VOTable agenda

1
VOTable agenda

• News from Applications
• VOTable Schema
• VOTable expression units, datatypes...
• Utype
• Other topic ?

2
Where are we ?

• VOTable1.1 is 2 years old
• quite generally used, many tools
• General referencing to external data models
  attempted at last El Escorial meeting, without
  success...

3
News from Applications

• Heard about
• VOPlot v1.2.1 (source code available)
• VOTable Streaming Writer v1.1
• VOMegaPlot 1.0
• TOPCAT v2.1
• Some problems heard about input/output of
  VOTables
• conservation of GROUP structures (TOPcat)
• ... ?

4
VOTable schema

• Embedded spaces nbsp vs 32 or x20
• Recursivity allowed in RESOURCE GROUP and OPTION
• How does it work in VOTable utilities (e.g.
  TOPcat VOPlot VOFilter...) a single resource ?
• It is useful, can describe trees instead of
  simple arrays
• Used in some applications (instrument apertures)
• is/will these limitations in the used tools be
  removed?
• What to do ? ltRESOURCE type"notRecursive"gt

5
VOTable expressions

• Sexagesimal necessary ? useful ?
• concerns only the ltTABLEDATAgt serialisation
• Way adopted at CDS
• ltFIELD name"RAJ2000" ucd"pos.eq.rameta.main"
  ref"J2000" datatype"double" width"11"
  unit"quothmsquot"gt
• Date/Time
• accept JD, MJD, decimal year, ISO...?
• specify in some unit ?
• Must agree on common solutions across VO
  components

6
VOTable expressions (cont'd)

• Units should not the rules be identical in the
  various VO components ?
• cm/s2 cms(-2) cm.s-2 cm s-2 ...
• should standardize across VO components!!!
• Explicit and detailed reference is given in
  VOTable document (no blank, no asterisk)
• "special" quoted units -- should be extended
  toward other exotic units like electromagneticCGS
  or Crab??
• Must agree on common solutions across VO
  components

7
Utypes what is it ?

• Non-mandatory attribute of RESOURCE TABLE FIELD
  PARAM GROUP
• originally created for DAL needs
• is a possible attribute in VOTable1.1 wherever
  the ucd is an acceptable attribute
• contrary to the ucd, gives a fully detailed
  meaning of the field, parameter or group
• ucd broad semantics, typically used for data
  mining
• utype detailed semantics, refers to a data model

8
Utype its usage in VOTable

• can supply an exact description of the column
  contents
• immediate application for a referencing of
  parameters which exact meaning is crucial
• systems of coordinates celestial, terrestrial,
  solar, ... (connection with STC)
• time definitions (connection with STC)
• photometric systems bandpasses
• more generally any parameter in a model,
  simulation...

9
Status after El Escorial meeting

• proposal of using in the utype attribute an XPath
  analogy to refer accurately to the parameter in
  the data model e.g.

ltFIELD name"RAJ2000" datatype"double" utype"c
rdAstroCoords_at_coord_system_id'J2000-OPTICAL-ET'
/ Position2D/Value2(1)"gt lt/FIELDgt ltFIELD
name"DEJ2000" datatype"double" utype"crdAstro
Coords_at_coord_system_id'J2000-OPTICAL-ET'/
Position2D/Value2(2)"gt lt/FIELDgt
? essentially refused
10
What changed since El Escorial

• STC 1.30 does not require any more to give the
  components of a position as an array
• ? definition of a utype for position easier
• utype role could be somewhat clarified through
  restricted discussions between DAL, DM and
  VOtable groups

11
utype clarifications

• Definition utype piece to reference a component
  of an external data model.
• differences between static or dynamic data
  models
• static data model (compile-time) every
  component defined in the data model examples
• SSA contains only static models
• circular target region is static
• dynamic data model (run-time) components may
  be added examples
• Characterization may have axises defined by
  their ucd.
• polygonal region may have any number of vertices
  ?3

12
Examples in STC
ltstcCirclegt ltstcCenter unit"deg"gt
ltstcC1gt233.737917lt/stcC1gt
ltstcC2gt23.503330lt/stcC2gt lt/stcCentergt
ltstcRadius pos_unit"arcsec"gt10.0lt/stcRadiusgt lt/
stcCirclegt

• Static model
• Dynamic

ltstcPolygongt ltstcVertexgt ltstcPositiongt
ltstcC1gt233.737917lt/stcC1gt
ltstcC2gt23.503330lt/stcC2gt lt/stcPositiongtlt/stc
Vertexgt ltstcVertexgt ltstcPositiongt ...
... ... ... lt/stcPolygongt
13
Scenarios for utype assignation

• XPath way applies to dynamic data models
  crdAstroCoords_at_coord_system_id'J2000
  -OPTICAL-ET'/Position2D/C1
• ... but gives complex strings, and was refused...
• DAL way ssaSky.Resolution
• a simple rule is defined to derive the utype
  contents (concatenation of elements' names with
  dots e.g.
• is restricted to static data models
• define the recommended utype in the model ?
• should converge to common solutions across VO
  components

14
Example for STC circular region
ltFIELD ID"Col1" name"cRA"
utype"stcCircle.Center.C1" ucd"pos.eq.ra"
unit"deg" datatype"double" /gt ltFIELD ID"Col2"
name"cDec" utype"stcCircle.Center.C2"
ucd"pos.eq.dec" unit"deg" datatype"double"
/gt ltPARAM name"targetRadius"
utype"stcCircle.Radius" ucd"pos.angDistance"
datatype"double" unit"arcsec" value"12" /gt
15
Example for STC polygon
ltGROUP name"myPolygon" utype"stcPolygon"gt
ltFIELDref ref"vert1"gt ltFIELDref ref"vert2"gt
ltFIELDref ref"vert3"gt ltFIELDref
ref"vert4"gt lt/GROUPgt ltFIELD ID"Vert1"
name"point1" utype"stcPolygon.Vertex"
ucd"pos.eq" unit"deg" arraysize"2"
datatype"double" /gt ltFIELD ID"Vert2"
name"point2" utype"stcPolygon.Vertex"
ucd"pos.eq" unit"deg" arraysize"2"
datatype"double" /gt ...
16
Example for Coordinates
ltGROUP ucd"pos.eq" utype"stcAstroCoords" gt
ltPARAM utype"stcAstroCoords.coord_system_id"
datatype"char" arraysize""
value"UTC-FK5-TOPO" /gt ltFIELDref ref"Col1"
/gt ltFIELDref ref"Col2" /gt lt/GROUPgt ltFIELD
ID"Col1" utype"stcAstroCoords.Position2D.C1"
ucd"pos.eq.ra" name"RA" unit"deg"
datatype"double" /gt ltFIELD ID"Col2"
utype"stcAstroCoords.Position2D.C2"
ucd"pos.eq.dec" name"Dec" unit"deg"
datatype"double" /gt
17
Example for Characterization
ltGROUP utype"charSpectralAxis" gt ltPARAM
utype"AxisFrame.ucd" datatype"char"
arraysize"" value"em" /gt ltFIELDref
ref"Col1" /gt lt/GROUPgt ltFIELD ID"Col1"
utype"Coverage.Location" unit"nm"
ucd"em.wl" name"lambda" datatype"double" /gt
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19
A1. LINK Questions

• LINK is required for several applications
• SIAP one of the columns gives a link to actual
  image server, coded in a ltTDgtlt!CDATA.......gtlt/
  TDgt
• Aladin required to provide a link to the full
  data, coded in a LINK with substitutions
• other usage ?
• ? It is important !

20
LINK substitution(Aladin way)

• ltLINK href"http//ivoa.net/lookup?GalaxyName
  ampRARAampDEDE"/gt
• a substitution filter is applied in the context
  of a particular row. For the first row of the
  table, the substitution would result in the URL
• http//ivoa.net/lookup?GalaxyN224RA010.68DE
  2b41.27

21
LINK definition(INES way)

• ltFIELD name"Spectrum" datatype"char"
  arraysize""gt
• ltDESCRIPTIONgt
• Link to the spectrum file
• lt/DESCRIPTIONgt
• ....
• ltTDgtltSTREAM href"http//ivoa.net/getSpectrum?Name
  "N224"/gt
• lt/TDgt
• .

22
A2 Query Extension

• It is another view on the LINK present the
  different parameters available for a query.
• Role of the registry ?
• these details stored in a "fine-grain" registry
• in the context of a "coarse-grain" registry, some
  facility of getting these details must exist...

23
A3 Arrays of variable-length strings

• Is related to the String datatype which does not
  exist in VOTable (FITS syndrome)
• FITS knows only a fixed-size array of
  variable-length strings (via the "Variable length
  array" convention)

24
A4 - FIELDs as data pointers

• when a column contains a reference or a pointer
  to the data URLI, cid (Content-ID), ...
• http//almasw.hq.eso.org/almasw/bin/view/Archive/V
  OTableDataTransfer
• Add type"location" attribute to ltFIELDgt
• Add type"location" attribute to ltLINKgt

25
A5 - Encoding individual table cells

• To decide to insert binary data at the cell level
  typically an image
• without the need for a break in the stream
• without having to encode the whole table

26

• ltTABLE name"SpectroLog"gt
• ltFIELD name"Target" ucd"meta.id"
  datatype"char" arraysize"30"/gt
• ltFIELD name"Instr" ucd"instr.setup"
  datatype"char" arraysize"5"/gt
• ltFIELD name"Dur" ucd"time.expo" datatype"int"
  width"5" unit"s"/gt
• ltFIELD name"Spectrum" ucd"phot.fluxDensity"
  datatype"float" arraysize""
• unit"mW/m2/nm" precision"E3"/gt
• ltDATAgtltTABLEDATAgt
• ltTRgtltTDgtNGC6543lt/TDgtltTDgtSWS06lt/TDgtltTDgt2028lt/TDgtltTD
  encoding"base64"gt
• QJKPXECHvndAgMScQHul40CSLQ5ArocrQLxiTkC3XClAq0OWQK
  QIMUCblYFAh753QGij10BT
• Em9ARKwIQExqf0BqbphAieuFQJS0OUCJWBBAhcrBQJMzM0CmRa
  JAuRaHQLWZmkCyhytAunbJ
• QLN87kC26XlA1KwIQOud0DsWh1A5an8QN0m6UDOVgRAxO2RQM
  9Lx0Din75A3o9cQMPfO0C/
• dLxAvUeuQKN87kCXQ5ZAjFodQH0vG0B/jVBAgaHLQI7Ag0CiyL
  RAqBBiQLaXjUDYcrBA8p
• QPcKPUDg7ZFAwcKPQLafvkDDlYFA1T99QM2BBkCs3S9AjLxqQI
  SDEkCO6XlAmlYEQKibpkC5
• wo9AvKPXQLGBBkCs9cNAuGp/QL0euEC4crBAuR64QL6PXEDOTd
  NA2987QN9TEDoMSdA8mZm
• QOZumEDDZFpAmmZmQGlYEEBa4UhAivGqQLel40Dgan9A4WBCQL
  NcKUCIKPZAk1P4QNWRaEEP
• kWhBKaHLQTkOVkFEan9BUWBCQVyfvg
• lt/TDgtlt/TRgt
• lt/TABLEDATAgtlt/DATAgt
• lt/TABLEgt

27
A6 - Very large arrays

• The BINARY serialization of variable-length
  arrays uses a 4-byte prefix for the number of
  items of the array. This convention imposes an
  absolute maximal number of 231
• Possibility of an arrayprefix which could specify
  the size of the number of items
• arrayprefix"unsignedChar" would imply max. 255
  elements in the array
• arrayprefix"long" would accept gt 2billion items

28
A7 - Additional TABLE attributes

• ucd and utype attributes ?
• (were adopted)

29
A8 - A new CSV serialization ?
Data structure widely interpretable
ltTABLE name"Messier"gt ltFIELD name"Number"
ID"M" ucd"meta.id" datatype"int"
gt ltDESCRIPTIONgtMessier Numberlt/DESCRIPTIONgtlt/FIELD
gt ltFIELD name"R.A.2000" ID"RA" ucd"pos.eq.ra"
ref"J2000" unit"deg"
datatype"float" width"5" precision"1"
/gt ltFIELD name"Dec.2000" ID"DE"
ucd"pos.eq.dec" ref"J2000" unit"deg"
datatype"float" width"5" precision"1"
/gt ltFIELD ID"T" name"Classification"
datatype"char" arraysize"10"
ucd"src.class"gt ltDESCRIPTIONgtClassification
(galaxy, glubular cluster, etc)lt/DESCRIPTIONgtlt/FIE
LDgt ltDATAgtltCSV headlines"1"gtlt!CDATA M RA DE Cla
ssification 3 205.5 28.4 Globular
Cluster 31 010.7 41.3 Galaxy gtlt/CSVgtlt/DATAgt lt/T
ABLEgt
30
Conclusions ?

• Agreement of common conventions (units,
  date/time, sexagesimal,...) with other WG
• Agreement of utype syntax/definition with other
  WG
• Rewrite the VOTable schema ? VOTable1.2
• Appendices ? ?

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Question of Astrometry Definition

• Current VOTable way (from V1.0)
• ltCOOSYS ID"J2000" system"eq_FK5"
  equinox"J2000" epoch"J1991.25"/gt
• Does not apply to e.g. solar studies, moving
  frames -- VOTable has to be more generic
• VO components have to be shared --- if STC is the
  data model of spacetime coordinates, VOTable as
  well as other VO components has to refer to it.