Re: [search-ws] CQL Parsing Questions

[Ashley Sanders <a.sanders@manchester.ac.uk>]

Ray Denenberg, Library of Congress wrote:
> Currently:
> search-clause-group     =     search-clause-group    Boolean-modified 
> subquery  |   subquery
> subquery    =      "(" query ")"  /    search-clause
> 
> 
> Why can't these two be replaced by:
> 
> search-clause-group     =
> 
> "("search-clause-group")"  |    search-clause   |  search-clause-group 
> Boolean-modified  search-clause
> 
> Or for better readability:
> 
> search-clause-group     =  quoted-search-clause-group | 
> unquoted-search-clause-group
> quoted-search-clause-group  = "("search-clause-group")"
> unquoted-search-clause-group =  search-clause   |  search-clause-group 
> Boolean-modified  search-clause

I have to say, that I can't easily get my head around that.

A few years ago I wrote a cql parser using an LL parser (Boost.Spirit)
so I had to convert the BNF to a form suitable for Boost.Spirit. I've
just added the following queries to the test cases:

   title=(A or B)
   title=(author=xxx)

Thankfully it rejects them as bad queries. Now, either I based my
parser on an old form of the BNF, or my interpretation of it was
coloured by what I thought was sensible at the time.

Anyway, my grammer, edited to remove all the cruft and make it
a bit more BNF like, has the following constructs:

	comparitorSymbol = "<="| ">=" | "<>" | '='| '<' | '>';

	boolean = "and" | "or" | "not" | "prox"

	modifier = '/' modifierName (comparitorSymbol modifierValue)?;

	comparitor = comparitorSymbol | namedComparitor;

	relation = comparitor modifier*;

	booleanGroup = boolean modifier*;

	searchClause =
	  '(' cqlQuery ')' | (index relation)? searchTerm;

  	scopedClause = searchClause (booleanGroup searchClause)*;

	prefixAssignment = '>' (prefix '=')? uri;

	cqlQuery = prefixAssignment* scopedClause;

The searchClause and scopedClause would seem to be the important
clauses. My reading is that whereever an "=" appears as part of
a relation, it can only be followed by a searchTerm.

Ashley.

> 
> --Ray
> 
> ----- Original Message ----- From: "Ashley Sanders" 
> <a.sanders@manchester.ac.uk>
> To: "Ray Denenberg, Library of Congress" <rden@loc.gov>
> Cc: "Hammond, Tony" <t.hammond@nature.com>; 
> <search-ws@lists.oasis-open.org>
> Sent: Wednesday, September 16, 2009 7:43 AM
> Subject: Re: [search-ws] CQL Parsing Questions
> 
> 
>> Ray Denenberg, Library of Congress wrote:
>>> Tony, addressing your first question:
>>>
>>> From: "Hammond, Tony" <t.hammond@nature.com>
>>>>        title=(author=kernighan)
>>>> is equivalent to
>>>>        author=kernighan
>>>> "
>>>>
>>>> and following up with him he claimed this was cooked into the BNF
>>>
>>> Well first take a look at this thread and see if it helps put this 
>>> into some perspective.
>>> http://listserv.loc.gov/cgi-bin/wa?A2=ind0603&L=srw-ed&D=0&T=0&X=2C676213DF8F2521EB&P=1982 
>>> This is a convoluted mess that is better ignored.  The grammar has a 
>>> hole that lead to nonsensical queries and I think that the consensus 
>>> was that it is harder to fix the grammar than to just say that 
>>> queries like these are nonsensical.
>>
>> One can't feeling that if the grammer allows that, then the grammer is 
>> broken and should be fixed.
>>
>>> The real issue was a query like  "title=(A or B)".    Is it a 
>>> shorthand for - "title=A or title=B".
>>
>> That also looks like an horrendous piece of syntax to me. I can't 
>> think of any other language that allows you to specify queries like 
>> that. Admittedly it is often what people want to do when they first come
>> across boolean statements, but I really don't think we shouldn't let
>> them. Especially if it results in a nonsensical mess like
>> title=(author=xxxx)).
>>
>> Do people feel that cql is intended for users or machines? My feeling
>> is that it should be for machine-to-machine communication and therefore
>> doesn't need any syntactic sugar.
>>
>> Ashley.
>> -- 
>> Ashley Sanders               a.sanders@manchester.ac.uk
>> Copac http://copac.ac.uk A Mimas service funded by JISC
>>
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-- 
Ashley Sanders               a.sanders@manchester.ac.uk
Copac http://copac.ac.uk A Mimas service funded by JISC