VOTable 1'1

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VOTable 1.1

• Raúl Gutiérrez Sánchez
• SVO, LAEFF-INTA
• raul_at_laeff.esa.es

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VOTable

• XML format for the interchange and storage of
  tabular data in the VO framework.
• Composed by
• Metadata description of the data and its
  structure.
• Data local or remote.

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XML

• XML is a cross-platform, software and hardware
  independent tool for transmitting information.
• Can be used to
• Share data just plain text, so no
  incompatibility.
• Store data in files or databases.

Ideal for the VO!
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XML (main characteristics)

• XML was designed to carry data XML was designed
  to describe data and to focus on what data is.
• XML does not DO anything XML was created to
  structure, store and to interchange information.
  Someone must write a piece of software able to
  deal with it.
• XML is free and extensible XML tags are not
  predefined, you must invent your own tags.

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XML Syntax (example)
lt?xml version1.0 encodingISO-8859-1?gt ltnotegt
lttogtPatricialt/togt ltfromgtAlexlt/fromgt
ltheadinggtBuy Beerlt/headinggt ltbodygtDont forget
to buy beerlt/bodygt lt/notegt
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XML Syntax

• All XML elements MUST have a closing tag.
• XML tags are case sensitive. ltNotegtThis is
  incorrectlt/notegt
• XML elements must be properly nested.
  ltbgtltigtincorrectlt/bgtlt/igt
• All XML elements MUST have an unique root
  element.
• Attribute values must always be quoted (single or
  double).
• With XML, white space is preserved
• CR/LF is converted to LF.
• Comments lt!-- This is a comment --gt

Nothing special, just plain text with some tags
enclosed in angle brackets.
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XML - VOTable

• Well formed XML doc. ? Valid XML doc.
• Well formed conform to the XML syntax.
• Valid also conform to an XML Schema (or DTD)
• XML Schema define the legal building blocks and
  the structure of an XML document.
• VOTable ? XML document conform to the VOTable
  schema.

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VOTable Data Model

• VOTable hierarchy of Metadata associated
  TableData arranged as a set of Tables.
• Metadata Parameters Infos Descriptions
  Links Fields Groups.
• Table list of Fields Tabledata.
• TableData stream of Rows
• Row list of Cells.
• Cell Primitive (or variable-length list of
  Primitives, or multidimensional array of
  Primitives).
• Primitive integer, character, float, ...

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VOTable Structure
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VOTable Example

• lt?xml version"1.0"?gt
• ltVOTABLE version"1.1" xmlnsxsi"http//www.w3.or
  g/2001/XMLSchema-instance"
• xsinoNamespaceSchemaLocation"http//www.ivoa.ne
  t/xml/VOTable/VOTable/v1.1"gt
• ltCOOSYS ID"J2000" equinox"J2000."
  epoch"J2000." system"eq_FK5"/gt
• ltRESOURCE name"myFavouriteGalaxies"gt
• ltTABLE name"results"gt
• ltDESCRIPTIONgtVelocities and Distance
  estimationslt/DESCRIPTIONgt
• ltPARAM name"Telescope" datatype"float"
  ucd"phys.sizeinstr.tel"
• unit"m" value"3.6"/gt
• ltFIELD name"RA" ucd"pos.eq.rameta.main"
  ref"J2000"
• datatype" float" width"6"
  precision"2" unit"deg"/gt
• ltFIELD name"Dec" ucd"pos.eq.decmeta.main"
  ref"J2000"
• datatype"float" width"6"
  precision"2" unit"deg"/gt
• ltDATAgt
• ltTABLEDATAgt
• ltTRgtltTDgt010.68lt/TDgtltTDgt41.27lt/TDgtlt/TRgt
• ltTRgtltTDgt287.43lt/TDgtltTDgt-63.85lt/TDgtlt/TRgt
• lt/TABLEDATAgt
• lt/DATAgt

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ltVOTABLEgt

• Typically contains
• ltDESCRIPTIONgt, ltPARAMgt, ltINFOgt
• ltCOOSYSgt celestial coordinate system.
• ltRESOURCEgt description and data of logically
  independent data structures. Recursive.

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ltTABLEgt

• Contains
• DESCRIPTION element
• Collection of
• FIELD Description of a table column.
• PARAM constant value.
• GROUP Associate logically connected FIELDs or
  PARAMs
• LINK pointer to other documents or data servers.
• DATA rows of data. Containing cells in the same
  order as the FIELD definitions.

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ltFIELDgt

• Description of a table column.
• May contain DESCRIPTION, LINK and VALUES
  (information about domain of the data) elements.
• Attributes
• name/ID identify the FIELD. ID required if field
  has to be referenced.
• datatype nature of the data (how to read and
  store).
• arraysize if the column is used for storing more
  than one of the specified datatypes (10x5x).
• width precision number of characters
  numerical accuracy.

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ltFIELDgt cont.

• Attributes (cont.)
• unit units in which the values of the column are
  expressed (controlled vocabulary).
• ucd Unified Content Descriptor. Standarized
  classification of the physical quantity
  (pos.eq.ra)
• utype reference to an external data model
  (utypedatamodel_identifierrole_identifier)
• ref reference to other element.
• ltCOOSYS IDJ2000 equinoxJ2000 epochJ2000
  systemeq_FK5/gt
• ...
• ltFIELD nameRA ucdpos.eq.rameta.main
  refJ2000/gt

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datatypes
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ltPARAMgt

• Almost the same as ltFIELDgt
• Keeps a constant value.
• Same attributes as FIELD required attribute
  value.
• May be viewed as a FIELD that keeps a constant
  value.

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ltDATAgt

• Unique in the TABLE
• 3 possible formats
• TABLEDATA pure XML table.
• FITS
• BINARY for efficiency reasons
• FITS and BINARY must contain a ltSTREAMgt element.

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ltSTREAMgt

• Contains (or references) data not in XML format.
• Local data if encoding produces text.
• ltSTREAM encodingbase64gt
• AAAj/yVZiDGSSUwFZ6ypR4yGkADwAcQV0euAAIAAJBmMzNwZ
  WZmkGle4
• ..........
• lt/STREAMgt
• Remote data if encoding does not produce text or
  the data is too large.
• ltSTREAM hrefftp//sdc.laeff.esa.es/mydata.dat/
  gt
• ltSTREAM hreffile//sdc.laeff.esa.es/mydata.dat
  /gt
• ltSTREAM hrefhttp//sdc.laeff.esa.es/mydata.dat
  /gt

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Serialization
TABLEDATA
VOTable
TABLE
Encoding gzip base64 dynamic
EXTERNAL DATA
FITS
BINARY
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VOTable main elements
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Attributes
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VOTable in real world

• ConeSearch services.
• SSA (Simple Spectrum Access) SIA (Simple Image
  Access) services
• http//sdc.laeff.esa.es/ines/jsp/ssap.jsp?POS244
  .9,46.3SIZE0.5

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Tools

• Java libraries
• SAVOT http//cdsweb.u-strasbg.fr/devcorner.gml
• JAVOT http//www.us-vo.org/VOTable/JAVOT/
• C Libraries
• VO India http//vo.iucaa.ernet.in/voi/cplusparse
  r.htm
• Tools
• Aladin http//aladin.u-strasbg.fr/aladin.gml
• VOPlot http//vo.iucaa.ernet.in/voi/voplot.htm
• VOSpec http//pma.standby.vilspa.esa.es8080/vosp
  ec/index.html
• Topcat http//www.starlink.ac.uk/topcat