[p3t] A "model-based" approach

[Paul Harrison]

Hi,

Another way of thinking about abstracting the meaning/functionality of various services is to think of the service as an API to manipulate and query an underlying data model – UWS is a data model of a job queue with an associated API. The IVOA already has a standard way of describing data models, namely VO-DML, which is why I put the link that I did on the P3T wiki page as a potential starting point for the formal description of service APIs as a step to formalizing the “schema” part of the openAPI specification of the interface – the VO-DML tooling already has a JSON serialization of the data models as well as an XML serialization.

UWS is slightly unusual amongst IVOA protocols in that its response is not a VOTable – TAP obviously needs its main response to use a table data model, but there are other services – e.g. datalink where the response (especially in the case of templating and specifying parameters), where it is fairly unnatural to try to express the intention in a table model. There is a standard way (MIVOT) of expressing a data model in VOTable, but it does take quite a lot of parsing. Previous attempts to try to express the VOTable model in JSON have not been able to reach a satisfactory conclusion, but perhaps in some cases it might be a cleaner route to JSON to express the intended output in the “natural” data model rather than going via a tabular expression of that model.

There are some other aspects of DM use in IVOA – e.g. the same or similar concepts appearing in several models that would also benefit from some rationalization, but I think that is outside the remit of this group.

Paul.

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