SSA V1.02 (updated in response to RFC)
dtody at nrao.edu
Wed Sep 19 06:37:44 PDT 2007
Hi All -
The SSA specification has been updated in response to the RFC.
The new version (V1.02) is available in the IVOA document repository
A summary of changes follows below.
Thanks to everyone who participated in the RFC; the specification is
much improved as a result of these careful reviews.
- Doug, Markus, and the SSA authors
SSA RFC Revisons
- Increased version number to 1.02.
- Added page numbers and a document title at the top of each page.
- Added TSAP use-case as Appendix A. Minor formatting changes.
- Updated example of standard metadata query response in Appendix C.
- Reworked and expanded the description of range-lists (8.7.2)
to clarify the semantics in response to questions from the RFC.
- Revised 4.1 to clarify the semantics of the mandatory query
parameters including support for theory data.
- Added a new section 8.7.3 on "Missing or null-valued parameters".
- Changed FLUXCALIB and WAVECALIB from boolean parameters to
string-valued parameters, with the values "absolute", "relative",
"normalized" (for WAVECALIB), and "any" (the default). The
minimum acceptable calibration is specified, hence specifying
"relative" will also find any data with an absolute calibration.
- Dataset.Collection specifies the IVOA identifier of the collection,
rather than the shortname.
- Changed the units of Access.DatasetSize from bytes to KB, to
emphasize that this is only intended to be an approximate estimate
of the dataset size, used for execution planning. During the
test implementations we have been having trouble getting people to
return this value, as they mistakenly thought that a precise value
was required. Switching to KB will emphasize this. The point was
clarified in the text as well.
- Added a new section 2.6 introducing the concept of dataset
identifiers. These are used later in the specification, but were
never really defined.
- Added a new section 2.9 "UTYPEs and UCDs" introducing these two
concepts and describing how they are used.
- Added SpectralAxis and FluxAxis to the Dataset metadata. Along with
the SI scaling factors, these are optional for fully compliant
spectra, but recommended ("should" provide) for native format spectra.
- In 4.2.4, added some additional discussion of how to deal with
multiple Associations, where the same query response record may
belong to more than one Association.
- In 220.127.116.11, when using the "@<field>" syntax to indicate an indirect
Association.Key (e.g., "@format"), the reference was changed to use
the VOTable ID of the table FIELD, rather than the UTYPE, to ensure
that the reference is unique in the event of multiple instances of
fields with the same UTYPE.
- In 4.1, added "If a service supports a parameter but the value
given cannot be parsed or is otherwise illegal (as opposed to merely
not matching any data) then an error response should be returned to
- In 18.104.22.168 (BAND), added text to the effect that "If the service
supports query by bandpass name but does not recognize an input
bandpass name, it should return an error indicating that it does
not recognize the named bandpass. If the service does not support
query by bandpass name but is called in this way, it should return
- In 8.2.1 clarified version number usage, and the relation of the SSA
and Spectrum version numbers.
- In 22.214.171.124, added a paragraph noting that the access reference string
should be URL encoded if it contains any reserved URL metacharacters
such as "#".
- Modified the specification of MTIME and added a new metadatum
Dataset.Deleted, to allow clients which use MTIME to track changes
to data collections to discover when a dataset has been deleted
(creation and modification were already supported). Dataset.Deleted
is only returned in a MTIME query. After an unspecified period of
time the service can permanently delete the reference to the deleted
dataset. (Note that there may be other reasons for persisting
dataset identifiers and associated dataset metadata, once such a
dataset identifier has been published; for now we merely support
client notification of deletion).
- In the description of the FORMAT parameter (4.1.1), added a note
that the FORMAT value is case insensitive. Also clarified that
FORMAT=fits refers to the SSA/Spectrum DM compliant FITS format,
and that "native" should be used to access a native project specific
FITS format, if any.
- In the section on the format=metadata query (6.1) added text to
clarify that FORMAT=metadata is a special case of the queryData
operation (this should be clear as the FORMAT parameter is part
of the queryData operation, but implementations showed that people
were confused about this). All operations must be specified
explicitly with REQUEST.
- In the TSAP discussion (Appendix A) it appears that what was called
a "getData" is actually a standard data query, hence the operation
name was changed to queryData. Also added REQUEST parameters to
the sample operations, as required by the protocol.
- I considered adding a new "Terminology" section as has been
discussed, but this would overlap too much with existing sections
such as on Levels of Compliance and Concepts, so I ended up
just adding some more material to the Concepts section, e.g.,
to define "dataset", "data collection", "service", "operation",
and so forth.
- In Characterization accuracy and error metadata table (126.96.36.199),
removed the "Accuracy." field from the *.Calibration UTYPEs, to
agree with changes to the Spectrum DM.
- The UTYPEs for the Char fill factor attributes all had to be changed
to Char.*.SamplingPrecision.SamplingPrecisionRefVal.FillFactor to
agree with changes in the Spectrum DM (surely a better/shorter
name could have been chosen, but it is probably too late to do
anything about this).
- Further minor changes to Appendix A (Theoretical Spectra)
were required to agree with the SSA spec, particularly in the
VOTables. Some of the UTYPEs and UCDs did not agree with the
current spec (e.g., Curation.PublisherID not Curation.PubID),
Collection is an IVOA identifier, and the like. There are
some "VOX:" UCDs still in this which might preferably be
locally-defined UTYPEs. Access.Format was changed from
"spectrum/votable" to "application/x-votable+xml". An xmlns:ssa
reference was added to the top of the VOTable.
- Added an Appendix D providing a summary of the SSA data model
(produced from my data model spreadsheet). This presents the whole
data model at a glance and includes things like datatype and
arraySize which are missing from the tables within the document.
- Modified 188.8.131.52 (BAND), where range-list syntax is first used, to
be more explicit about redirecting the user to section 8.7.2 for
details on the range list syntax.
- Tried to be more consistent in the use of fonts. The document font is
now used for anything which is a name (UTYPE, UCD, RESOURCE, FIELD,
PARAM, etc.), with a typewriter font used for literal examples of
computer text (e.g., a MIME type).
More information about the dal