[DFDL-WG] checking on 'no recursion' restriction - are we sure we can live without it

[Mike Beckerle]

I take your point on JSON. We don't need to solve that problem really.

At this point we have to put out a call for examples of recursive
definitions in data formats, i.e., where one really needs recursion to
model the data.

I can imagine they exist, but have not had to use one, nor seen one. I have
seen things that were Lisp S-Expression-like syntax, but they were probably
flattenable, i.e., no true recursion needed.

I checked EDIFACT, and they allow nesting, but they specifically cut it off
at 1 level of nesting. DOCBOOK has an SGML variant, but that's so XML-ish,
that I really don't see that it is DFDL's job to be able to parse that.

Any other examples?





On Mon, Apr 9, 2012 at 5:03 PM, Tim Kimber <KIMBERT at uk.ibm.com> wrote:

> Recursion would help, but I suspect that you would still end up with a
> DFDL info set that was structured in a non-ideal way. The info set would be
> a tree in which all of the 'real' elements would have the same name. The
> JSON names would have to be carried on a child element 'jsonName'. Most
> clients applications would want to transform that DFDL info set into
> something more natural. One solution would be to add a new feature to DFDL
> to allow the info set element name to be calculated from the data using a
> DFDL expression - but then the DFDL info set would not be valid for the
> DFDL xsd.
>
> Looking at this another way, JSON is like XML - they are both
> self-defining formats allowing arbitrarily deep nesting. In both cases you
> can add some external rules that describe the expected structure of the
> document ( e.g. XSD for XML ) .  I think DFDL is designed for the case
> where the structure is known in advance. The 'generic JSON parser' or
> 'generic XML parser' are solved problems.
>
> regards,
>
> Tim Kimber, Common Transformation Team,
> Hursley, UK
> Internet:  kimbert at uk.ibm.com
> Tel. 01962-816742
> Internal tel. 246742
>
>
>
>
> From:        Suman Kalia <kalia at ca.ibm.com>
> To:        Mike Beckerle <mbeckerle.dfdl at gmail.com>
> Cc:        dfdl-wg at ogf.org, dfdl-wg-bounces at ogf.org
> Date:        09/04/2012 12:27
> Subject:        Re: [DFDL-WG] checking on 'no recursion' restriction -
> are we sure we can live without it
> Sent by:        dfdl-wg-bounces at ogf.org
> ------------------------------
>
>
>
>
> I tried to search XML schema definition for JSON but could not find it..
>  If you have please attach.  You can build models without using recursion.
>  Adding recursion to the spec will certainly increase complexity.
>
>
>
> From:        Mike Beckerle <mbeckerle.dfdl at gmail.com>
> To:        dfdl-wg at ogf.org
> Date:        04/06/2012 05:49 PM
> Subject:        [DFDL-WG] checking on 'no recursion' restriction - are we
> sure we can live without it
> Sent by:        dfdl-wg-bounces at ogf.org
>  ------------------------------
>
>
>
>
> DFDL v1.0 spec currently disallows recursive types.
>
> Are we sure we can live without this?
>
> Seems to me there are many formats e.g., JSON, which are popular now, and
> which naturally require recursion to express.
>
> There are a number of document-like formats - there's a fuzzy grey area
> where documents and data records overlap, and these will naturally be
> modeled using recursion.
>
> Even formats like EDIFACT allow segment nesting, though I'm not sure about
> whether recursive definitions are allowed or precluded, a generic EDIFACT
> parser wouldn't know any specific segment types, and would want to have a
> recursively defined generic segment structure.
>
> Comments?
>
> ...mikeb
>
> --
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> Tel:  781-330-0412
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-- 
Mike Beckerle | OGF DFDL WG Co-Chair
Tel:  781-330-0412
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