UCD inheritance in VOTables François Ochsenbein

11 May 2003 François Ochsenbein Summary 1. Alternative propositions 2. impact of the notion of column groups on UCD classification. In the very first version of VOTable 1yr ago the concept of UCDs was found as a good component in the metadata, but not really discussed.

11 May 2003 François Ochsenbein UCD History Started 5 years ago (P. Ortiz) in a bottom-up approach consisting of assigning a class to each VizieR column Started 5 years ago (P. Ortiz) in a bottom-up approach consisting of assigning a class to each VizieR column about 1500 classes representing the most frequent parameters found in the columns about 1500 classes representing the most frequent parameters found in the columns presented as a tree for just facilitating its understanding (like a book organized in chapters, a chapter in sections, etc...) presented as a tree for just facilitating its understanding (like a book organized in chapters, a chapter in sections, etc...)

11 May 2003 François Ochsenbein Problems and Proposals UCDs are: a- too many to find easily which UCDs to look at b- too few for matching accurate definitions c- difficult to retrieve (e.g. ID_VAR or VAR_ID ?) Proposed solutions: a+b: parametrized UCDs (Jonathan McDowell) c: 'atoms' (Guy Rixon)

11 May 2003 François Ochsenbein Parametrized UCDs (1) Rather complex scheme based on entities (1) about the universe: PHYS POP SAMPLE OBJ MED LOS (2) about our observations of the universe: SRC BKG OBS SURVEY EVENT (3) about our analysis of the observations: DATA REFER...

11 May 2003 François Ochsenbein Parametrized UCDs (2) _POS (astrometry) _PHOT (photometry) _SPEC (spectroscopy) _TIME (+date)... + parameter for more accurate definition For (1) and (2) specify what is observed: OBJ_PHOT SRC_PHOT BKG_PHOT SRC_PHOT_FLUX(250MHz)

11 May 2003 François Ochsenbein Parametrized UCDs (3) easy to understand easy to understand less definitions less definitions easily extensible via additional parameters easily extensible via additional parameters complex to assign SRC OBJ MED LOS several parameters in practice  how to define domains? ProsCons  we are examining how to reclassify with the distinction PHYS / SRC / INST (bottom-up approach)

11 May 2003 François Ochsenbein UCD Atoms Guy Rixon noted that many UCDs could be written as a combination of a few atoms or nouns, with additional qualifications like e.g. error min max class ID etc.  we are examining how far it can be implemented in VizieR

11 May 2003 François Ochsenbein Column Grouping close to the atom concept close to the atom concept can use the parameter concept can use the parameter concept was already mentioned in the first meeting (Strasbourg, January 2002) as a possible improvement of VOTable to specify that e.g. (X,Y) are the 2 components of a vector

11 May 2003 François Ochsenbein Value of the flux at 8.6GHz <FIELD ID="e_Flux1" name="errFlux1" ucd="ERROR" datatype="float" unit="mJy"> Error on flux values, both at 8.6 and 7.5GHz <PARAMETER ID="Freq1" name="Frequency" value="8.62" datatype="float" ucd="SPECT_LINE_FREQUENCY" unit="GHz" /> Value of the flux at 7.5GHz <PARAMETER ID="Freq2" name="Frequency" value="7.55" datatype="float" ucd="SPECT_LINE_FREQUENCY" unit="GHz" />

11 May 2003 François Ochsenbein VOTable Groups Notion of atoms: UCD inheritance from group to field Notion of atoms: UCD inheritance from group to field Notion of parametrization: one or more parameters can be associated to a group Notion of parametrization: one or more parameters can be associated to a group e_Flux1 is ERROR of PHOT_FLUX_RADIO_8.4G e_Flux1 is ERROR of PHOT_FLUX_RADIO(8.6GHz)

11 May 2003 François Ochsenbein How far can we go ? Adding parameters is fine, but should we remove e.g. any information about frequency and write or which granularity to keep in the UCD? PHOT_FLUX_RADIO_cm or PHOT_FLUX_RADIO_1.4G

11 May 2003 François Ochsenbein How far ? parameters are not required parameters are not required we still have to assess whether fields are comparable we still have to assess whether fields are comparable but the best granularity level has to be defined. I would plea for rather accurate UCDs – something like at least one UCD for each frequency doubling

11 May 2003 François Ochsenbein Remarks on VOTable groups the group associates columns not just UCDs – which is more accurate since several fields can share the same UCD. the group associates columns not just UCDs – which is more accurate since several fields can share the same UCD. Any field may have an associated parameter, a group can obviously consist in a single field. Any field may have an associated parameter, a group can obviously consist in a single field. a field may belong to several groups (ref attribute) a field may belong to several groups (ref attribute) it could be imagined several levels of inheritance, i.e. that a can contain a  abritrary complex structures it could be imagined several levels of inheritance, i.e. that a can contain a  abritrary complex structures

11 May 2003 François Ochsenbein Position along the X-axis of the CCD Position along the Y-axis of the CCD Example of a possible complex group

11 May 2003 François Ochsenbein Concluding remarks Groups in VOTable are bringing accuracy Groups in VOTable are bringing accuracy Groups in VOTable are a natural way to introduce the atoms and UCD inheritance Groups in VOTable are a natural way to introduce the atoms and UCD inheritance To discuss later in this meeting ? To discuss later in this meeting ?