[CITE-Forum] Self join without aliases: valid?

Andrea Aime andrea.aime at geo-solutions.it
Wed Mar 21 09:31:04 EDT 2018

the CITE test engine is generating the following request:

<?xml version="1.0"?><wfs:GetFeature
xmlns:wfs="http://www.opengis.net/wfs/2.0" count="10" service="WFS"
startIndex="0" version="2.0.0">
  <wfs:Query xmlns:ns50="http://cite.opengeospatial.org/gmlsf"
typeNames="ns50:PrimitiveGeoFeature ns50:PrimitiveGeoFeature">
    <Filter xmlns="http://www.opengis.net/fes/2.0">

Now, as you can see, it's a self join, but does not contain any alias
declaration. As stated, software could be (imho) legitimately
think it's not actually a join, and that the two fiters are both referring
to the first "instance" of the feature type.

I've checked the specification, all self join examples use aliases, but I
do not see a clear request to use aliases on self-join.
Referencing a significant bit (from "query the feature types
aliases parameter"):

Aliases are typically used in query expressions, that perform a join
operation (see, to support self-
joins. That is a join of one feature type back to itself.

typeNames="myns:Feat1 myns:Feat1" aliases="a b"

In this example, the first feature type, myns:Feat1, is aliased to the name
"a" and the second feature type, myns:Feat1, is
aliased to the name "b". Thus properties from the first instance of
myns:Feat1 can be referenced in a request as
"/a/property_name" and properties from the second instance of myns:Feat1
can be referenced in a request as
"/b/property_name" where the token "property_name" is used as a place
holder for the name of any property of the feature

So... can anybody clarifiy if this is an issue in the test engine, or if
the servers are indeed supposed to understand
the above request?


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Ing. Andrea Aime
Technical Lead

GeoSolutions S.A.S.
Via di Montramito 3/A
55054  Massarosa (LU)
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