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RE: SPARQL / Language spec ready for review [Howard's feedback]

From: Howard Katz <howardk@fatdog.com>
Date: Tue, 5 Oct 2004 07:12:27 -0700
To: "Eric Prud'hommeaux" <eric@w3.org>, "Dave Beckett" <dave.beckett@bristol.ac.uk>
Cc: "Dan Connolly" <connolly@w3.org>, "Andy Seaborne" <andy.seaborne@hp.com>, "Steve Harris" <S.W.Harris@ecs.soton.ac.uk>, "RDF Data Access Working Group" <public-rdf-dawg@w3.org>
Message-ID: <IKEOLCDFPBBPPAHGNKKOGEPBEPAA.howardk@fatdog.com>

Hi Eric,

This is done off a fairly quick read. I haven't tried to correlate my
feedback against Dave's or anyone else's comments. I'm mostly *not* doing a
lot of nit-picking against spelling errors and other typos at this point,
ie, this is a bit of a higher-level view. This was reviewed against 1.82.

Hope it's useful,
Howard

------------------------
1 Introduction

If you're having sub-headings, as in "Document Outline" and "Document
Conventions", wouldn't it be more consistent to sub-number them, as in "1.1"
and "1.2"?

---------------------
2 Making Simple Queries

Why not use the same data and query example(s) in the initial pictorial
section and the following SPARQL syntax section? That way readers would get
a better feel for how one form translates into the other.

-----------------------
last paragraph

Where doesn't the "andy" come from? I don't see him in the graph above.

------------------------
2.1 Writing a Simple Query

Second paragraph, "The terms quoted ..."

It's a fair distance from this sentence to the actual example below, and the
reader's eyes have to jump down to the example and then find their way all
the way back up again. Why not move this paragraph to either after the
"Data:" section or after the "Query:" section?

----------------------
2.2 Triple Patterns

I'm not sure if this requires a bit of reorg or not, but all the examples in
the preceding section have WHERE clauses containing triple patterns, but you
don't introduce the concept until here.

More importantly, you never say what a triple pattern IS (ie, something
along the lines of "A template for describing an s-p-o triple, with
variables representing missing information to be filled in by the query" or
some such. That would be very useful for reader.

At a minimum, I'd change sentence one from
"The building blocks of queries are triple patterns"
to
"The building blocks of queries are triple patterns, shown as the arguments
of the WHERE clauses in the three queries in the preceding section."

---------------------
As well, a brief sentence explaining that triple patterns are delimited by
parentheses ("(" and ")") would be useful.

--------------------
Paragraph 2, "A triple pattern has either a graph label (URIRef, literal) or
a named variable in each of the subject, predicate and object positions."
Literals of course can only go in the object position. Is it ok to be this
imprecise? (I'm asking because I don't know and don't have a strong
opinion.)

----------------------
Definition: Triple Pattern
      "3" -> "three"

----------------------
2.3 Graph Patterns
First paragraph, "This starts with conjunction - the 'and' of triple
patterns."

It's not clear what "This ..." refers to. How about something like, "We'll
first look at conjunctions, which combine triple patterns using "and".

-----------------------
Paragraph starting "There are is a bNode ..."

1) "are is" -> "is"

2) I don't understand the final clause in second sentence: ", nor to any
query."

------------------------
2.4 Multiple Matches

"The results of query" -> "The results of a query"

------------------------
4.2 Multiple Optional Blocks

Second paragraph, you introduce the concept of outer block. This hasn't been
previously discussed, so it's unclear what this refers to. Please define. As
well, you follow with a hypothetical, "If a new variable is introduced in an
optional block ...", a short "WHERE" snippet example showing this would be
very helpful.

------------------------
4.3 Optional Matching

Is there a new syntactic feature introduced here? If so, an example would be
helpful.
------------------------
5 Nested Patterns

It would be useful to introduce this section with a brief explanation of
what nesting is. Ie, What is its purpose? Why is it useful?

------------------------
Final example in section:

I don't see a correspondance between the arguments of the SELECT statement
and the headings in the result table. "mbox" would have to be SELECTed to be
output, wouldn't it, and what happened to "name"?

------------------------
8 Choosing What to Query

Third paragraph, "To execute a query, there needs to be the query and an RDF
graph."
Awkward. How about: "Query execution requires both a query and an RDF
graph."

-------------------------
9 Querying the Origin of Statements

I realize you have a footnote on the first sentence saying the semantics are
undefined, but how about at least a very loose explanation of what a SOURCE
is in the paragraph itself, so the reader at least has a rough idea of
you're talking about? Maybe the footnote could be reworked and moved into
sentence number two? Ie, something like (I'm not claiming this is
technically accurate):

" ... many RDF data stores augment this with the source of each statement.
Source is at present undefined, but is expected to refer in some
implementation-dependent way to the document of origin, possibly given by a
URL."

or some such.

------------------------
10 Summary of Query Patterns

Does the bullet "disjunction" correspond to the "alternatives" mentioned in
"6 More Pattern Matching - Alternatives"?  I don't know the ultimate
dispostion of this section but suggest if it stays and is mentioned in this
list, that the terminology be made consistent.

------------------------
11.2 Constructing an Output Graph

I'm confused by the three boxed snippets. #3 is labelled "Example" -- are
the first two NOT examples as well? What distinguishes #3 from #1 and #2?

Also, #3 has "PREFIX . . . CONSTRUCT". Are the ellipses part of the syntax??

--------------------------
11.4 Asking "yes" or "no" questions
   -> 11.4 Asking "Yes" or "No" Questions

I'd also invert sentence #1 and tighten a bit:
"In order just to test whether a query pattern has a query solution or not,
the application can use the ASK form."
   ->
"Applications can use the ASK form to test whether a query pattern has a
solution or not."

------------------------------
12.1 Standard Operations

"The SPARQL language provides some of the operations on plain literals, XSD
integers and XSD floats taken from those in XQuery and XPath Functions and
Operators <http://www.w3.org/TR/xpath-functions/>."

A bit awkward. Do you mean:

"The SPARQL language provides a subset of the operations on plain literals,
XSD integers and XSD floats defined in XQuery and XPath Functions and
Operators <http://www.w3.org/TR/xpath-functions/>."
Received on Tuesday, 5 October 2004 14:10:47 GMT

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