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   RE: SAX Future

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  • From: Ronald Bourret <rbourret@ito.tu-darmstadt.de>
  • To: "XML Developers' List" <xml-dev@ic.ac.uk>
  • Date: Mon, 16 Nov 1998 12:38:10 +0100

Michael Kay wrote:

> Are there any other areas where you can get multiple implementations of the
> same Java interface from different suppliers? If so, how do they solve the
> version control problem? Or have we achieved a first?

One that comes quickly to mind is JDBC, where each driver implements the same interfaces.  In JDBC 2.0, Sun has added methods to existing interfaces but has not (as far as I can tell) changed any 1.0 methods.  They have also added completely new interfaces and packages.

The version control problem is solved by two mechanisms:
* 100% backwards compatibility
* The ability of the application to query the version of the spec to which a given driver conforms.

The first point solves the problem of 1.0 applications working with 2.0 drivers.  Because 2.0 is a superset of 1.0, a 2.0 driver necessarily implements everything a 1.0 application uses.

The second point solves the problem of 2.0 applications working with 1.0 drivers.  The application queries the version of the spec supported by a driver and then only uses the functionality in the supported version.  If the application requires 2.0 functionality, it simply refuses to work with a 1.0 driver.

-- Ron Bourret

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