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From "Scott Boag/CAM/Lotus" <Scott_B...@lotus.com>
Subject Re: XML/Database Applications . . .
Date Thu, 13 Jan 2000 18:15:12 GMT

The 'cool' way to do this is via Xalan's XLocators.  An XLocator is a kind
of driver that processes XPath LocationPaths, and is dynamically pluggable
to the XPath engine.  An XLocator returns nodes for a select statement.  By
implementing an XLocator for a given data source, you can bypass the parser
altogether, and also aid in incremental processing.  Also, it is possible
for an XLocator to take advantage of a given data source's native query
mechanism.

For a while in the LotusXSL distribution we were demonstrating an XLocator
that processed an SQL statement via the extension mechanism, and then
returned the node representations of the table data.  This is extra cool
because it means you can make parameterized stylesheets that take either a
SQL statement or part of an SQL statement, allowing you to create a
customized XML export from any JDBC database.  Nodes from various XLocators
can also be combined in the stylesheet, allowing you to mix data from
various data sources.  By subclassing the SimpleNodeLocator, this is fairly
easy to do.  Developing a full XLocator, without subclassing
SimpleNodeLocator, is harder because it involves some low-level work with
XPath navigation, and you would have to implement the search processing
yourself.

We currently aren't publishing the SQL demo because we haven't had time to
develop it to robustness, and support it.  I would love to find developers
to work on this, and also XLocators for LDAP, and other data sources.  We
would also eventually like to develop XLocators for preprocessed XML that
uses a structured index, for use with large documents.  We've also done
stuff with presenting document sets (like a directory of XML docs) as a
single source tree, which lets you effectively do XPath queries across sets
of documents.  I think XLocators are one of the best architectural features
of Xalan, and would like to see this feature developed further, and taken
advantage of by consumers.

-scott




                                                                                         
                          
                    Assaf Arkin                                                          
                          
                    <arkin@exoffic        To:     general@xml.apache.org              
                             
                    e.com>                cc:     (bcc: Scott Boag/CAM/Lotus)         
                             
                    Sent by:              Subject:     Re: XML/Database Applications . . .
                         
                    arkin@arkin.ex                                                       
                          
                    office.com                                                           
                          
                                                                                         
                          
                                                                                         
                          
                    01/11/00 11:05                                                       
                          
                    PM                                                                   
                          
                    Please respond                                                       
                          
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Check out Castor at http://castor.exolab.org.

It provides mapping between Java objects and SQL, and Java objects and
XML, works both way and supports RDBMS relations. Java to LDAP is also
coming in the next release.

We've been using it to grab an object from the database (a three-table
relation into a three-object graph) produce XML and pipe the result into
Xalan to produce an HTML page. Works like a charm, eliminates lots of
code redundancy.

arkin


"Chen, PeterX" wrote:
>
> I would like to know if the XML community at large is interested in using
an
> application that works with XML and relational databases.  Specifically,
> such an application would load an XML file into an existing table and be
> able to map the data back out from the table into an appropriate XML
file.
>
> If there is an interest in the XML community for such an application, are
> you expecting such an application to be developed by database vendors as
a
> feature in their database, or are you expecting such an application to be
> developed by third party vendors as a standalone application that works
with
> existing relational databases?  I would appreciate any and all responses.
> Thanks you.
>
> Peter





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