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Eric,
I am not familiar with E4X (I should look into it), but I have
looked at Cw. The main difference between us and Cw is that we have taken
conformance to the XML Schema, XPath, and XML standards (such as
Namespaces) as a design priority. This leads to different design choices.
So here are some differences (in no particular order)
1. There is no distinction between C# classes and XML classes in Cw (for
the most part). In one sense this is elegant, but it requires compromise
in both the C# and XML type systems. So in an early paper on Cw, Erik
Meijer writes, "After this comparison we will argue that the inherent
impedance mismatch between the XML and object data-models suggests that we
should both modify the host object language to enhance XML support and
compromise full XML fidelity" [
http://research.microsoft.com/~emeijer/Papers/XML2003/xml2003.html#S3.3].
In XJ, we made a slighly different design choice -- XML Types are
subclasses of a
special class XMLObject -- all other Java classes behave as per the Java
spec. Subclasses of XMLObject behave according to the XML Specs -- from
the Java perspective they are just classes with no fields and a few
methods inherited from XMLObject. One can execute XPath expressions on
them, construct them from literal XML, etc.
2. XJ supports the full set of XPath 1.0 expressions. Cw introduces a new
syntax for specifying a subset of XPath expressions (e.g c..f == c//w)
3. Types in XJ are XML Schema types (element declarations). Subtyping in
XJ is based on XML Schema subtyping and substitution groups. Schemas may
be "imported" [Schemas behave analogously to packages in Java, and
element declarations are similar to class declarations]. In Cw, types are
"regular expression types" and I believe they provide a tool for
converting XML Schema types into C# classes. Subtyping is structural
(independent of XML schema).
4. XJ supports use of Namespaces in XML construction and XPath evaluation.
I am not sure what Cw's position on this is (I haven't seen a use of
namespaces in their examples).
5. Cw supports mechanisms for accessing relational data --- we do not.
6. XJ supports in-place updates (not available in the current prototype).
AFAIK, Cw does not.
All in all, at a suitably abstract level both languages are similar ---
they let programmers program with XML more easily. The different design
principles --- unify objects and XML (Cw) and high-fidelity to XML
standards (XJ) leads to a different feel to each language.
BTW, in the research community there have been several language
integrations of XML into a programming language, e.g. Xact, Xtatic
(originated from XDuce), CDuce, XOBE, ....., each with a slight different
feel to it.
A technical paper on XJ is available from
http://www.research.ibm.com/xj/pubs. It'll be presented at WWW 2005 next
month.
Mukund Raghavachari
IBM T.J. Watson Research Center
http://www.research.ibm.com/people/m/mrm
XJ: the XMLification of Java (http://www.research.ibm.com/xj)
Eric van der Vlist <vdv@dyomedea.com>
04/14/2005 02:30 AM
To
xml-dev@lists.xml.org
cc
Subject
Re: [xml-dev] [ANN] XML Enhancements for Java 1.0
Hi,
On mer, 2005-04-13 at 13:29 -0400, Mukund Raghavachari wrote:
> We have released a prototype compiler and runtime system on Alphaworks (
> http://www.alphaworks.ibm.com/tech/xj). XJ is an evolving language, and
we
> are extremely interested in feedback on the utility of its features. We
> are interested in what people think about "tight" integration of XML
into
> Java. Our opinion is that it makes XML processing applications more
> efficient and robust.
That sounds very cool!
To me, that's closest to things such as E4X for EcmaScript or C-Omega
for C# than to binding frameworks.
Am I right? Can you elaborate on the differences and similarities with
these other projects (other than, of course that Xj is for Java!)?
Are you aware of other similar projects for Java or other languages?
Thanks,
Eric
>
--
Weblog:
http://eric.van-der-vlist.com/blog?t=category&a=English
------------------------------------------------------------------------
Eric van der Vlist http://xmlfr.org http://dyomedea.com
(ISO) RELAX NG ISBN:0-596-00421-4 http://oreilly.com/catalog/relax
(W3C) XML Schema ISBN:0-596-00252-1 http://oreilly.com/catalog/xmlschema
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