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Another suggestion for the BNF

  • Subject: Another suggestion for the BNF
  • From: James Hester <jrh@xxxxxxxxxxxx>
  • Date: Mon, 1 Jul 2002 05:00:17 +0100 (BST)
Hello again,

Ralf and I have detected what appears to be another problem with the
BNF, this time in regard to embedded quotes.   Consider the following
bit of text:

data_1A4U
#
_site.id _site.details
'ND'' 'NAD/NADP SELECTIVITY AMINO ACID.'
#

Now consider the BNF definitions:
<data_value_2>  ::= <S_quote> <S_quote_string> <S_quote> 

<S_quote_string> ::= { <S_quote> <non_blank_char> | <not_a_S_quote>} *

a S_quote_string is thus

<S_quote> { <S_quote> <non_blank_char> | <not_a_S_quote> } * <S_quote>

Now, the problem is that, because <non_blank_char> includes a <S_quote>
(as it must for double single quotes inside the string), a double final
S_quote as in the above example is matched by the
<S_quote><non_blank_char> sequence, leaving nothing for the final
<S_quote> and meaning that the two data items above are parsed as a
single data item.

One idea for a fix:

<S_quote_string> ::=
  { <S_quote> <non_blank_char> | <not_a_S_quote>} * <S_quote> *

making the specification for the whole S_squote delimited text 
<S_quote> { <S_quote> <non_blank_char> | <not_a_S_quote>} * <S_quote>+

James Hester.
-- 
_______________________________________________________________________
James Hester, ANBF                             KEK
e-mail: jrh@anbf2.kek.jp                       Oho 1-1
Phone: +81 298 64 7959                         Tsukuba, Ibaraki 305
  Fax: +81 298 64 7967                         Japan
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