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comments on 28 April Working Draft of EARL Schema

From: Diego Berrueta <diego.berrueta@fundacionctic.org>
Date: Mon, 25 May 2009 11:53:40 +0000
To: public-wai-ert@w3.org
Cc: Luis Polo Paredes <Luis.polo@fundacionctic.org>, Carlos Iglesias <carlos.iglesias@fundacionctic.org>
Message-Id: <1243259515.3595.62.camel@localhost>
Dear participants of the ERT WG,

We are pleased to submit some comments to the 28 April draft of the EARL
schema specification. Firstly, a short self-introduction is in order to
avoid confusions. Luis Polo and I work for CTIC, as Carlos Iglesias
does, but in a different department. CarlosI regularly pings us about
the updates on EARL. Moreover, we are the developers of Vapour [1], an
online validation tool which is available at [2]. Vapour internally uses
EARL (and HTTP-in-RDF) to capture the results of its analysis.
Obviously, it also exports the results in EARL (look for the "RDF" link
at the bottom of any Vapour report).

We think EARL is a flexible and very useful piece of work, and we are
willing to see it published as a REC as soon as possible. However, we
think a few changes can significatively improve the specification.
Please read our comments below, and feel free to engage in discussion
about any of them.

Best regards,

[1] http://vapour.sourceforge.net/
[2] http://validator.linkeddata.org/

=======

FOAF
****
 
>From a technical point of view, we are not completely sure whether the
semantics of foaf:Document are a perfect fit in the context of EARL.
Apparently foaf:Document is designed for human-oriented documents, while
validation usually applies to any kind of document (i.e., we believe
that the semantics of foaf:Document is too narrow). Our suggestion is to
contact FOAF editors to clarify the intended meaning of foaf:Document,
to see, for instance, if it is intended to cover the XML representation
of a human-oriented document, which can be two different subjects of
validation.
 
DUBLIN CORE
***********
 
The use of the old dc: namespace is not advised in new applications. We
suggest to use exclusively the dct: namespace, which replaces and
extends the obsolete dc: namespace (see the last paragraph of
http://dublincore.org/documents/dces/ : "Over time, however,
implementers are encouraged to use the semantically more precise
dcterms: properties")
 
CLASS-INSTANCE DUALITY
**********************
 
Section 2.7 defines 5 subclasses of earl:OutcomeValue, and a prototype
instance of each of these subclasses. We have some comments regarding
these subclasses and instances:
 
1) The textual definitions of the instances (e.g., earl:passed) and the
subclasses (e.g., earl:Pass) are identical. Therefore, it follows that
they share the very same conceptual space. Consequently, these singleton
instances are also the only ones possible of their kind, i.e., it is
impossible to conceive an instance of earl:Pass different from
earl:passed.
 
2) The duality introduces unnecessary confusion. For instance, under
which condition two tests have the same outcome value? Intuitively, they
have the same outcome if they have the same value (resource) for their
respective earl:outcome properties (e.g., earl:failed, earl:passed...).
However, under the duality, the values cannot be directly compared, as
they could be two different instances of the same subclass (earl:Fail,
earl:Pass...). This greatly obfuscates any SPARQL query on the report.
 
3) The duality introduces confusion on the use of meta-modelling. For
instance, which one of the following is correct?
 
   a) ex:myTestResult1 earl:outcome earl:passed .
   b) ex:myTestResult2 earl:outcome earl:Pass .
 
   In RDF, there is enough syntactic freedom to use any of these
statements. Unfortunately, this freedom makes it more difficult to
compare the results of two tests, because they do not have the same
ontological status. Moreover, the latter option turns into a problem if
the report is to be interpreted as OWL-DL, because it introduces
meta-modelling.
 
Consequently, our suggestion is to drop the five subclasses.
 
CONFORMING REPORTS
******************
 
We have two comments with respect to the Conforming Reports (Section
4.1):
 
1) From our point of view, it is not clear enough how "SHOULD"
requirements are to be interpreted. Which are the precise conditions
under which a report passes or fails a SHOULD requirement? It seems to
us that these kind of requirements have little use in practice, and
consequently, we suggest to drop them.
 
2) It is not clear whether the conformance requirements must take into
account the RDF(S) semantics. For instance, is the following report
valid wrt requirement 2?
 
    ex:assertion rdf:type ex:MyAssertionClass .
    ex:MyAssertionClass rdfs:subClassOf earl:Assertion .
 
Strictly speaking, there isn't any earl:Assertion in the report.
However, RDF(S) Semantics dictate that the triples above entail
(ex:assertion, rdf:type, earl:Assertion), thus making the requirement
pass.
 
We suggest to explicitly clarify whether the RDF(S) entailment rules
must be applied before checking the conformance rules.
 
RDF REPRESENTATION OF EARL
**************************
 
In the RDF description of the EARL ontology, please consider using OWL
constructors such as owl:Class. Note that it is not our suggestion to
drop the RDF/RDFS constructors (such as rdfs:Class), which should be
preserved. Our suggestion is to add the OWL constructors in addition to
the current ones. Using both sets of constructors is harmless and cheap
(it just adds a few triples), but enables both the OWL-aware and the
RDFS-aware applications (graphical ontology editors, reasoners, etc.) to
seamlessly operate with the EARL ontology.

Additionally, please consider adding a direct link to the RDF
description of the EARL ontology from the HTML document. See for
instance the "(rdf)" links at the top of the FOAF HTML document at
http://xmlns.com/foaf/spec/ .

--
Diego Berrueta
R&D Department  -  CTIC Foundation
E-mail: diego.berrueta@fundacionctic.org
Phone: +34 984 29 12 12
Parque Científico Tecnológico Gijón-Asturias-Spain
www.fundacionctic.org
Received on Monday, 25 May 2009 11:57:34 GMT

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