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[Bug 1385] New: [XQuery] some editorial comments on A.2.2.1 Default Whitespace Handling

From: <bugzilla@wiggum.w3.org>
Date: Wed, 11 May 2005 07:39:45 +0000
To: public-qt-comments@w3.org
Cc:
Message-Id: <E1DVlon-0001T3-Qf@wiggum.w3.org>

http://www.w3.org/Bugs/Public/show_bug.cgi?id=1385

           Summary: [XQuery] some editorial comments on A.2.2.1 Default
                    Whitespace Handling
           Product: XPath / XQuery / XSLT
           Version: Last Call drafts
          Platform: All
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: XQuery
        AssignedTo: chamberl@almaden.ibm.com
        ReportedBy: jmdyck@ibiblio.org
         QAContact: public-qt-comments@w3.org


A.2.2.1 Default Whitespace Handling

[See a later comment for suggested alternate wording.]

(making it all explicit)
    In http://www.w3.org/2005/04/xquery-issues.html#qt-2004Feb0853-01,
    Steven Buxton suggested "that you give up on implicit whitespace rules
    in the EBNF, and go with totally explicit whitespace in every
    EBNF." Apparently the proposal was accepted. And yet the proposed change
    did not occur. What happened?

"[Definition: Whitespace characters are defined by [http:...#NT-S]"
    Put "characters" in bold, because you're defining "whitespace characters",
    not "whitespace".

    Maybe put it in the singular: "A 'whitespace character' is any of the
    characters referenced in the right-hand-side of [...#NT-S]."

"when these characters occur outside of a StringLiteral.]"
    I think this exception is unnecessary. Consider that there isn't an
    exception for QuotAttrValueContent, DirElemContent, etc.

"Ignorable"
    Change to lower-case "i".

"Unless otherwise specified ..., Ignorable whitespace may occur between
terminals,"
    This is not a definition. The real definition comes later.

    It isn't clear how these two phrases relate. That is, given two adjacent
    terminals, how does one determine whether whitespace may be inserted between
    them, i.e., whether Default or Explicit Whitespace Handling applies?
    For example, in the query
        <a>{ "hello" }{ "world" }</a>
    consider the two terminals '}' and '{' in the middle. They both come from
    (different applications of) the EnclosedExpr production, which is not marked
    with 'ws: explicit', and so is subject to Default Whitespace Handling.
    However, you presumably don't want to suggest that ignorable whitespace can
    be inserted between these two terminals. Instead, what I imagine you have in
    mind is that a pair of successive terminals is governed by their nearest
    common ancestor in the syntax tree. In the above example, that's a
    DirElemConstructor, which symbol/production *is* marked 'ws: explicit', so
    ignorable whitespace cannot be inserted. However, as I say, it isn't clear
    that this is the intent.

"and is not significant to the parse tree"
    Well, that's a bit tricky, since the presence/absence of whitespace can
    certainly be significant to the resulting parse tree ('a-b' vs 'a - b').

"For readability, whitespace may be used..."
    This certainly doesn't belong in a definition.

"All allowable whitespace that is not explicitly specified in the EBNF is
ignorable whitespace, and converse, this term does not apply to whitespace that
is explicitly specified. ]
    Change "converse" to "conversely".
    Delete space before right paren.

    You could simplify it by saying
        "Ignorable whitespace is any allowable whitespace that is not explicitly
        specified in the EBNF."
    (Now that's a definition.)

    However, the phrase "allowable whitespace" is not defined. (In fact, this is
    the only occurrence of the word "allowable" in the whole spec.) You could
    delete it; the "not explicitly specified" phrase is doing the real work.

"Whitespace is allowed before the first terminal and after the last terminal of
an expression module."
    Change "an expression module" to just "a module".

"Whitespace is optional between delimiting terminals."
    Change "optional" to "allowed".

    You missed a case: Whitespace is allowed between a delimiting terminal and
    a non-delimiting terminal (in either order). It would be simpler to just
    say "Whitespace is allowed between any two terminals."

(that whole paragraph)
    This paragraph is backwards. It talks about what you can do with ignorable
    whitespace, then defines it in terms of allowable whitespace, then defines
    where whitespace is allowed. The opposite order seems like it would make
    more sense.

"Comments may also act as 'whitespace' to prevent two adjacent terminals from
being recognized as one."
    This suggests that that's the only context in which comments may act as
    whitespace, which is not what you want.

    Should be mentioned in 2.6?

"foo- foo is a syntax error."
    Change "is" to "results in".

"foo-" would be recognized as a QName.
    Not necessarily. That is, when the parser raises a syntax error, it doesn't
    have to "recognize" anything.

"foo -foo parses the same as foo - foo"
    Don't bring parsing into it if you don't have to. Change "parses the same
    as" to "is syntactically equivalent to".

"The parser would match..."
    These sentences are too implementation-specific.

"also parses the same as"
    Ditto previous substitution.

"When used as an operator after the characters of a name, the "-" must be
separated from the name, e.g. by using whitespace or parentheses."
    This is odd wording. It's as if you're saying (e.g.):
        When your query is
            foo-foo
        your query must be
            foo -foo
        or
            (foo)-foo
    which is self-contradictory.  See next point.

"10div 3 results in a syntax error, since the "10" and the "div" would both be
non-delimiting terminals and must be separated by delimiting terminals in order
to be recognized."
    This is very odd wording.  It's as if the parser must realize that I had
    "10" and "div" in mind as distinct terminals, so that it can apply the
    terminal-separation rules.  The "would be" is a tip-off.  Consider this:
    "dog" and "cat" 'would be' non-delimiting terminals, but that doesn't mean
    that "dogcat" results in a syntax error!

    In order to properly apply terminal-separation rules, you need a context in
    which (e.g.) "10" and "div" *are* terminals, rather than 'would be'
    terminals.  And that context is not the query, or the parser, but the
    derivation tree (or syntax tree). E.g., it's fine to say something like:

        Consider the (abbreviated) syntax tree:

                      Expr
                       |
              MultiplicativeExpr
                       |
              +--------+--------+
              |        |        |
          UnionExpr  "div"  UnionExpr
              |        |        |
        IntegerLiteral |  IntegerLiteral
              |        |        |
              ++      +++       +
              ||      |||       |
              10      div       3

        The symbols IntegerLiteral, "div", and IntergerLiteral are all NDTs,
        so the adjacent pairs must be separated by whitespace in the resulting
        query.
Received on Wednesday, 11 May 2005 07:39:52 UTC

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