- From: Souri Das <Souripriya.Das@oracle.com>
- Date: Tue, 05 Jan 2010 12:58:28 -0500
- To: Andy Seaborne <andy.seaborne@talis.com>
- CC: public-rdf-dawg@w3.org
- Message-ID: <4B437DC4.30107@Oracle.com>
Andy, > One more question: Are we always requiring an alias for an expression? > That is, would SELECT SUM(?lprice) ... (i.e., without the alias > ?totalPrice) be allowed? /Not formally decided (I couldn't find a resolution anyway) but there is a body of support for requiring the alias name. If sent over HTP with the results format, a name is required. Just for query, a processor can easily generate one at parse time so there is no requirement for it. Your opinion? Personally, I think the work to generate a safe one (it's similar to calculating SELECT *) is negligible and so a design to the benefit of the user is to be preferred. Andy / My opinion would be to require an alias name, mainly because of the following: * Specifying a binding for an alias variable works uniformly for everything: 1) in Results XML format 2) as an "output" variable of a subquery that can be referenced in outer query, and 3) in a top-level query. * Although it does put a burden on the user to come up with the name of a variable that is not potentially bound, it makes the query appear much clearer. Thanks, - Souri. Andy Seaborne wrote: > > > On 05/01/2010 2:33 PM, Souripriya Das wrote: >> Andy and Steve, >> >> Thanks for looking at the comments on such a short notice. >> >> You can ignore my comment about 8.1 (Negation Syntax). It was more of a >> minor pretty-printing nit-picking. But, now I see that it is consistent >> with the way the grammar is specified. (Regarding WS, I am assuming that >> whitespaces are allowed between the (NOT) EXISTS and the >> GroupGraphPattern.) > > Yes. white space (or none) is allowed in the draft grammar. > >> Regarding my comments about "value of expression in presence of operands >> of incorrect data types" ("semantics unclear" in Sec 2.5, Sec 13.1.2, >> and Sec 9): The idea of skipping the binding (effectively binding=null?) >> sounds good. >> >> For the query example in Sec 9, I still think it will nicely show the >> grouping aspect if we extend the SELECT list slightly to SELECT ?org >> (SUM(?lprice) AS ?totalPrice). > > [Steve] > > >> One more question: Are we always requiring an alias for an expression? >> That is, would SELECT SUM(?lprice) ... (i.e., without the alias >> ?totalPrice) be allowed? > > Not formally decided (I couldn't find a resolution anyway) but there > is a body of support for requiring the alias name. If sent over HTP > with the results format, a name is required. Just for query, a > processor can easily generate one at parse time so there is no > requirement for it. > > Your opinion? > > Personally, I think the work to generate a safe one (it's similar to > calculating SELECT *) is negligible and so a design to the benefit of > the user is to be preferred. > > Andy > >> >> Thanks, >> >> - Souri. >> >> >> ----- Original Message ----- >> From: andy.seaborne@talis.com >> To: SOURIPRIYA.DAS@oracle.com >> Cc: public-rdf-dawg@w3.org >> Sent: Tuesday, January 5, 2010 8:40:38 AM GMT -05:00 US/Canada Eastern >> Subject: Re: SPARQL Query 1.1 review comments >> >> Souri- thank you for you comments which are addressed below toegther >> with Steve's earlier mesaage. >> >> On 05/01/2010 5:19 AM, Souripriya Das wrote: >> >> Here are my (slightly rushed :-)) review comments: >> >> * [Section 2.5: Creating Values with Expressions] >> o [semantics unclear] If a solution for a query with >> "SELECT ?x ?y ..." would include bindings >> ?x="10"^^xsd:integer and ?y="Hello", then what would >> happen to that solution for "SELECT ?x+?y ..."? >> + Would that solution be skipped (i.e., Is there an >> implicit directive that a solution is returned >> only if all the SELECT-list expressions can be >> evaluated without error?)? >> + The solution would be returned, but the value of >> the expression will show up as error. >> >> >> There are three design possibilities - whole results are an error, skip >> the row or skip just the binding. Binding an error token is strange >> (typing; and also whether it itself can occur RDF). I think that causing >> everythign to be an error is bad because it does not scale and is at >> odds with the SPARQL design. >> >> The design I have in mind skips just the binding. The extend operator >> works on one binding, not an entire row. I have fixed the definition (it >> had an "and" where it needed "or"). >> >> extend(μ, var, expr) = μ if var not in dom(μ) *or* eval(expr) is an >> error >> >> o [would like to know] Are we allowing expressions for >> CONSTRUCT as well? >> >> >> There are no plans for that - it can be done with sub-SELECT. >> >> * [Section 3: RDF Term Constraints (Informative)] >> o [typo] Subsections for Section 3 show only "3.1 Other >> Term Constraints" in the content, but there are two >> other subsections: "3.1 Restricting the Value of >> Strings" and "3.2 Restricting Numeric Values". >> >> >> The XML was malformed for the xmlspec.xsl script. Fixed. >> >> * [Section 13.1.2: "SELECT expressions"] >> o [typo] change: SELCT => SELECT >> >> Done >> >> o [semantics unclear] What is the value of an expression >> if any of the operands of an operator does not have the >> proper data type? Do we ignore (i.e., not return) the >> corresponding solution? Or, do we return a >> pre-designated RDF error term in place of the value of >> that expression? >> + For example, if the RDF data shown is altered to >> replace: the triple, :*book1 ns:price 42*, with >> *:book1 ns:price "priceless*", then what will be >> the results for the two queries? >> >> >> See sec 2.5. comment above. >> >> * [Section 9: Aggregate Functions] >> o [semantics unclear] Somewhat similar question as in the >> case of SELECT expressions: How to evaluate an >> expression, in this case aggregate functions, in >> presence of values of different types? For example, what >> would be ?totalPrice if instead of *:book3 :price 7, *we >> had :*book3 :price "priceless*"? >> o [enhance the query] In the query example, could we >> extend the SELECT list from SELECT (SUM(?lprice) AS >> ?totalPrice) to, say, SELECT ?org (SUM(?lprice) AS >> ?totalPrice), or further extend to SELECT ?org >> COUNT(DISTINCT ?author) (SUM(?lprice) AS ?totalPrice)? >> Just selecting SUM(?lprice) is not very interesting. >> * [Section 10: Subqueries] >> o [fix the query] The query does not seem right. >> Specifically, the outer SELECT list cannot include ?name >> which is not exposed by (that is, not in the SELECT list >> of) the subquery. [Also, a minor typo: has an extra >> '}'.] One possible way to fix it would be: >> >> PREFIX : <http://people.example/> >> PREFIX : <http://people.example/> >> SELECT ?y *?minName* >> WHERE { >> :alice :knows ?y . >> { >> SELECT ?y (MIN(?name) *AS ?minName*) >> WHERE { >> ?y :name ?name . >> } GROUP BY ?y >> } >> } >> >> o [more details needed] May need more details about the >> scope of variables mentioned in the subquery. >> * [Section 8.1: Negation Syntax] >> o [typo] We need to put a blank space between 'EXISTS' (or >> 'NOT EXISTS') and GroupGraphPattern >> >> I don't understand this comment. Exactly which point in the doc are you >> referring to? >> >> Or do you mean the grammar needs to specify a space is needed between >> EXISTS and GrroupGraphPattern (it's not - covered by the WS rules of the >> grammar). >> >> >> Andy >> >> ______________________________________________________________________ >> This email has been scanned by the MessageLabs Email Security System. >> For more information please visit http://www.messagelabs.com/email >> ______________________________________________________________________
Received on Tuesday, 5 January 2010 18:00:28 UTC