W3C home > Mailing lists > Public > public-rdf-dawg@w3.org > October to December 2009

Review of SPARQL 1.1

From: Birte Glimm <birte.glimm@comlab.ox.ac.uk>
Date: Fri, 2 Oct 2009 22:01:27 +0100
Message-ID: <492f2b0b0910021401p1c6cc487o6d4773544dc634af@mail.gmail.com>
To: SPARQL Working Group <public-rdf-dawg@w3.org>
Hi all, Andy, Steve,
here is my review for the FPWD of SPARQL 1.1. I'll not be able to
attend the telecon on Tuesday since I'll be travelling, but I hope we
can sort out all questions before.
Birte


I am not sure what will happen with all the @@ comments, some might
stay, but will, for example, the Abstract be rewritten before FPWD or
will it just be annotated with @@ Old intro - rewrite?

I understand that the doc will eventually b merged with the SPARQL 1.0
doc, but in several places you rely on definitions from Sec 12 of
SPARQL 1.0. If after the merge your sections will be before Sec 12,
you will have lots of forward references. Another way of merging would
be to have all the examples in an earlier section and put the
definitions into the section that is now Sec 12 of SPARQL 1.0. This
would then follow the way that the SPARQL 1.0 doc is organised (all
features introduced by motivation and examples and one section with
fomal definitions). This is just something to keep in mind for the
doc.

In general, I would prefer to see some introductory sentence at the
beginning of the sections. In Sec 2 (and others), for example, you
directly start with an example without saying anything of what
aggregate functions are, what the example will demonstrate, etc. One
can just guess from the section heading that the example will
demonstrate how aggregate functions work.

I woud also prefer if each grammar bit is preceeded with a short
explanation of which parts of the grammar are new, which ones extend
previous definitions and which ones replace previous definitions.

Intro, 1st par: ... the backgraound to *the* choice

Sec 2:
Add headings Data:, Query:, and Query Result/Resuts: to the example to
be consistent with the rest of SPARQL 1.0 and 1.1.
The @@ comment for ProjectValues refers to the Project rule, but that
is only introduced later in the doc and is not from SPARQL 1.0, please
add a link.
Algebra Operators:
I suggest a complete sentence at the beginning, e.g.:
The operators that make up aggregates consist of three functions: Key,
Partition, and Aggregations.
and then continue to define the three. Since the definitions are quite
long, it is otherwise hard not to loose the context.
Key is lowercase, but partition and aggregation are uppercase.
I would also prefer complete sentences above the definitions, e.g.,
Key *is* as function...
I do understand what you mean by single-valued? Is it injective (a
unique argument produces a unique result)? I don't think it is. Is the
result always a singleton set? Also not really I think.
Further, I think varlist in partition is not the same as varlist in
key and I would prefer to name them something like namedVars and
groupVars because for key it refers to the named variables from the
select part of a query and for partition it refers to the named
variables from the group by part of the query. I do not understand the
def of partition and I am not sure whether or not you would need both
var lists in partition. Here is my understanding of partition by means
of an example (about books and their avarage price per publisher):
Data:
:a :publishes :a1 .
:a :publishes :a2 .
:b :publishes :b1 .
:a1 :costs 12 .
:a2 :costs 20 .
:b1 :costs 4 .
Query:
SELECT ?p, AVG(?price) AS avg WHERE { ?p :publishes ?book . ?book
:costs ?price . } GROUP BY ?p
Result:
p/:a, avg/16
p/:b, avg/4
Now I have solution mappings
m1={ ?p/:a, ?book/:a1, ?price/12 }
m2={ ?p/:a, ?book/:a2, ?price/20 }
m3={ ?p/:b, ?book/:b1, ?price/4 }
and omega = { m1, m2, m3 }
I expect a partition
{ {m1, m2}, {m3} } or if you want to project out variables there already
{ { key(namedVars, m1), key(namedVars, m2) }, { key(namedVars, m3) } }
For the first, I would define partition as follows:
partition(groupVars, omega)={ { m_1, ..., m_n } | m_1, ..., m_n in
omega and key(groupVars, m_1) = ... = key(groupVars, m_n) }
for the latter
partition(groupVars, namedVars, omega)={ { key(namedVars, m_1), ...,
key(namedVars, m_n) } | m_1, ..., m_n in omega and key(groupVars, m_1)
= ... = key(groupVars, m_n) }
I don't think you want the later though because you still need the
whole solution mapping to compute the average.
I am not sure why you keep omega as part of the mappings in a
partition and in the definition of aggregation it seems that partition
returns a different omega then what it got as input, but this is not
clear from the definition of partition. Maybe that is because you
write omega in omega and that should be something else?
For the aggregation, it remained completely unclear why it is defined
as it is and how it is supposed to work. I would assume that I have in
the example, AVG as agg, and I would need the partioning and then I
compute a mapping that contains the aggregated values?

What does AST stand for in the section headings (Mapping from AST to
Algebra)? Later in Sec 3 it says ASP. Is that intended?
Below the example just before section 3, you use BGP(triple pattern).
That is not really defined neither in SPARQL 1.0 nor here. SPARQL 1.0
mentions that briefly in 12.2.1, but I suggest a more precise
definition somewhere.

Will the wiki references stay in the doc? If so, I suggest to give
them a heading such as "Further Material", "Relevant Links/Material".

Sec 3: Add "Query:" above the query in line with the SPARQL 1.0 doc.

Will the comments such as -- Andy at the top of Sec 4 stay?

Sec 4, 1st par: It *it* does

Sec 4, 2nd par: ...a fil*t*er expression

Sec 4, Syntax, text below grammar rules for FILTER: ... and
NotExistsPattern *s*but ...
following note: equivalence to -> equivalent to

I would prefer complete sentences, e.g., "To facilitate this, "
followed by a definition with a border around it looks awkward.
Similarly in the paragraph below the definition the last sentence is
just: See below. I would delete that.

I would not say "We define:" in the definition because it has already
the heading "Definition: term to be defined"

The subsection "Mapping from AST to Algebra" in Sec 4 starts directly
with some data, no introductory sentence and after the data part of a
sentence starts in lowercase "becomes a filter..." Also, in the given
data, are <t> and <p> supposed to be a full URIs/IRIs? Is <p> the same
as :p? The forms <p>, <t> are not used anywhere in SPARQL 1.0 other
when t or are fullly qualified IRIs.

The section needs more explanation.

Sec 5, Definition Extend: an RD*F* *T*erm. Again, I would prefr not to
say "We define " in the definition.
Note below syn*ta*ctic
Received on Friday, 2 October 2009 21:02:00 GMT

This archive was generated by hypermail 2.3.1 : Tuesday, 26 March 2013 16:15:40 GMT