jvo query language
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IVOA Interoperalibity 2003 1
JVO Query Language
Naoki Yasuda (NAOJ/Japanese VO)
IVOA Interoperalibity 2003 2
Basic Functions of JVOQL
• Query and retrieve required data– Describe query condition– Describe what to retrieve– Describe analyses on retrieved data
• Federate distributed databases– Describe queries for multi databases in one unit
• Federate catalogs (tables) and images– Need not to discriminate catalogs and images
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Requirement for JVOQL
• Platform independent– VO will be constructed as heterogeneous
system– Query must be transferable among systems
• Sufficient to describe astronomical queries– QL must describe what astronomers want to do
• Easy to understand for human and machine– Necessary for debugging and programming
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Format of JVOQL
• JVOQL adopted SQL as a base language– SQL is a well-defined query language optimized for
relational database– SQL is easy to understand for human and machine– Backend queries can be done by DBMS
• Astronomy specific functions are defined as extensions for SQL– SQL is not sufficient enough for astronomical queries
• XMATCH (Cross Matching)• AREA (Image cutout / Celestial area limit)
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Extension 1 : Cross-Matching
• Astronomical objects will be identified mainly based on its celestial position (and distance from the earth).
• Distributed databases can be related through celestial positions.
• Similar to ‘join’ in SQL– where A.id = B.id
– where XMATCH(A, B) < 3 arcsec
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XMATCH
• XMATCH(A, B, !C, …) < 3 arcsec– Select objects whose celestial positions in catal
og A and catalog B coincide within the tolerance of 3 arcsec but not found in catalog C.
Catalog A Catalog B Catalog C
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Extension 2 : Image cutout
• In most cases, astronomers request images associated with objects selected from catalogs.– Cutout area will be defined as celestial area.
• Celestial area definition can be used to limit searching celestial area.
• Image cutout can be easily expressed like SQL– select A.ra, A.dec, A.BOX(POINT(A.ra, A.dec, J2000), 3 arcmin, 3 arcmin)
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AREA
• POINT(long, lat, coord) will define a point on the celestial sphere.– coord could be J2000, B1950, GAL, …
• AREA will be defined based on POINT– BOX(POINT(…), width, height[, PA])CIRCLE(POINT(…), radius)OVAL(POINT(…), rad1, rad2[, PA])TRIANGLE(POINT(…), POINT(…), POINT(…))
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Sample Querycreate view myEROtable asselect s.ra, s.dec, s.Rmag, t.Kmag, sr.BOX(POINT(s.ra, s.dec, J2000), 1 arcmin, 1 arcmin) as Rimage, tk.BOX(POINT(s.ra, s.dec, J2000), 1 arcmin, 1 arcmin) as Kimagefrom SUBARU s, 2MASS t, SUBARU.R sr, 2MASS.K tkwhere XMATCH(s,t) < 3 arcsec and (s.Rmag-t.Kmag) > 6 mag and BOX(POINT(201.0 deg, 27.4 deg, J2000), 1 deg, 1 deg)
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Sample Querycreate view myEROtable asselect s.ra, s.dec, s.Rmag, t.Kmag, sr.BOX(POINT(s.ra, s.dec, J2000), 1 arcmin, 1 arcmin) as Rimage, tk.BOX(POINT(s.ra, s.dec, J2000), 1 arcmin, 1 arcmin) as Kimagefrom SUBARU s, 2MASS t, SUBARU.R sr, 2MASS.K tkwhere XMATCH(s,t) < 3 arcsec and (s.Rmag-t.Kmag) > 6 mag and BOX(POINT(201.0 deg, 27.4 deg, J2000), 1 deg, 1 deg)
common constraint
multiple DB constraints
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select count(*)from SUBARU swhere BOX(POINT(201.0, 27.4, J2000), 1.0, 1.0)
select count(*)from 2MASS tWhere BOX(POINT(201.0, 27.4, J2000), 1.0, 1.0)
count 1
count 2
First count the number of objects which satisfies common constraints
According to the counts, server access sequence will determined
count 1 count 2>
2MASS
SUBARU
count 1 count 2<
2MASS
SUBARU
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select s.ra, s.dec, s.Rmagfrom SUBARU swhere BOX(POINT(201.0, 27.4, J2000), 1.0, 1.0)
select t.Kmagfrom 2MASS twhere XMATCH(s,t) < 3 arcsec and (s.Rmag-t.Kmag) > 6 mag
select sr.BOX(POINT(s.ra, s.dec, J2000),…) as Rimagefrom SUBARU.R sr
select tk.BOX(POINT(s.ra, s.dec, J2000),…) as Kimagefrom 2MASS.K tk
Output Table A
Output Table B
Output Table C
Result Table
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Extension of AREA
• Usual queries are for catalogs• There is a need for query for area like
– Search for area where V band, I band, and K band observations are available.
– Search for area where observed in B band more than 3 times and their intervals are more than 1 month.
– …
• These queries will expand the usefulness of astronomical data archives.
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Sample Queries
select s.a, t.a, ...from SUBARU.R s, 2MASS.K t, ...where (s.AREA() OVERLAP t.AREA()) as a
select x.a, y.afrom SUBARU.B x, SUBARU.B ywhere (DIFF(x.obs_date, Y.obs_date) > 30 days) and (s.AREA() OVERLAP t.AREA())) as a
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s.AREA() t.AREA()
AREA info
OVERLAP
cutout request
Div
ide
into
pi
eces
s ta1a2a3
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