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SOURCE - simple test cases

From: Seaborne, Andy <andy.seaborne@hp.com>
Date: Mon, 27 Sep 2004 16:57:30 +0100
Message-ID: <8D5B24B83C6A2E4B9E7EE5FA82627DC93966FF@sdcexcea01.emea.cpqcorp.net>
To: <public-rdf-dawg@w3.org>

To start some test cases for SOURCE, here is one of the simplest I could
think of:

	Andy

-----------------------------

---- Graph <u1>
:a :b :c

---- Graph <u2>
:a :b :c

-----------------------------

---- Query 1
SELECT *
FROM <u1>, <u2>
WHERE (?x ?y ?z)


I expect one result:

?x = :a , ?y = :b , ?z = :c

A direct implementation of quads (where slot 4 is either the statement
id or the context) might well yield two results which have the same
?x/?y/?z - I'm assuming that the query is on the RDF merge of the
documents identified by <u1> and <u2>. I'm also assuming that the target
for the query may be specified by context and not an explicit FROM -
actually, I expect this to be quite common.

I know some implementations have more results than this because it
includes "system" information or other information not part of the
original <u1> and <u2>.  presumably, these are implementation dependent
and outside exhaustive definition by DAWG.

---- Query 2

SELECT *
FROM <u1>, <u2>
WHERE SOURCE ?src (?x ?y ?z)

Here, I'd expect that there are two results:

?src=<u1> , ?x = :a , ?y = :b , ?z = :c
?src=<u2> , ?x = :a , ?y = :b , ?z = :c

Adding "SOURCE ?src" increases the number of solutions because the query
is now over each of the components.

---- Query 2

SELECT ?x ?y ?z
FROM <u1>, <u2>
WHERE SOURCE ?src (?x ?y ?z)

This is just the projection in the SELECT of query 2. I'd expect that
there are two results:

?x = :a , ?y = :b , ?z = :c
?x = :a , ?y = :b , ?z = :c

Any interaction with having SELECT DISTINCT or COUNT is a separate
matter.

---- ----

For a single source:

---- Graph <v>
:a :b :c

---- Query 3
SELECT *
FROM <v>
WHERE (?x ?y ?z)

One result:

?x = :a , ?y = :b , ?z = :c

---- Query 3
SELECT *
FROM <v>
WHERE SOURCE ?src (?x ?y ?z)

One result:

?src = <v> , ?x = :a , ?y = :b , ?z = :c

treating a single named component the same.

---- ----

Finally, this brings the case where the external context provides a
single, unnamed graph.  There is no "FROM" clause.  This is Eric's "?src
= null" case I think.  The test query involves:

SOURCE ?src (?x ?y ?z)

which could yield:

?x = :a , ?y = :b , ?z = :c

that is, ?src is not bound but there is a solution. If ?src is used
else, it can bind and that makes this a problem.  Not sure the best
solution.  Other choices include having no solution (argument; there
isn't a named component of the overall RDF graph that matches), a
special symbol URI http://www.w3.org/2001/sw/DataAccess/Unknown (seems
to have special handling) or a bNode (which implies the source *as a
document* not a graph is in the set of all individuals - not sure if
that's legal or not).  Not sure in which graph the bNode exists - it
isn't in the original graph supplied and there is no other graph around
except some "system graph".

Having written that, I'm inclined to keep things simple in the
conceptual model - no match here because there is no named source.

Hope this helps - Andy
Received on Monday, 27 September 2004 15:58:02 GMT

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