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[Bug 1384] New: [XQuery] some editorial comments on A.2.1 Terminal Types

From: <bugzilla@wiggum.w3.org>
Date: Wed, 11 May 2005 07:37:39 +0000
To: public-qt-comments@w3.org
Cc:
Message-Id: <E1DVlml-0001L8-0H@wiggum.w3.org>

http://www.w3.org/Bugs/Public/show_bug.cgi?id=1384

           Summary: [XQuery] some editorial comments on A.2.1 Terminal Types
           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.2.1 Terminal Types

[See a later comment for suggested alternate wording that achieves the effect of
this section without defining 'terminal' or making long lists of symbols.]

(intent)
    Is it your intention that the characters of every legal query can be
    partitioned into a sequence of terminals and intervening whitespace?
    If so, you'll need to add the following as terminals:
        Char
        "(#" and "#)" (or else Pragma)
        PITarget

    On the other hand, if it's your intention to only include terminals that
    could be next to ignorable whitespace, then there are a bunch that could be
    removed:
        ":"
        """
        "'"
        "<![CDATA["
        "]]>"
        PredefinedEntityRef
        CharRef
        "</"
        "{{"
        "}}"
         EscapeQuot
         EscapeApos
         S

    Note also that some of the terminals derive forms containing other
    terminals, which could complicate things:
        PredefinedEntityRef -> "lt", "gt", ";"
        CharRef             -> ";"
        Comment             -> CommentContents
        DecimalLiteral      -> Digits, "."
        DoubleLiteral       -> Digits, "."
        StringLiteral       -> '"', "'"
        QName               -> NCName, ":"

'terminal'
    This section waffles between two senses of 'terminal': a symbol in the
    grammar, or a group of characters in a query. (E.g., "The XQuery grammar
    defines 153 terminals." vs. "This query contains 1200 terminals.") Maybe
    nobody will mind.

(In my comments, I will abbreviate "delimiting terminal" and "non-delimiting
terminal" as "DT" and "NDT" respectively.)

"delimit"
    The rest of the spec uses "delimit" to mean "mark the start and end", e.g.:
        -- '(:' and ':)' are comment delimiters,
        -- braces delimit an enclosed expression, and
        -- a string literal can be delimited by apostrophes or quotation marks.
    However, in this section, the intended usage appears to be, for example,
    that in
        x+1
    the plus sign "delimits" x and 1. This is odd. It would be plainer to say
    that it "separates" them.  (Note that in A.2.2.1, the examples use the
    phrase "separated by DTs", not "delimited by DTs".)

    So I'd recommend changing "delimit/delimited" to "separate/separated".
    However, I don't recommend changing "(non-)delimiting terminal" to
    "(non-)separating terminal", as both seem like odd phrasing to me. For
    instance, in
        x+1-y
    it would seem reasonable to say that the 1 separates (or delimits, if you
    must) the plus and minus. So to decree that the plus is "separating"
    whereas the 1 is "non-separating" doesn't make sense.  Instead, I think
    "adjoinable" and "non-adjoinable" might be better, or "punctuation-like"
    and "word-like", or "closed" and "open", or just "class 1" and "class 2".

----

"A DT may delimit adjacent NDTs."
    This is not a definition. The real definition is the list.

(list of DTs)
    Delete initial comma.
    Delete "%%%".
    Maybe change """ to '"'.
    Not sure why you need both Comment *and* "(:" + ":)".
    Put them in ASCII order? Some kind of order would be nice.

    "." and "-" are going to cause problems, given that they're valid
    NCNameChars. E.g., if 'x' and '1' are two NDTs, and '-' is the DT that
    will 'delimit' them, you get x-1, which doesn't work. (It's misrecognized
    as a single NCName.)

    Expressing the problem in a different way: A.2.2.1 says that whitespace is
    only required between two NDTs, but '-' is not an NDT, so whitespace isn't
    required between 'x' and '-'. Which is not what you want.

    On the other hand, you can't make "-" an NDT, because then things like
    100-x and (blah)-1 would become illegal.

"NDTs generally start and end with alphabetic characters or digits."
    This is almost a definition, but the "generally" makes it too vague.
    Again, the real definition is the list.

"Adjacent NDTs must be delimited by a DT."
    This doesn't belong in a definition.

(list of NDTs)
    Change ValidationMode to just "lax", "strict".
    Definitely put them in ASCII order.

----

"delimit adjacent"
    Both "definitions" have a phrase along the lines of:
        "a DT [may/must] delimit adjacent NDTs"
    but this makes no sense -- if the DT is between the NDTs, then the NDTs are
    not adjacent! Presumably you mean something like
        "two NDTs may not be adjacent"
    or
        "two adjacent terminals may not both be NDTs"
    or
        "in every pair of adjacent terminals in a query, at least one of the
        terminals must be a DT"

    However, a reasonable response (to any of these) would be:
        But I have no choice! For instance, in the production for VersionDecl,
        it says right there:
            "xquery" "version" etc.
        So the (NDTs) "xquery" and "version" *have* to be adjacent. I can't just
        grab some DT and stick it between them -- I'd get a syntax error!

    The answer, I assume, would be:
        Ah, but S and Comment are DTs, and you certainly *can* (and in fact,
        must) put either or both of those between the "xquery" and "version".

    This illustrates a couple of problems:
    (1) What you mean here by 'adjacent' may not be what the reader thinks.
    (2) S and Comment are the only DTs that people can actually use to separate
        two NDTs (without changing the structure of the query), and they are
        buried in the list, and not mentioned in the prose.

    It might help solve both of these problems if you moved/recast the content
    of this section into A.2.2 Whitespace Rules. (As far as I can tell, the only
    reason to define these classes of terminals is to be able to define where
    whitespace is allowed, and where required, so the move is appropriate.)
Received on Wednesday, 11 May 2005 07:37:42 UTC

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