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.

Separately from this meeting, from the US side, DougTody and JonathanMcDowell (the SSAP and SDM document editors) had also been discussing these proposed changes with the document authors and others via email.

We set forth the following goal: To create 1.1 versions (of SSA and the SpectrumDM) that attempt to fix or clarify what were seen as inconsistencies between the two documents. Mor extensive clarifications or additions could be added in a version 1.2. Big changes, possibly not backwards compatible, are postponed to 2.0 versions.

The rationale for this split is to have version 1.1 approved quickly and replace the current 1.0. A version 1.2 would permit more changes but would take significantly longer, gathering more extensive 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

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 "*":

Char.SpatialAxis.SamplingPrecision.SampleExtent Char.SpatialAxis.SamplingPrecision.FillFactor Char.SpectralAxis.SamplingPrecision.SampleExtent Char.SpectralAxis.SamplingPrecision.FillFactor Char.TimeAxis.SamplingPrecision.SampleExtent Char.TimeAxis.SamplingPrecision.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 Dataset.TimeSI time;arith.zp Char.SpatialAxis.Name meta.id Char.SpatialAxis.Ucd meta.ucd Char.SpatialAxis.Unit meta.unit

5 Misc. typos The SpectrumDM (on the FITS serialization section) should fix the following utypes:

Spectrum.Curation.ContactName -> Spectrum.Curation.Contact.Name Spectrum.Curation.ContactEmail -> Spectrum.Curation.Contact.Email Spectrum.Char.SpatialAxis.Accuracy.StatErr -> Spectrum.Char.SpatialAxis.Accuracy.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

Spectrum.Char.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