• From: "Radu Cernuta" <radu.cernuta@g...>
• To: noah_mendelsohn@u...
• Date: Thu, 10 Apr 2008 20:02:51 +0200

I agree with all that has been said here.  There is just one thing I'd
like to add regarding RELAX NG's approach to data types: you can do
just about anything, provided you write a data type library, in case
nobody wrote it for you.

An article about it here:
http://www-128.ibm.com/developerworks/xml/library/x-custyp/

Radu Cernuta

2008/4/10, noah_mendelsohn@u... <noah_mendelsohn@u...>:
> I agree with everything Mike says.  Furthermore, while it's true that
> RelaxNG is the simpler, cleaner, and in certain dimensions more powerful
> language, and with a nicer syntax, one can make the case that XSD has
> technical advantages for certain scenarios as well.  There is a tradeoff
> between building languages in which the parse is deterministic (XSD) vs.
> non-deterministic (RelaxNG).  RelaxNG, for example, has a very nice story
> about closure under intersection/union/difference:  you can always write a
> RelaxNG schema that accepts just exactly what is accepted by any two other
> RNG schemas, what's accepted by either of them, etc.  XSD can't in general
> do the equivalent.  On the other hand, I would claim that XSD has a
> stronger story regarding type assignment, and it has a stronger story
> about static typing.  The XQuery language uses XSD as its type system. You
> can, for example, declare in XSD a type called "Measurement" that has
> calls for a decimal number as the element content, with an attribute
> specifying units such as "inches" or "cm".  You can use that type in your
> schema to declare elements named "Width" and "Height", which you can show
> in advance will always accept the same content.  Furthermore, you can
> define XQuery functions which return as their value a such a Measurement.
> It would be interesting to see how the XQuery language would change if
> RelaxNG were used as the base typing system.  I'm not saying the results
> would be bad, but I'm fairly sure they would be different.  For similar
> reasons, I think you can make the case that XSD has a stronger story about
> databinding, particular binding into systems that themselves are
> statically typed.  The obvious binding of the above example to Java or
> .Net is a class called "Measurements", and member variables called "width"
> and "height".  Because the to variables are of the same type, they are
> assignment compatible:  you can write width=height; and it will work.  You
> can do Java and .Net databinding with RelaxNG, but I think it works best
> with a deterministic subset of the language, and I think it's fair to say
> that RelaxNG doesn't give as much attention to facilitating the assignment
> of compatible types in examples like this.
>
> So, in addition to all the factors that Mike lists, I think there are
> non-trivial technical tradeoffs.  Some of them do strongly favor RelaxNG
> for many purposes, but XSD has some technical strengths as well, and some
> of those are exploited by systems like XQuery and by various databinding
> frameworks.   (I should say, for those who don't know me, that I was
> involved to a significant degree with the design of XSD.  I've tried to
> make the above a balanced analysis, but it's certainly possible that
> reasonable people would see things differently.)
>
> Noah
>
> --------------------------------------
> Noah Mendelsohn
> IBM Corporation
> One Rogers Street
> Cambridge, MA 02142
> 1-617-693-4036
> --------------------------------------
>
>
>
>
>
>
>
>
> "Michael Kay" <mike@s...>
> 04/09/2008 05:22 AM
>
>         To:     "'Ben Stover'" <bxstover@y...>, "'xml-dev'"
> <xml-dev@l...>
>         cc:     (bcc: Noah Mendelsohn/Cambridge/IBM)
>         Subject:        RE:  What is the "market share" of Relax
> NG vs XSD schema ?
>
>
> >
> > Why is Relax NG not becoming popular?
> > Looking at its properties and advantages over XSD it should
> > become the one and only schema defintion language
> >
>
> It's an old story. Why did the Dvorak keyboard not become popular? Why
> aren't we all using Macs? Why do we use ludicrously insecure email
> protocols
> that flood the world with spam, when we could have adopted X.400?
> Technical
> quality was never enough to ensure success; the world will not beat a path
> to your door just because you have a better mousetrap.
>
> When it comes to standards adoption, most people will not adopt X unless
> they believe that everyone else will adopt X. So success depends on having
> a
> convincing endorsement from organizations that have the reputation to
> either
> predict the future or create it. Relax NG has never had that endorsement.
> (And indeed, ISO doesn't have that reputation.)
>
> Michael Kay
> http://www.saxonica.com/
>
>
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