[DFDL-WG] Issue 168 - Re: Fw: Escape scheme properties that can be expressions

[Mike Beckerle]

In the absence of a compelling reason to allow relative paths here, I think
the conservative choice is to retain this rule from 6.3.2.

However, I did think about this and my evaluation on this topic is that
allowing relative paths makes things just a little more complicated
analytically to insure one gets good performance, but as DFDL does not
allow recursive types, it is a relatively simple analysis to convert any
relative path use in DFDL into absolute paths. So I am not worried about
there being performance impact.

...mikeb

On Mon, Apr 2, 2012 at 7:30 AM, Steve Hanson <smh at uk.ibm.com> wrote:

> We took action 168 on the last call to discuss the issue of relative paths
> in expressions for properties in global formats.
>
>   *168*
> *Relative path expressions in global annotations (Mike)*
> 28/03: Mike to check that allowing relative paths does not cause
> performance problems for an implementation.
> 05/04:
>
>
> Just seen this in section 6.3.2. of the spec:  "DFDL expressions that are
> used to provide the value of DFDL properties in the dfd:format annotation
> on the xs:schema MAY NOT contain relative paths".
>
> Regards
>
> Steve Hanson
> Architect, Data Format Description Language (DFDL)
> Co-Chair, *OGF DFDL Working Group* <http://www.ogf.org/dfdl/>
> IBM SWG, Hursley, UK*
> **smh at uk.ibm.com* <smh at uk.ibm.com>
> tel:+44-1962-815848
> ----- Forwarded by Steve Hanson/UK/IBM on 02/04/2012 12:28 -----
>
> From:        Steve Hanson/UK/IBM
> To:        dfdl-wg at ogf.org
> Date:        14/03/2012 16:09
> Subject:        Escape scheme properties that can be expressions
> ------------------------------
>
>
> The spec allows the escapeCharacter and escapeEscapeCharacter of DFDL
> escapeScheme to be expressions, in case the characters are supplied
> dynamically in the data stream.
> However given that escape schemes are defined globally, should these
> properties be permitted to take relative paths in the expression?
> Today the spec implicitly allows this, meaning an implementation can not
> entirely validate an escapeScheme annotation up front, but must validate
> escapeCharacter and escapeEscapeCharacter at each point of use.
> I'm not sure it makes much sense for the path to be anything than absolute.
>
> Regards
>
> Steve Hanson
> Architect, Data Format Description Language (DFDL)
> Co-Chair, *OGF DFDL Working Group* <http://www.ogf.org/dfdl/>
> IBM SWG, Hursley, UK*
> **smh at uk.ibm.com* <smh at uk.ibm.com>
> tel:+44-1962-815848
>
>
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> 741598.
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-- 
Mike Beckerle | OGF DFDL WG Co-Chair
Tel:  781-330-0412
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