Implementation issue with the OXCI XML Interface Specifications

["Cabral, James E." <JCabral@mtgmc.com>]

OXCI participants and LegalXML ECF TC members:

Over the last two weeks, Counterclaim has been testing the XML schemas
and instance documents provided in the draft OXCI XML Interface
Specifications document and has encountered a significant issue that we
felt should be brought to the attention of the OXCI pilot sites and
LegalXML before our meetings to discuss the specifications next Tuesday.

As you know, OXCI is developing an open-source implementation of an
Electronic Filing Manager (EFM) that will eventually support the
LegalXML Court Filing Blue specification.  Because the Court Filing Blue
specification is still in the requirements phase, the OXCI XML Interface
Specifications are intended to provide an interim set of interface
standards based on the Global Justice XML Data Model (GJXDM) 3.0
operational release.  You can find all the OXCI design documents at 

http://oxci.sourceforge.net

For a number of reasons, most importantly the fact that the a subset
schema generator tool is not yet available, the OXCI schemas import the
full GJXDM schema. The OXCI schemas then use type restriction to add
constraints (such as required elements) and type extension to add
additional elements specific to court filing.  The OXCI schemas also
include provisions for local courts to add additional elements and
constraints through type extension/restriction and type substitution. 

Counterclaim and MTG have successfully validated the GJXDM schemas, the
OXCI schemas and the OXCI example instances using XMLSpy and the
Xerces-based validation tool provided by GTRI.  However, Counterclaim
has not been successful in generating Java objects from the XML schemas.
To date, they have tested the Java API for XML Binding (JAXB) reference
implementation, JaxMe, an open source implementation of JAXB, and
Castor.  They have also tested several Windows code generation tools,
including LiquidXML and Breeze XML Binder, but they have also failed to
generate code.  Some of these tools have even failed to validate the
schemas.

The issue appears to be the fact that none of these tools implement the
full W3C XML Schema specification.  Specifically, the code generation
tools we have tested do not support type restriction.  This appears to
be a well-known limitation - Jim Beard from Counterclaim has
corresponded with other developers who have experienced problems
implementing this feature in their applications.  In addition, he
received the following response from someone at Sun Microsystems:

 "From what you've described, it does not sound like there is anything
illegal in your schemas.  The problem is that this type of schema
derivation hierarchy is very difficult to map to a Java object
inheritance hierarchy.  Java has no concept of 'derivation by
restriction' - roughly speaking, there is no way for a sub-class to only
inherit a portion of it's base class.  The JAXB spec (sec 5.3.2) sort of
glosses over this issue because there really isn't a good solution.  It
covers simple derivation by restriction, but handling a type that
derives by extension from a type that derives by restriction is a whole
other beast.  As a result, the RI (reference implementation) punts on
the issue and flags it as an error."

If we cannot find code generation tools that support the current
approach, we are considering the following options:

1.	We could generate the Java objects manually.  However, this
increases the development and support complexity of the code
considerably and makes it difficult to adapt the code later to support
the Court Filing Blue specification.

2.	We could use subset schemas rather than importing the full
GJXDM.  This approach is recommended by GTRI.  However, there are not
yet any documented procedures or examples for manually developing subset
schemas and the subset schema generator tool is currently scheduled to
be available in April.  For more information on this approach, see
GTRI's explanation of customized schemas at 
http://justicexml.gtri.gatech.edu/technical/customized-schemas/index.htm
l

3.	We could adopt a different approach for developing schemas based
on the elements of the GJXDD.  Specifically, there may be more modular
ways to construct schemas that use the Justice XML data dictionary but
are not necessarily compliant with the Justice XML data model.

4.	Other options?

Options 2 and 3 would require significant changes to the current OXCI
XML Interface Specifications but may significantly simplify
implementation.  Regardless of the approach we choose in the short term
for this project, the OXCI implementation must eventually support the
Court Filing Blue specification.  Our hope is that the LegalXML ECF TC
can benefit from the OXCI project and adopt an approach to Court Filing
Blue that is both practical to implement and consistent, as appropriate,
with the GJXDM.

I will add this to our agendas for discussion on Tuesday.

  Thanks,

Jim Cabral
James E. Cabral Jr., Senior Associate

The information transmitted is intended only for the person or entity to
which it is addressed and may contain confidential and/or privileged
material.  If you received this in error, please contact the sender and
delete the material from any computer.