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Review of Pierre-Antoine's review of SPARQL 1.1 Graph Store HTTP Protocol

From: Antoine Zimmermann <antoine.zimmermann@insa-lyon.fr>
Date: Tue, 30 Aug 2011 18:15:14 +0200
Message-ID: <4E5D0C92.7090604@insa-lyon.fr>
To: public-rdf-wg <public-rdf-wg@w3.org>
Overall, I agree with the comments. However, the review is written like 
a personal review, not as a group review.
Besides, it would be good to put this review on the wiki. It would make 
minor corrections (typos) easier and would help making it a "community 
review".  I provide detailed comments below.

 > * General remark
 >   Several problems I had in reading this document come from the
 >   notion of identification, and the facts that:
 >   + graph IRIs in a graph store actually do not identify a graph
 >     (imutable abstraction), but rather a "slot" (the term comes from
 >     the SPARQL update document) or an "RDF graph content" in the
 >     terminology introduced by that document.
 >   + several notions of identifications are considered in different
 >     parts of the document without making the distinction explicit,
 >     while those notions do not always match:
 >     1. identification in the graph store
 >     2. identification in the HTTP protocol
 >     3. identification/naming in the RDF semantics
 >   This document only refers to 3. once, and in my opinion should not
 >   (see below my remarks on 4.1).
 >   It refers implicitly to 1. and 2. in many places; sometimes the
 >   distinction between the two is not relevant, sometimes the context
 >   is enough to decide. Sometimes, however, the distinction should me
 >   made explicit, as suggested in my remarks below.

should *be* made

 > * 2. Terminology
 > ** Resource: "a network-accessible data object"
 >    I know this definition comes from [RFC2616], but RDF uses
 >    "Resource" in a much broader sense...
 > ** RDF document: "a serialization of an RDF Graph"
 >    The term "document" usually refers to a mutable, "living" thing,
 >    so a better term should probably be used here. Richard Cyganiak
 >    will make a proposal on behalf of the RDF-WG.

We can directly put the suggested term.

 > ** Graph Store: "managed by one or more sevices [SPARQL-UPDATE]"
 >    the definition seems to contradict the one in [SPARQL-UPDATE]
 >    ("one or more" v.s. "a single") but still references it. Strange...
 > ** RDF graph content
 >    the definition is strange: "an information identified by the URI
 >    of named graph"; then it should be named graph ?!...

A named graph is a pair <name,graph>, while the information "identified" 
by the IRI is a single thing.

Moreover, "an information identified" should be replaced by "an 
information resource identified".

 >    besides, what does "identified by an indirect *operation*" mean ?
 >    a better idea seems to define RDF graph contents as the
 >    components" of a graph store (or "slots", as the SPARQL UPDATE
 >    document calls them?)
 > * 4.1. Direct Graph Identification
 >   This section is a bit disturbing...
 >   In the first paragraph, "resource" and "graph" seem to be used as
 >   synonyms without it being explicit.
 >   In the third pargtaph, "... the most common usage of a Resource-URI
 >   is to identify a resource". Is there *any* other usage??

third *paragraph*

 >   Then we read in the next paragraph that "we are not directly
 >   identifying an RDF graph". Why then is the section entitled "Direct
 >   Graph Identification"? The problem here is again about what Graph
 >   IRIs really identify.
 >   Then we read: "Intuitively, the set of interpetations that satisfy
 >   [RDF-MT] the RDF graph that the RDF document is a serialization of
 >   can be thought of as this RDF graph content." It is really not
 >   "intuitive" for me that a set of interpretations can be thought of
 >   as an RDF graph content (an information resource). This sentence
 >   tends to muddy the waters about the definition of RDF graph content.

the set of *interpretations*

 >   I would rather say that the RDF graph is the current *state* of the
 >   RDF graph content (see g-box and g-snap in
 >   http://www.w3.org/2011/rdf-wg/wiki/Graph_Terminology).

I'm not sure if I agree but this just show that the notion of RDF graph 
content is not clear enough.

 >   This remark also applies to Figure 1.
 > * 5.2 HTTP PUT
 >  + "[the URI] identifies the RDF payload". The RDF payload is an
 >    entity, not a a resource; it is *not* identified by a URI.

"not a a resource"

I do not understand what you mean. "entity", "resource", what are these 
things? Do you mean RDF Resource? "Resource" as in REST? Everything can 
be identified by a URI and everything is an RDF Resource.

 >  + In section 5.2. HTTP PUT, it is not clear whether the service is
 >    allowed to alter the RDF payload before storing it, which is
 >    common practice in the REST world.
 > * 5.3 HTTP DELETE "overriden"
 >   The term "overridden" is used twice but never defined. It is not
 >   clear from the context what it means exactly.
 > * 5.5.1 Ambiguity Regarding the Range of HTTP GET
 >  I find this section a little confusing; if I get it right, I would
 >  suggest to keep the first half of the first paragraph
 >  ("Historically"..."the response code returned.") followed something
 >  like:

followed *by* something

 >    This protocols suggests that graph IRIs that are under the control
 >    of the service owner return a status code 200 OK, with an RDF
 >    payload serializing the RDF graph content identified by that graph
 >    IRI in the graph store. This amounts to aligning the
 >    identification relation (between the graph IRI and the graph
 >    content resource) in the graph store to the identification
 >    relation in the HTTP protocol, and this is consistent with the
 >    recommendations in [WEBARCH] as RDF graph contents are indeed
 >    information resources.
 >    This protocols also propose, in section 4.2, a way to build a

This protocol also proposes

 >    dereferenceable URI from any graph IRI in the graph store, even
 >    those not under the control of the service owner or those that can
 >    not be made dereferenceable. Those new dereferenceable URIs can
 >    therefore be considered to identify, in the HTTP protocol, the
 >    corresponding RDF graph content in the graph store. In that case,
 >    the identification relation in the graph store is different from
 >    the identification relation in the HTTP protocol.
 > * Typos and other minor comments
 >  + Last paragraph of section 2 has two main verbs in a single
 >    sentence.

and the sentence says "MUST interpet" (sic)

 >  + Parenthesis in the 1st paragraph of section 4.1 is grammatically
 >    inconsistent with the text ("by")
 >  + Figures can not be understood when printed in b&w, which is not
 >    good
 >  + Paragraph just before 5.5.1 is missing a word between "a" and
 >    "SHOULD"
 >  + Secrion 5.5.1 : recieve ? receive

*Section* 5.5.1

 >  + Section 5.6 seems to be redundant with the HTTP RFC. If so, it
 >    should clearly refer to the RFC and be marked as informative, as
 >    it does not define anything new.
 >  + Section 5.7: a graph content can not be used as an RDF payload, as
 >    it is not an RDF *document*.
 >  + Section 5.7: a SPARQL UPDATE query can not be used as an RDF
 >    payload, as it is not RDF.

Antoine Zimmermann
Researcher at:
Laboratoire d'InfoRmatique en Image et Systèmes d'information
Database Group
7 Avenue Jean Capelle
69621 Villeurbanne Cedex
Tel: +33(0)4 72 43 61 74 - Fax: +33(0)4 72 43 87 13
Lecturer at:
Institut National des Sciences Appliquées de Lyon
20 Avenue Albert Einstein
69621 Villeurbanne Cedex
Received on Tuesday, 30 August 2011 16:15:45 GMT

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