Re: [xml-dev] Serialization of XDM

[Mukul Gandhi <gandhi.mukul@gmail.com>]

Hello David,
   I think, I agree with you, that it's a good idea to be able to
serialize an XDM instance into some form. I would prefer an XML format
for the serialized XDM instance. i.e, perhaps we could define a XML
Schema for XDM serialization format.

But I am keen to know, what could be useful use cases, for XDM
serialization? I can think of interoperability of XDM instances
between vendros, as on the use cases for XDM serialization. But would
this really give some/any value to users (say query[XQuery] and
stylesheet[XSLT] writers)?

It seems to me, XDM serialization is like aiming to go to mars at this
point of time :)

On Sun, Sep 13, 2009 at 11:36 PM, David A. Lee <dlee@calldei.com> wrote:
> I'm dual-posting this because I think it is relevant to XML in general, but
> perhaps more so to xquery
>
>
>
> Summary (postulate)
> There is no standard or even 'community accepted' way of serializing XDM
>
> Why is this a problem
> XML languages which produce XDM (such as XPath and XQuery) and can accept
> XDM (such as XQuery and XPath through external variables) or produce XML are
> not 'closed' wrt serialization.  For example XQuery can produce things which
> have no standardized representation.  The only way to consume and produce
> these "things" are with proprietary formats, and even those only exist in
> 'in memory' language representations in general. The classic example is an
> XDM Sequence.   There is no standard or even common serialization format for
> Sequences.
> Thus an XQuery which produces a sequence (say a sequence of xs:integer)
> cannot have its output fed back into another XQuery in any standard way.
> It is true that some implementations of XQuery provide in-memory  formats
> for XDM such that the result of that vendor's XQuery can be used as input to
> that vendor's XQuery in the space of that vendor's implementation language.
>   And Some frameworks (such as .NET) provide in-memory interfaces for XDM.
>  But in general once you cross vendors or cross languages or exit the realm
> of languages there is no standardized or common way to accomplish interop
> between XDM producers and consumers.
>
> Why is this a BIG problem
> I believe one of the reasons XML has achieved its great success to date is
> due to its standardized Text serialization format.  If XML resided purely in
> the abstract space of "INFOSET" I don't believe it would have proliferated
> to even 1,000,000th as much as it has today.
> The fact that newer XML processing languages can produce datum which has no
> text serialization format is a BIG problem, IMHO.
> It means that there is no way to exchange data produced by one vendor's
> implementation  to another unless it conforms to the subset of XDM which is
> the XML Document.
> Even within *the same vendor* it is almost impossible.   For a tougher
> example, take an XQuery which produces an attribute.  There is no XQuery
> vendor that I know of that can serialize an attribute to a 'file' (or
> network, or string buffer)  and read it back even in its own implementation.
> Take even something as simple as text.   Serialize a single atomic text
> value such as "1"  and try to read it back.  Even if a vendor supports
> reading XDM from a file, (which I know of none), what type would it assign
> to "1" ?  xs:string ? xs:integer ?
>
>
> I believe this lack of standardization for serialization of XDM is both a
> "Problem" and a "BIG Problem"
> Before I extend the topic to "suggested solutions" I would love some
> feedback.
>
> Q: Does anyone else agree this is a "Problem" or a "Big Problem" ? Am I
> alone ? Why is this NOT a "Big Problem"?
> Q: Is there any known work in progress aimed at solving this problem ?
> Q: Would it be of value to solve this problem ? (and why not ?)
> Q: Would there be any interest in tackling this problem in a formal way,
> such as a W3C recommendation ?
> Q: If there were a recommendation approved would vendors be interested or
> willing to adopt / implement it ?
>
>
>
> David A. Lee
> dlee@calldei.com  http://www.calldei.com
> http://www.xmlsh.org
> 812-482-5224



-- 
Regards,
Mukul Gandhi