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Understanding @keywords

From: Sean B. Palmer <sean@mysterylights.com>
Date: Thu, 26 Feb 2004 17:22:21 +0000
Message-ID: <403E2B4D.3010806@mysterylights.com>
To: public-cwm-talk@w3.org

[I've been working on a set of explanatory @keywords examples to
better understand how it's implemented. Please consider adding
some of these tests to the CWM regression suite.]

@keywords allows one to carve out the set of reserved names which
CWM is to use. Any that CWM does not recognize natively will be
output as literals:

$ echo '@keywords p, q, r . p q r .' | \
    cwm | egrep -v '^[ \t]*#|^[ \t]*$'

     "p"     "q" "r" .

Special keywords that CWM does recognize natively will be output
as their normal selves, which usually means retaining the keyword:

$ echo '@keywords a, Doc . <> a Doc .' | \
    cwm | egrep -v '^[ \t]*#|^[ \t]*$'

     <>     a "Doc" .

(Using "this" causes an error; a seperate bug report is archived at
http://lists.w3.org/Archives/Public/public-cwm-bugs/2004Feb/0003).
Once keywords have been declared, any bare (non-colon-prefixed) words
that are used are put into the default prefix space if it has been
delcared:

$ echo '@keywords . @prefix : <#> . Mydoc a :Doc .' | \
    cwm | egrep -v '^[ \t]*#|^[ \t]*$'

      @prefix : <#> .
     :Mydoc     :a :Doc .

Note that "a" does not remain as an rdf:type synonym since it hasn't
been declared as a keyword. If you try to use the default prefixing
mechanism without using @prefix, an error will be raised:

$ echo '@keywords . p a q .' | \
    cwm | egrep -v '^[ \t]*#|^[ \t]*$'

    notation3.BadSyntax: Line 1 of <file:.../keyword-test/>:
      Bad syntax (Prefix  not bound) at ^ in:
      "@keywords . ^p a q ."

The is and of keywords are not retained as special keywords outside
of their valid context, and are converted into literals (or URIs if
the default prefix space is declared) elsewhere:

$ echo '@keywords is, a, of . is a of .' | \
    cwm | egrep -v '^[ \t]*#|^[ \t]*$'

     "is"     a "of" .

Note also that they can be used both inside and outside of their
special contexts and will be converted or recognized accordingly:

$ echo '@keywords is, a, of . is is a of of .' | \
    cwm | egrep -v '^[ \t]*#|^[ \t]*$'

     "of"     "a" "is" .

In the example above, "a" is not retained in its meaning of rdf:type,
but this is a quirk of the is/of idiom, which does not allow that
special meaning, as illustrated here:

$ echo '@prefix : <#> . :is is a of :of .' | \
    cwm | egrep -v '^[ \t]*#|^[ \t]*$'

    notation3.BadSyntax: Line 1 of <file:.../keyword-test/>:
      Bad syntax (expected <property> after 'is') at ^ in:
      "@prefix : <#> . :is is^ a of :of ."

Keywords must be declared before they are used, otherwise a "bad
syntax" error will be given:

$ echo 'p q r. @keywords p, q, r .' | \
    cwm | egrep -v '^[ \t]*#|^[ \t]*$'

    notation3.BadSyntax: Line 1 of <file:.../keyword-test/>:
      Bad syntax (expected directive or statement) at ^ in:
      "^p q r. @keywords p, q, r ."

Likewise, builtin keywords can be used before they are overriden:

$ echo '<> a <#Doc> . @keywords .' | \
    cwm | egrep -v '^[ \t]*#|^[ \t]*$'

      @prefix : <#> .
     <>     a :Doc .

Subsequent keyword declarations appear to overwrite all of the keywords
delcared earlier on; they do not get appended to the keyword space:

$ echo '@keywords p, q, r . p q r . @keywords s . p q r .' | \
    cwm | egrep -v '^[ \t]*#|^[ \t]*$'

    notation3.BadSyntax: Line 1 of <file:.../keyword-test/>:
      Bad syntax (Prefix  not bound) at ^ in:
      "@keywords p, q, r . p q r . @keywords s . ^p q r ."

The default prefixes even work nicely in @forAll declarations:

$ echo '@keywords . @prefix : <#> . @forAll p .' | \
    cwm | egrep -v '^[ \t]*#|^[ \t]*$'

     this     <http://www.w3.org/2000/10/swap/log#forAll> <#p> .

Keywords must be "words"; they cannot contain special characters:

$ echo '@keywords = .' | cwm | egrep -v '^[ \t]*#|^[ \t]*$'

    notation3.BadSyntax: Line 1 of <file:.../keyword-test/>:
      Bad syntax ('@keywords' needs comma separated list of words)
      at ^ in: "@keywords = .^"

Declaring "@keywords prefix, keywords." is likely to cause some very
strange bugs at the moment. (A bug report has been sent and archived
at http://lists.w3.org/Archives/Public/public-cwm-bugs/2004Feb/0005).

Keywords can be delcared in formulae, and persist outside of the
formulae as expected:

$ echo '@prefix : <#> . { @keywords p, q . p q r } => { r p q } . \
    p r t .' | cwm | egrep -v '^[ \t]*#|^[ \t]*$'

      @prefix : <#> .
     "p"     :r :t .
     { "p"     "q" :r .
         }     <.../log#implies> {:r     "p" "q" . } .

Please let me know if there are any other points to be added,

-- 
Sean B. Palmer, <http://purl.org/net/sbp/>
"phenomicity by the bucketful" - http://miscoranda.com/
Received on Thursday, 26 February 2004 12:22:33 GMT

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