SSAP 1.1 collaborative page
At the
EuroVO AIDA a small group of people interested in updating the
SSA and
SpectrumDM document gathered. Participants;
BrunoRino,
KeithNoddle (DAL chair),
MireilleLouys (DM chair),
AlbertoMicol,
IgorChilingarian,
JesusSalgado,
FrancoisBonnarel.
After this meeting and after formal communication, from the US side,
DougTody and
JonathanMcDowell have been already discussing about these proposed changes as SSAP/SDM editors.
We set forth the following goal: To create 1.1 versions (of SSA and
SpectrumDM) that attempt to fix the inconsistencies between the two
documents. Clarifications and small additions should be added in
versions 1.2. Big changes, possibly not backwards compatible, are
postponed to 2.0 versions.
The rationale for this split is to have versions 1.1 approved quickly
and replace the current 1.0. Versions 1.2 will take significantly
longer, gathering much input from the community.
In both cases (1.1. and 1.2) the assumption is that no existing
application should break. This means that when a fix creates potential
breakage, the potentially affected applications should be consulted.
Below, the result of our discussion on what must be changed in order to reach version 1.1. We were lucky enough to have both the DM and DAL
Working Group leads; we concluded that after a short period of time
after circulating these meeting minutes to the relevant lists, Working
Drafts should be produced, ahead of the May interop in Victoria.
SSAP/SDM inconsistencies
BrunoRino (26/03/10) analysis:
1.
The SSA data model is derived, but decoupled, from the SpectrumDM
The acknowledged divergences are:
- "required" flags (Mandatory, Recommended, Optional) are different
- the SSA data model contains service related metadata, that have no
meaning for the
SpectrumDM
- the
SpectrumDM contains metadata related to data analysis (Data.*)
that are of no interest for data discovery (which is the purpose of SSA)
- in SSA, the "Spectrum." prefix found in the
SpectrumDM utypes was
dropped, and in some cases a "Dataset." prefix was added.
Even if those divergences are discrepancies, they are not going to be
fixed in a 1.x document. Instead, SSA Section 2.2 ("Data Model") must be changed to reflect these divergences. It should state explicitly that a reader of the SSA should only refer to the
SpectrumDM to seek
clarification about the meaning of metadata fields. The specification of required fields, the UCDs, and even the utype syntax for setting up a SSA server are to be read from the SSA document. Metadata defined in the
SpectrumDM, but not listed in the SSA, are not relevant for SSA service interface.
This is a compromise towards reaching rapidly a stable revision of the
documents. We would much prefer to have a single source for the
definition of the datamodel, which the SSA protocol would just extend.
But we believe this is too large of a task to achieve while maintaining backwards compatibility, on a reasonable time-scale.
2.
The use of "*" and ".." in UCDs
This must be eliminated.
These characters are always used in the context of "em.*" or "em...".
Our understanding is that these characters are placeholders, which a
data provider must fill in, according to its requirements. A list of all possible values and meanings must be provided instead, using the
following primary UCDs:
em.wl
em.freq
em.energy
3.
The use of "*" in utypes
This must be eliminated. The correct utypes to use are the ones in the
"Query Response" section of SSA, but without the "*":
SampleExtent
FillFactor
SampleExtent
FillFactor
SampleExtent
FillFactor
4.
Missing UCDs in SSA
The SSA is correct, the
SpectrumDM should not have a UCD for the
following elements (the UCDs provided in the
SpectrumDM on those
elements are either wrong or confusing):
utype UCD to be removed
TimeSI time;arith.zp
SpatialAxis.Name meta.id
SpatialAxis.Ucd meta.ucd
SpatialAxis.Unit meta.unit
5
Misc. typos
The
SpectrumDM (on the FITS serialization section) should fix the
following utypes:
ContactName -> Spectrum.Curation.Contact.Name
ContactEmail -> Spectrum.Curation.Contact.Email
StatErr ->
StatError
The SSA should fix the following UCD:
em;spec.binSize -> em;spect.binSize
Extra spaces in UCDs and utypes are typos and should be removed
6.
Dimensional analysis typo
In the
SpectrumDM, change (from 10-10 to 1E-10) the way to express
exponents within the dimensional analysis elements
Section 3.2 should read:
Pedro Osuna and Jesus Salgado have proposed a representation in the
spirit of dimensional analysis, using the symbols M, L, T to signify kg,
m, s respectively and omitting the ** for powers, so that
10**3 Jy Hz
which is equivalent to
10**-23 kg s**-2
is written compactly as
1E-23MT-2
and the example in section 9.4:
SPECSDIM= '1E-10 L' / Spectral SIDim
FLUXSDIM= '1E+7 ML-1T-3' / Flux SDim
7.
Wrong UCDs
SpectralAxis.Coverage.Location.Value has a wrong UCD of
instr.bandpass.
It should become the following list (in accordance to point 2 above):
em.wl;instr.bandpass
em.freq;instr.bandpass
em.energy;instr.bandpass
8.
Inconsistencies within the SSA itself
Add the Dataset.Deleted utype to Appendix D.
Remove the Data.* utypes from Appendix D.
Add the remaining missing utypes present in Appendix D to section 4.2
(the list is too long and too boring to show here)
9.
Inconsistencies within the SpectrumDM itself
Add a comment to the FITS serialisation stating that it does not cover
the whole of the
SpectrumDM utypes
Note:
The "consolidation" activities detailed in points 7 and 8 should also
make sure the order by which the utypes are listed is consistent
throughout all documents.
See also:
http://www.ivoa.net/internal/IVOA/IvoaExecMeetingFM34/SSA_SDM_assessment.xls