vo query language gsfc xml group ed shaya brian thomas kirk borne
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VO Query Language
GSFC XML Group
Ed Shaya
Brian Thomas
Kirk Borne
May 12-16 2003 IVO Meeting @ Cambridge
VOQL Requirements
Provide a means for users to submit general requests for astronomical information from a distributed set of repositories.
Allow for the science use cases. Easy to learn and use:
– Hide from the user obvious but tedious steps– May require several levels o f language with only the top level being
easy. Allow for web form entry. Independent of internal arrangement of data at repositories. Plug-n-play metadata and ontology. Span a distributed set of heterogeneous services.
– Each VO query can transform to multiple queries in local dialects.– Workflow of interactions between registries, services, and user.– Integration of multiple responses
May 12-16 2003 IVO Meeting @ Cambridge
More VOQL Requirements
Easy to parse and transform into other forms Extensible
– Sites can extend query language through local namespaces– VO namespace can add language elements into the future.
May 12-16 2003 IVO Meeting @ Cambridge
XML Query Language
Compatible XML and Human-Readable versions Xquery is a superset of Xpath Based on Quilt, XQL, and XML-QL
– Quilt is based on Object Query Langauge (OQL)– OQL is based on Structured Query Language (SQL)
If,then,else: case switch: basic functions: define new functions FLWR (for, let, where, return)
for $i in (1 to 3)
let $j := (1 to $i)
Results in:
$i = 1, $j = 1
$I = 2, $j = (1,2)
$I =3, $j = (1,2,3)
May 12-16 2003 IVO Meeting @ Cambridge
XQuery Continued
for $s in document('‘bright_stars.xml'')/*/id_mainlet $b := document('‘photometry.xml'')/*/star[name =
$s]/band where count ($b) > 1
return<colors>
<starName>$i</starname>for $j in (2 to count($b))<color name=“$b[$j]@name - $b[$j-
1]@name”>$b[$j]/value - $b[$j-1]/value
</color></colors>
May 12-16 2003 IVO Meeting @ Cambridge
May 12-16 2003 IVO Meeting @ Cambridge
OLAP/XMLA
On-line Analytical Processes Reduces bandwidth/time of data out Statistical Package add on to Databases Analysis of DataCubes
– Hierarchy of Axis Values Years, Months, Days, Hours, minutes Degrees, minutes, seconds Interior, core, mantle, atmosphere, mesosphere, exosphere
May 12-16 2003 IVO Meeting @ Cambridge
JVO Query Language – Naoki Yasuda
Retrieves catalog data and images from multiple data servers via a single user interface
Extension of SQL– Catalog.UCD– Box(Point(c1.ra,c1.dec), width1,height1)– XMATCH(c1,c2,!c3,…)< 3 arcsec– Select Catalog: Keyword1 & Keyword2
Select by [[MAX|MIN](PROPERTY) | ALL] [NAME]
– Area : [inside|outside] area0
Area1 [overlap|union] area2 | shape
SHAPE: box, circle, oval, triangle,point
DIFF(x.obs_date, y.obs_date) > 30 days
May 12-16 2003 IVO Meeting @ Cambridge
Data mining
Beyond finding data; intense data filtering, conditioning, knowledge synthesis.
Grid Services?– Principal Component Analysis– Iterative solutions– Genetic algorithms– Maximum-likelihood functions– Neural nets– Decision trees – Cluster analysis– Regression analysis
May 12-16 2003 IVO Meeting @ Cambridge
Data Objects
Dataset– Tables
Fields– Units– Class (UCD)– Range– Values
– Images Axes Coordinate Maps Data Values
– Spectra Wavelength Intensity
May 12-16 2003 IVO Meeting @ Cambridge
ADQL
Obtain Data Sets– By bibliographic query
Author, date published, title, journal, volume– By description
Keywords, abstract, mission name Obtain tables
– By title, table #, field names – By Xpath
/LocalGroup/[galaxy=“M31”]/region7/v-band– Obtain table data by UCDs or field names– Min/max of range, regular expression
Obtain N-cube data– Subset by axis values, – subset by ra,dec, radius or more generally Func(axes1..)
May 12-16 2003 IVO Meeting @ Cambridge
Astronomy Data Query Language (ADQL)
May 12-16 2003 IVO Meeting @ Cambridge
ADQL/Query Schema
May 12-16 2003 IVO Meeting @ Cambridge
Knowledge Based Query
Class Instance Objects Property (V-band) Instance value (-1.4)
– Measurement property values are Data – Modifier (aperture) Instance value (3 arcsec)
Modifier (inequality) Instance value (before, not)
– Aggregate property – member, region, component Values are bags of objects
– SubclassOf property – subclass has restricted property value range or restricted list of properties.
Property Space – N-properties form a space. A bit of math is needed to relate values.
May 12-16 2003 IVO Meeting @ Cambridge
Problem Statement Language: Root
May 12-16 2003 IVO Meeting @ Cambridge
PSL Constraint
May 12-16 2003 IVO Meeting @ Cambridge
PSL AstroObject
May 12-16 2003 IVO Meeting @ Cambridge
<dataset subject="astronomy">
<title>AC 2000.2: The Astrographic Catalogue on the Hipparcos System</title>
<altname type="ADC">1275</altname>
<altname type="CDS">I/275</altname>
<altname type="brief">The AC 2000.2 Catalogue</altname>
<references type="source">
<reference>
<title>AC 2000.2: The Astrographic Catalogue on the Hipparcos System</title>
<author><initial>S</initial><initial>E</initial><lastName>Urban</lastName></author>
<author><initial>T</initial><initial>E</initial><lastName>Corbin</lastName></author>
<author><initial>G</initial><initial>L</initial><lastName>Wycoff</lastName></author>
<author><initial>E</initial><lastName>Hoeg</lastName></author>
<author><initial>C</initial><lastName>Fabricius</lastName></author>
<author><initial>V</initial><initial>V</initial><lastName>Makarov</lastName></author>
<journal><name>Astron. J.</name><volume>115</volume><pageno>1212</pageno>
<date><year>1998</year></date><bibcode>1998AJ....115.1212U</bibcode>
</journal>
</reference>
</references>
Dataset Schema
May 12-16 2003 IVO Meeting @ Cambridge
<keywords
xml:base=http://adc.gsfc.nasa.gov/keywordLists/adc/ parentListURL="adc_keywordList.html">
<keyword xlink:href="kw_p.html#Positional_data">Positional data</keyword>
<keyword xlink:href="kw_a.html#Astrographic_zones">Astrographic zones</keyword>
<keyword xlink:href="kw_s.html#Surveys">Surveys</keyword>
</keywords>
<descriptions>
<description>
<para>
The AC 2000.2 is a revised version of the 1997 release of the AC 2000 (Cat. <I/247>). It was decided that the availability of an improved reference catalogue and the inclusion of photometry from the Tycho-2 catalogue would be sufficient to warrant a complete re-reduction of the data and a new distribution of the catalogue. The AC 2000.2 catalog contains positions of 4,621,751 stars at the average epoch of plate exposures for each star (average 1907).
</para>
</description>
Dataset Continued
May 12-16 2003 IVO Meeting @ Cambridge
Case Study 0: Setting up the Query
Return RA, Dec, Vmag for stars with 13<Vmag<15 and 10:12:53.5<RA<13:13:43 and 18:38:00<DE< 18:40:00.
PSL: <object class=“star”>
<property name=“Vmag”><range min=“13” max=“15”/><value>?vmag</value>
</property><property name=“RA”>
<range min=“10:12:53.5” max=“13:13:43”/>\<value>?ra</value>
</property><property name=“DE”>
<range min=“18:38:00” max=“18:40:00”/><value>?de</value>
</property></object>
May 12-16 2003 IVO Meeting @ Cambridge
Case Study 0: Mapping Query to Metadata
Search for tables with metadata that satisfy: – Object/[class=“star”] –search-> keyword, description– Property[@name=“Vmag”] –search-> field/UCD, name– Property[@name=“RA”] –search-> field/UCD, name– Property[@name=“DE”] –search-> field/UCD, name– Property/range –search-> field/min and field/max or coverage
attributes
For all such tables, return: ?vmag, ?ra, ?de Also, return group/field[@name=“error”] for group with
Vmag info.
May 12-16 2003 IVO Meeting @ Cambridge
Problem Statement Language (PSL)
Begin RequestConstraint
Find astronomical objects with the following properties: AND these properties 1. Name: assign to var1 2. Class is "cluster of galaxies | galaxy cluster" 3. Measurement quantities satisfy: a. X-ray brightness > 3.3E7Jy : assign to var2 1. Time interval of measurement: 1998Y-1999Y
Using the above variables satisfy, the math formulae:
1. (var2 + var3) < (var1 – log[var4]) OR these constraints [several constraints for which one must be true etc ]Return a table with the following sequence of fields: var1 var2
End Request
PSL Pull down
AndConstrainties, Andproperties
PSL Pull down
AndConstrainties, Andproperties
Property Name Pull Down
Name, Class, etc.
Property Name Pull Down
Name, Class, etc.
MathML Pull down
*,-,/,+,sum,avg,<,>, etc
MathML Pull down
*,-,/,+,sum,avg,<,>, etc
May 12-16 2003 IVO Meeting @ Cambridge
Brian Thomas’ Infrastructure
May 12-16 2003 IVO Meeting @ Cambridge
Tony Linde’s Infrastructure
VO activity – User – Problem Assistant – service to help user state the problem– Ontology – terms and relationships derived from existing data
Workflow – to retrieve data, merge it, analyze it, reduce it Registry – lists all services and their high level metadata Job Control – decides which jobs and when Data Centre – receiver of query for all internal data sources Data Source Service – uses translator to restate query Translator – from data query language to implemented service Languages
– Problem Statement Language (PSL) – Workflow Language (WFL) – Astronomical dataset Query Language (ADQL) – Ontology Query Language (OQL) – Registry Query Language (RQL)
May 12-16 2003 IVO Meeting @ Cambridge
Conclusion
Metadata should clearly distinguish between values that are property values and those that are modifiers of properties.
Then, a mapping from a natural(ish) scientific knowledge based language (PSL) to a request language for data-center common items (ADQL) is possible.
A federated system with a VO-wide vocabulary plus specialized (local) namespaces is best for getting started right away and permitting for evolution.
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