JavaTM Product Versioning Specification
Evolution in open distributed systems needs to be managed carefully because correct operation depends
on a number of dependencies between packages. Changes within a distributed system can
have a significant impact on many groups of individuals, including users, support organizations,
web administrators, and developers. Packages within a distributed system need to operate correctly
with only partial knowledge about the state of the whole system. The difficulty level increases because
the packages of the system must be able to evolve at different rates. Evolution in such a system
is made possible by explicitly managing the dependencies between the packages using
techniques of object oriented design to govern how individual packages evolve. The Java language
defines packages that are a natural for the consistent unit of update, packages that expose only public
interfaces and that consume only public interfaces of other classes.
Introduction
In any system, support must be provided for the system to evolve over time. Most existing systems
have conventions and mechanisms that specify how change is accommodated. These systems have
been based on the model where software programs are installed on a computer. Typically, developers
specify what versions of other packages are required and the installation process verifies and
configures the system.
In open distributed systems, however, the static assumptions of existing systems do not work. Evolution
is more difficult because it is not possible to control how or when packages change. Correct
operation depends on a greater number of dependencies between packages. There is a real need for
an updated set of conventions and mechanisms which specify how packages of a system should
evolve so that the goal of an open reliable scalable distributed system can be achieved.
This document specifies the following:
· How classes, resources, and files that make up a Java package are versioned. Packages define a consistent
unit that can be developed, packaged, verified, updated, and distributed. Per package manifest information
identifies the contents of the package.
· Products are distributed by putting packages into archive files. Archives include a manifest, to identify the
product version and packages it contains.
· The standards and conventions used by developers and administrators to build and deploy products that
operate reliably as their packages and the packages they depend on are upgraded.