STC2:Meas Proposed Recommendation: Request for CommentsWATCHOUT : This RFC page replaces RFC#1 Rationale for a second RFC round:
SummaryVersion 1 of STC was developed in 2007, prior to the development and adoption of vo-dml modeling practices. As we progress to the development of vo-dml compliant component models, it is necessary to revisit those models which define core content. Additionally, the scope of the STC-1.0 model is very broad, making a complete implementation and development of validators, very difficult. As such it may be prudent to break the content of STC-1.0 into component models itself, which as a group, cover the scope of the original. This effort will start from first principles with respect to defining a specific project use-case, from which requirements will be drawn, satisfied by the model, and implemented in the use-case. We will make use of the original model to ensure that the coverage of concepts is complete and that the models will be compatible. However, the form and structure may be quite different. This model will use vo-dml modeling practices, and model elements may be structured differently to more efficiently represent the concepts. This model covers the description of measured or determined astronomical data, and includes the following concepts:
Implementation Requirements(from DM Working group twiki): The "IVOA Document Standards" standard has a broad outline of the implementation requirements for IVOA standards. These requirements fit best into the higher level standards for applications and protocols than for data models themselves. At the Oct 2017 interop in Trieste, the following implementation requirements for Data Model Standards was agreed upon, which allow the models to be vetted against their requirements and use cases, without needing full science use cases to be implemented.
Serializations:
Software:
ValidatorsAs noted above, the serializations may be validated to various degrees using the corresponding schema
Links with CoordsThe Measurement model is heavily dependent on the Coordinates model (also in RFC) for its core elements. Information about its relation to the Coordinates model, and how the requirements are distributed can be found on the STC2 pageComments from the IVOA Community during RFC/TCG review period: 2020-10-26 - 2020-12-07Comments by Markus DemleitnerThe introduction and points (1), (4), (7), (11) from my RFC 1 comments I'd still retain, and I essentially stand by the summary, which I'd update to: I'd make the model a lot smaller, thus creating space we'll need once we tackle strict errors (i.e., explicit distributions) in earnest one day. We ought to have, perhaps NaiveMeasuremetnt (a pseudo-distribution saying "value is something like an expectation or perhaps a median, and error is something like a first moment or something like that), and perhaps AsymmetricNaiveMeasure. I'm not even convinced we have credible use cases for statError and sysError. And if we want correlations, these should be explicit as relations between, I guess, measurements (or their parameters?). The way to exercise that is to have a few data centers annotate a representative part of their tables; I'm not saying they need to be able to precisely annotate everything -- if it's enough for the "automatically plot error bars" use case, I'd say that's a success on which we can build. On the changes since PR1, the recent addition "The current model assumes Gaussian distributions with shapes defined at the 68% confidence level" we really shouldn't do -- it's a lot more than we can confidently claim about most of our data holdings. At this point, I think we can only say "what we're doing here are rough error bars". Going for actual distributions is something for when we know what we'll do with them, and an "automatic error propagation" use case, to me, is a bit ambitious when we can't even plot error bars at this time. Adding to point (4) of the original RFC comments -- that we shouldn't have Time, Position, Velocity, ProperMotion, and Polarization as separate classes, but instead distinguish physics by UCD as elsewhere in the VO -- people have said that's a serialisation issue; well, it's not in our current plans, where the DM types would directly sit on VOTable elements. This means that both UCD and DM type would do about the same thing. Let's avoid that. Since I can't make out a use case for why something figuring out distributions would actually need to know physics, my preference would be to keep the whole notion outside of measurements in the first place. If such a use case were identified, I'd say adding a UCD attribute would be ok, with the understanding that some magic in our VOTable mapping would make that the UCD of the annotated FIELD, PARAM, or GROUP. -- MarkusDemleitner - 2020-11-25Comments from TCG member during the RFC/TCG Review Period: 2020-10-10 - 2020-12-07WG chairs or vice chairs must read the Document, provide comments if any (including on topics not directly linked to the Group matters) or indicate that they have no comment. IG chairs or vice chairs are also encouraged to do the same, althought their inputs are not compulsory.TCG Chair & Vice ChairApplications Working GroupData Access Layer Working GroupData Model Working GroupGrid & Web Services Working GroupRegistry Working GroupSemantics Working GroupData Curation & Preservation Interest Group | |||||||||||||||||||||||||||||||||||||||||||||||||||
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Solar System Interest GroupTheory Interest GroupTime Domain Interest GroupOperationsStandards and Processes CommitteeTCG Vote : Vote_start_date - Vote_end_dateIf you have minor comments (typos) on the last version of the document please indicate it in the Comments column of the table and post them in the TCG comments section above with the date.
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