On Tue, May 23, 2017 at 3:00 AM, Luca Morandini <lmorand...@ieee.org> wrote:
> Folks,
>
> I am developing a datastore for SDMX data sources (clearly, a geometryless
> one).
> It kind of works, with CQL/XML filters used to bind the dimensions to
> values and
> choose the one measure to return.
>
> However, I don't really know how to return the list of members of a
> dimension,
> list which is necessary to build the filter.
>
> For instance, before selecting all the male resident population of a
> certain
> country, I need to know the members of the "Gender" dimension, the list of
> all
> measures available, and the members of the "Country" dimension as well.
>
Code wise, this is normally done by running a feature visitor on a
collection. Well known
feature visitors such as count and distinct are normally optimized away
in the store and computed in a more efficient way (think "select distinct"
in a relational
database).
However, WFS cannot expose those results, because an aggregation breaks the
XML schema of the results and there is no way to call aggregates to start
with.
So that is normally exposed by WPS processes that do exactly that, check the
UniqueProcess in WPS (it actually runs a UniqueVisitor against the store,
and the store can optimize it).
If you want to use solely WFS, then exposing a side table seems indeed an
option.
Cheers
Andrea
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