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RE: RDF query testcases? (RDQL/Jena testing overview)

From: Seaborne, Andy <Andy_Seaborne@hplb.hpl.hp.com>
Date: Fri, 17 Jan 2003 10:56:30 -0000
Message-ID: <5E13A1874524D411A876006008CD059F038D40A6@0-mail-1.hpl.hp.com>
To: Jeen Broekstra <jeen.broekstra@aidministrator.nl>
Cc: www-rdf-rules <www-rdf-rules@w3.org>

Jeen wrote:

>I'll have a look to see what I can come up with, might be a good idea 
>to use the same formatting as Andy's test cases anyway.

Let me outline RDQL testing in Jena (for those who haven't experienced its
complete undocumentedness :-).  I'm open to improvements - the design has
been "need driven" so far and so isn't perfect.

My experience has been that detailed testing pays off but the up front cost
is significant.  A plan (design vocabularies) for result set testing should
include encoding result sets themselves.  It is quite a lot of work so
sharing test sets is a real benefit.  I am willing to help out in vocabulary
design and also to contribute the query test harness I have for testing
triple pattern matching which be separated from the rest of Jena into a
separate system.

If you aren't interested in how testing is done in RDQL/Jena stop reading


Testing in Jena is with JUnit and for RDQL there a series of small tests,
each test focusing on just one aspect of the language implementation.  Tests
come in 3 types: 

	internal tests - tests the expression evaluator 
	external tests - tests queries on models
	scripting tests - tests calling RDQL queries from Java

The internal tests are the ones Libby first referred to in:


and are done separately to reduce the combinatorial explosion of trying to
test the expression evaluator from within the query language.  Also, I get
Java to calculate the correct answer so the comparison between the
expression evaluator and the real answer is automatically generated.  By the
time these tests have been run, it should be that the expression evaluator
is OK and the rest of the tests focus on the triple matching.

The external tests are in 


and there is a control file (a manifest) which lists the 

	<query file>  <the data file>  <results file> .

The data file can be null (usually is) and the query names the data file.
And, yes, the parser for the syntax is derived from an N-Triple reader :-)
This manifest could be RDF but isn't for readability and because it is
trivially auto-generated with a Perl script (I like the idea of the "little
languages" approach).  When managing lots of tests, simple readability is
very important, including a compact style that a human can easily spot
irregularities in the contents.

A result files might look like:

# Variables:
?b ?y .
# Data:
?b <anon:cdedfd:eea1faaa34:-8000> ?y "11" .
?b <anon:cdedfd:eea1faaa34:-8000> ?y "12" .
?b <http://never/bag> ?y "21" .
?b <http://never/bag> ?y "22" .

which is one line stating the variables (a check - other more), then one
line per result row of the result table serialized as "var, value, var,
value, ... ."  Values are strings, or URI.  The anon: is a hack so that
which bnode is being talked about can be captured.  This couldn't be encoded
in RDF/XML at the time - could now.  Uses the same parser as the control
file.  This will need to change for datatypes.

The table structure of the results file means it is clear to the tester what
the file contains.  As each one has to be checked visually at least once
when created, this is important.

The JUnit setup reads the manifest and creates one testcase per query test.
Tests are executed by running the query on the data, getting back a result
set and comparing the calculated result set with the results file (there is
a special implementation of QueryResults that builds from a file).  BNode
sharing is correctly accounted for - hence the <anon:...> ids.  The result
set comparison code is intentionally simple - it not only has to work, it
has to be clear it works.  Speed isn't an issue at this point - clearly
correct is.

Result sets are tested for equivalence by:

  for each result row in one set
    find the matching row in the other set
    remove it from expected result

At the end, the expected result set should be empty.

This could be done in RDF - Jeremy's model comparison code does graph
isomorphism so a carefully encoded result set in RDF.  A set of set of
bindings should work, being careful to differentiate between BNodes in the
data model and in the encoded model.  However, it has to be clear the right
results are encoded and RDF isn't particularly good at that - I would choose
careful layout of N3 at this point, where the only issue is that the lines
will be a bit long.

Early versions of the Jena's RDQL didn't do the result set checking - they
just ran through the queries to see if they ran and I (occasionally :-()
eye-balled the results.  Then I decided to set aside the time to do it.  It
was a bit of a slog to write the support code, more so to get the result
files (mechanically generated from a run of the tests but visually checked
to be correct), but it has been really worth it.
Received on Friday, 17 January 2003 05:56:41 GMT

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