Mapping of TAP_SCHEMA.columns.principal to SCS VERB

[Marco Molinaro]

Hi Walter,
taking freely from latest TAP PR (work in progress), but the concepts
remain the same as the ones in TAP-1.0:

==
The principal, indexed, and std columns are boolean values implemented
as integers. As such, the value must be 0 or 1; no other values are allowed.

The principal flag indicates that the column is considered a core part
of the content; clients can use this hint to make the principal column(s)
visible, for example by selecting them by default in generating an ADQL
query. In cases where the service selects the columns to return (such as a
query language without an explicit output selection), the principal column
indicates those columns that are returned by default.
==

So, there's no intention, I think, to make it map VERB or trying to set
up a set of levels of principal, it's simply a flag to declare a column as
a special one among others.

Cheers,
    Marco

2017-10-10 0:32 GMT+02:00 Walter Landry <wlandry at caltech.edu>:

> Hi Everyone,
>
> In the current TAP PR, TAP_SCHEMA.columns.principal is an integer.  Is
> the intention to make that map to the same meaning as SCS's VERB?  It
> seems that the meaning is somewhat inverted.  So
>
> SCS VERB    TAP principal
> 1           2
> 2           1
> 3           0
>
> If that is the case, should the meaning (and perhaps the actual
> mapping) be put into the TAP PR?  To be concrete, the wording could be
>
>   The "principal" number indicates the importance of a column. Clients
>   can use this hint to make some columns visible, for example by
>   selecting them by default in generating an ADQL query.  A value of
>   '2' is for columns that the provider considers a bare minimum that
>   are useful in describing the returned objects.  A value of '1' is
>   for columns that may be generally useful, but not always necessary.
>   A value of '0' is for columns that are probably only of use to
>   specialized audiences.  These values correspond to VERB levels 1, 2,
>   and 3 in Simple Cone Search (Plante & Molinaro et al 2017).
>
> Thanks,
> Walter Landry
>
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