Re: BNF for SQL LIKE Predicate

[Farrukh Najmi <Farrukh.Najmi@Sun.COM>]

Len,

I agree with your proposed text. I feel it should be placed in the appendix of
RS and referenced from main text.

BTW we know of at least one XML Vendor XML Global that feels quite comfortable
with this idea. See:

http://lists.oasis-open.org/archives/regrep-query/200109/msg00003.html
(Matt's agreement)
http://lists.oasis-open.org/archives/regrep-query/200109/msg00001.html
(David's agreement)



Len Gallagher wrote:

> Query team,
>
> During last Friday's teleconference I expressed some concern about ad hoc
> adoption of SQL LIKE predicate syntax in our "Clause" element for Registry
> Query. The reason for my reluctance is the complexity of SQL LIKE. I'm
> convinced that XML vendors will not be willing to implement it
> completely.  The trick is then to agree on some reasonable subset.
>
> Attached is a file called "LIKEpredicate.txt" that is copied from the BNF
> for the SQL <like predicate> as specified in ISO/IEC 9075-2:1999.  It is
> very complex because it takes full advantage of the power of SQL and allows
> character expressions, character functions, and numeric functions in its
> specification.
>
> If we decide to go this route -- and I'm still not convinced that a
> majority of the vendors (or Registry clients) will want to do that -- then
> we need to agree on some restrictions. Here are some suggestions:
>
> 1) The SQL LIKE predicate for Registry Query shall be a <character like
> predicate>.
>
> 2) The <character match value> in a <character like predicate> shall be a
> <column reference> that is a single <column name> that matches a visible
> attribute name of the relevant Registry Query class. The underlying data
> type of this attribute shall be "String".
>
> 3) The <character pattern> in a <character like predicate> shall be a
> <character string literal> that does not contain a <character set
> specification> or a <character representation>.
>
> 4) The <escape character> in a <character like predicate> shall be a
> <character string literal> that does not contain a <character set
> specification> or a <character representation>.
>
> With these restrictions, the SQL LIKE predicate for Registry Query could be
> reduced to the following BNF representation:
>
> <character like predicate> ::=
>     <column name> [ NOT ] LIKE <character pattern>
>     [ ESCAPE <escape character> ]
>
> <character pattern> ::= <character string literal>
>
> <escape character> ::= <character string literal>
>
> <character string literal> ::= <quote> [ <character representation>... ]
> <quote>
>
> <character representation> ::= <nonquote character> | <quote symbol>
>
> <nonquote character> ::=  -- Any character from the default character set
> that is not a single quote character, i.e. not the ' character.
>
> <quote symbol> ::= <quote><quote>
>
> But this still leaves the very comprehensive rules for how to specify and
> implement the <character pattern> and <escape character> -- but these rules
> are fully specified in the SQL standard and we could simply point to them.
>
> Regards,
> Len
>
> **************************************************************
> Len Gallagher                             LGallagher@nist.gov
> NIST                                      Work: 301-975-3251
> Bldg 820  Room 562                        Home: 301-424-1928
> Gaithersburg, MD 20899-8970 USA           Fax: 301-948-6213
> **************************************************************
>
>   ------------------------------------------------------------------------
>
>    LIKEpredicate.txtName: LIKEpredicate.txt
>                     Type: Plain Text (text/plain)

--
Regards,
Farrukh

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