegt lt/CoordValuegt
lt/Pos2Vectorgt lt/q1Centergt ltq1
Radiusgt5lt/q1Radiusgt lt/Circlegt lt/SecondC
onditiongt lt/IntersectionSearchgt lt/WhereClause
gt lt/TableClausegt lt/Selectgt
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.
SkyQL is a string like representation of ADQL.
Semantically SkyQL and ADQL are identical.
Syntactically ADQL is XML and SkyQL is more human
readable.
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 http//www.ivoa.net/inte
rnal/IVOA/IvoaVOQL/SkyNodeInterface-0.5.doc
The main element of ADQL - SELECT
SkyNode The services of IVOA SkyNode is defined
as WSDL (Web Services Definition Language) at
http//skyservice.pha.jhu.edu/devel/SkyNode/SkyNod
e.asmx?wsdl. 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.
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)
Table part of the select statement
Where part of the select statement
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 SDSSPhotoObj o, EXT0 my1, EXT1
my2 where XMatch(o,my1,my2) lt 3
X M A T C H
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
(http//skyservice.pha.jhu.edu/devel/AdqlTranslato
r/ADQLschema.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.
Virtual Observatory Portal will be constructed on
top of SkyNodes 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
(http//www.skyquery.net). See details on poster
by Budavari.
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.