[DFDL-WG] DFDL character entities in DFDL expressions
Tim Kimber
KIMBERT at uk.ibm.com
Wed Dec 5 08:28:19 EST 2012
The key point for me is this: what happens when a DFDL expression ( which
looks exactly like an XPath 2.0 expression ) gets lifted out of the DFDL
xsd and used by a non-DFDL XPath processor? If we allow the DFDL entities
to be used like XML entities then the expression will appear to be a valid
XPath expression, but it will fail in some unpredictable way. On the
other hand, if DFDL entities can only be used in conjunction with a DFDL
function then (presumably ) the non-DFDL XPath engine will report that an
unknown extension function is being used.
regards,
Tim Kimber, DFDL Team,
Hursley, UK
Internet: kimbert at uk.ibm.com
Tel. 01962-816742
Internal tel. 37246742
From: Mike Beckerle <mbeckerle.dfdl at gmail.com>
To: Andrew Coleman/UK/IBM at IBMGB,
Cc: Steve Hanson/UK/IBM at IBMGB, Tim Kimber/UK/IBM at IBMGB,
dfdl-wg at ogf.org
Date: 05/12/2012 13:17
Subject: Re: [DFDL-WG] DFDL character entities in DFDL expressions
Well, yes, I think we're discussing exactly how that should work.
No matter what, we do need to be clear that string values created in
DFDL's expression language can contain these XML-illegal characters, since
they are allowed in DFDL's infoset. This means that DFDL implementations
can only re-use an existing XPath implementation to create their DFDL
expression language implementation to the extent that it does NOT enforce
the XML-illegal characters restrictions all over the place.
I am currently working with standard Saxon-B XPath and will report back.
But let's be optimistic. The question then is just what is the solution to
creating a string-literal including these characters. That cannot be done
without some beyond-XML mechanism. DFDL has a string-literal notation for
expressing these characters, so we either say that string literals in the
expression language can use the DFDL character and numeric entities, or we
can do something more 'library like', and provide a function which
interprets the string-literal notation, and isolate the implementation
concerns a bit.
As a language embedded in XML schema, we already straddle the fence of two
somewhat inconsistent language environments.
E.g., the literals one can use as the value of the default attribute on an
element declaration cannot use DFDL character entities, as this is a
purely XML Schema construct.
Similarly, the regular expressions one can use for the XML schema pattern
facet are more restrictive than the DFDL regular expressions one can use
in a dfdl:assert, or a dfdl:lengthKind='pattern'.
So, it's acceptable to me to say that expressions also have some split
where the dfdl-specific aspects, like the dfdl character and numeric
entities notation, is isolated in a sub-construct.
On Wed, Dec 5, 2012 at 6:37 AM, Andrew Coleman <andrew_coleman at uk.ibm.com>
wrote:
No, casting a hexBinary to a string will just write out the octets - i.e.
the string will be '00'.
XPath itself has no mechanism for interpreting entity references or
character references. Its hosting language (XQuery or XSLT/XML) provides
this. Since DFDL is XML, wouldn't that provide a mechanism?
Regards,
- Andy
__________________________________________
Andrew Coleman
WebSphere Message Broker Development
IBM Hursley Park
From: Steve Hanson/UK/IBM
To: Tim Kimber/UK/IBM at IBMGB,
Cc: dfdl-wg at ogf.org, dfdl-wg-bounces at ogf.org, Mike Beckerle <
mbeckerle.dfdl at gmail.com>, Andrew Coleman/UK/IBM at IBMGB
Date: 05/12/2012 11:06
Subject: Re: [DFDL-WG] DFDL character entities in DFDL expressions
Aren't XPath facilities sufficient here?
outputValueCalc="{ if (fn:string-length(../s) lt 64) then
fn:concat(../s, xs:string(xs:hexBinary('00'))) else ../s }"
Regards
Steve Hanson
Architect, Data Format Description Language (DFDL)
Co-Chair, OGF DFDL Working Group
IBM SWG, Hursley, UK
smh at uk.ibm.com
tel:+44-1962-815848
From: Tim Kimber/UK/IBM at IBMGB
To: Mike Beckerle <mbeckerle.dfdl at gmail.com>,
Cc: dfdl-wg at ogf.org, dfdl-wg-bounces at ogf.org
Date: 05/12/2012 10:51
Subject: Re: [DFDL-WG] DFDL character entities in DFDL expressions
Sent by: dfdl-wg-bounces at ogf.org
I think the restriction was aimed at avoiding things like this:
outputValueCalc="{ if (fn:string-length(../s) lt 64) then
fn:concat(../s, '%#rFF;') else ../s }"
I agree that a total ban is too restrictive. My personal preference would
be for the dfdl:string() function because it makes the usage of
DFDL-specific features obvious in the DFDL expression. But what would be
the return type of dfdl:string()? It it returned a sequence of characters
then the raw byte entity ( %#rnn; ) would still need to be disallowed.
regards,
Tim Kimber, DFDL Team,
Hursley, UK
Internet: kimbert at uk.ibm.com
Tel. 01962-816742
Internal tel. 37246742
From: Mike Beckerle <mbeckerle.dfdl at gmail.com>
To: dfdl-wg at ogf.org,
Date: 04/12/2012 23:36
Subject: [DFDL-WG] DFDL character entities in DFDL expressions
Sent by: dfdl-wg-bounces at ogf.org
We currently have this language in the spec:
"Within an expression, a string is never interpreted as a DFDL string
literal."
To me this means one cannot use DFDL character entities in an expression.
However, I need to do this:
outputValueCalc="{ if (fn:string-length(../s) lt 64) then
fn:concat(../s, '%NUL;') else ../s }"
Basically, I need to append a NUL on the end of the string in the output
value case.
Unless I can put a %NUL; into an expression and have it interpreted as a
DFDL String literal, I am not sure how I can achieve this.
At minimum I need a new DFDL function which might be an alternate string
constructor, such as dfdl:string('....') which interprets the argument as
something where the contents are to be scanned for DFDL character entities
and they are substituted so that the resulting string can contain the
characters that are disallowed in XML. (like NUL)
--
Mike Beckerle | OGF DFDL WG Co-Chair | Tresys Technologies
Tel: 781-330-0412
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Unless stated otherwise above:
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741598.
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--
Mike Beckerle | OGF DFDL WG Co-Chair | Tresys Technologies
Tel: 781-330-0412
Unless stated otherwise above:
IBM United Kingdom Limited - Registered in England and Wales with number
741598.
Registered office: PO Box 41, North Harbour, Portsmouth, Hampshire PO6 3AU
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