cziegeler 2004/04/23 01:42:41
Modified: src/documentation/content/xdocs site.xml
Added: src/documentation/content/xdocs versioning.xml
Log:
Add first draft of versioning guide
Revision Changes Path
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Index: site.xml
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RCS file: /home/cvs/cocoon-site/src/documentation/content/xdocs/site.xml,v
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<!--|
| Guidelines shouldn't be put live before they are properly voted
upon.
| <guidelines label="Guidelines" href="guidelines.html"/>
+ | The same applies to our versioning guide
+ | <versioning label="Versioning" href="versioning.html"/>
|-->
<history label="History" href="history.html"/>
1.1
cocoon-site/src/documentation/content/xdocs/versioning.xml
Index: versioning.xml
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<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE document PUBLIC "-//APACHE//DTD Documentation V1.2//EN"
"document-v12.dtd">
<document>
<header>
<title>The Apache Cocoon Versioning Manifesto - DRAFT</title>
</header>
<body>
<warning>DRAFT INITIAL VERSION</warning>
<p>
This document covers how the Cocoon project is versioned.
Since Cocoon is a framework, it is very important to define a stable
API
for users and developers. However, we also need to move Cocoon forward,
technologically. To balance these two needs, a strict policy of
versioning
is required, which users can rely upon to understand the limitations,
restrictions, and the changes that can occur from one release to the
next.
</p>
<section id="basics">
<title>Basics</title>
<p>
Versions are denoted using a standard triplet of integers:
</p>
<p>
MAJOR.MINOR.PATCH.
</p>
<p>
The basic intent is that MAJOR versions are incompatible, large-scale
upgrades of the API. MINOR versions retain usage and extension
compatibility
with older minor versions, and changes in the PATCH level are
perfectly
compatible, forwards and backwards.
</p>
<p>
Following the main design principle of Cocoon, the pyramid of
contracts,
we distinguish between users and developers of Cocoon.A very rough
distinction
between them is that a user writes the application using Cocoon
without
coding Java. There is one exception to this rule: flow script - the
java
script is also written by the user.
</p>
<p>
A developer codes Java and provides additional functionality for the
user,
so a developer extends Cocoon.
</p>
<p>
Therefore we distinguish between usage compatibility (user API) and
extension compatibility (developer API). Both compatibility levels
cover
some kind of "source" compatibility. Cocoon does not provide binary
compatibility. But as Cocoon is distributed as a source release that
you have to compile anyway, it's saver to compile your own
application
code (if any) using the version of Cocoon that your application runs
on.
</p>
<p>
There are several reasons why recompilation is recommended. We
strongly
advise to compile Cocoon (or any other Java application) with the same
JDK that is later used in production.
</p>
<ul>
<li>
Ensures that you have reliable operating environment. For example if
you compile a Java application with JDK 1.4 in JDK 1.3 compatible
mode
it still can happen that your application doesn't run properly with
JDK 1.3!
This is not Cocoon specific!
</li>
<li>
Allows you to easily configure which parts you want. The selection
of
wanted blocks is currently evaluated at build time, so if you want
to have an additional block/remove a block in your Cocoon
installation,
you have to rebuild Cocoon.
</li>
<li>
You'll get warned of deprecated parts of the API.
</li>
</p>
</section>
<section id="usage-compatibility">
<title>Usage Compatibility</title>
<p>
<em>Usage</em> compatibility guarantees that an application written
by
a Cocoon user is compatible. All files developed by a typical Cocoon
user like xml files, sitemaps, stylesheets (elements and namespace
declarations)
keep on being picked up by the machinery and are dealt with correctly
(sitemap semantics, generator/transformer-picked up elements, config
file entries...).
</p>
<p>
In fact this should cover everything (including flow script) but
except
own Java code.
</p>
<p>
Applications that write against a particular version will remain
usage
compatible against later versions, until the major number changes.
</p>
<p>
Writing an application against a version means that this application
does not use any deprecated API of that version. Therefore minor
version
changes are only usage compatible from one minor version to the
direct
following one. For example 2.2 is usage compatible to 2.1. But 2.3 is
not
necessarily usage compatible to 2.1, although it is usage compatible
to 2.2. As long as you don't use deprecated API (and the API you rely
on does not get deprecated), your application is usage compatible
across
all minor versions.
</p>
<p>
Example:
</p>
<ul>
<li>a feature is introduced in 2.0 and used by the application.</li>
<li>it is deprecated in 2.2</li>
<li>it will be removed in 2.3</li>
</ul>
<p>
If the time inbetween two minor releases is very short, then it might
happen that deprecated parts will be kept in the following minor
release
and are removed in a follow-up minor release. This is in order to
ensure
that users have time to update their applications if they use the
deprecated
parts.
</p>
<p>
However, if an application uses an API which has become available in
a
particular minor version, it (obviously) will no longer operate
against
previous minor versions.
</p>
</section>
<section id="extension-compatibility">
<title>Extension Compatibility</title>
<p>
<em>extension</em> compatibility guarantees that own extensions to
what
Cocoon provides (own Java classes that interface directly with API in
the
Cocoon distribution) compile and operate.
</p>
<p>
Applications that write against a particular version will remain
extension
compatible against later versions until the major or the minor number
changes (Please note the difference to the usage compatibility).
However,
the Cocoon developers take care that even if the minor number
changes,
most of the own code still works and operates properly. Incompatible
changes between minor versions are kept to a minimum. Frequent new
releases
of Cocoon ensure that developers have a smooth transition path.
</p>
<p>
If an interface/class changes in an incompatible way between minor
version changes, the Cocoon documentation will contain a detailed
update
guide that contains a solution for every incompatible change. So
following
this guide should make the update smoothly.
</p>
</section>
<section id="exceptions">
<title>Deprecation and Exceptions</title>
<p>
To continue the Cocoon development and to keep up with the
innovations,
parts of Cocoon might get deprecated; this includes parts of the user
API and also parts of the developer API.
</p>
<p>
If a part of the user API is deprecated, this will be flagged through
run-time warnings that appear in the logs but remain supported. This
indicates that an upcoming minor (or major) release will no longer
support this.
</p>
<p>
If a part of the developer API is deprecated it will be removed with
the next major, minor or patch release. However, the need for removing
deprecated stuff between two patch releases is really very rare and
will only happen if the cost of keeping it is much higher than the
cost that might occur for updating the application.
</p>
<p>
For developers there is one exception to this rule: private API.
Cocoon
has some internal classes and interfaces that are not meant to be used
by a Cocoon developer (someone extending Cocoon). These pieces of
Java code are clearly marked in the Javadocs and should not be used.
They might change even between a patch version change in an
incompatible
way without providing a workaround!
</p>
</section>
<section id="blocks">
<title>Blocks and Block Stability</title>
<p>
Cocoon currently allows optional functionality to be included or
excluded
using a simple system called blocks, in which the functionality is
included
or excluded at compile time.
</p>
<p>
[NB. This is a precursor to a more complete block system which is
currently under development.]
</p>
<p>
A block can have one of three statuses: unstable, stable or
deprecated.
An unstable block has an API that can change without notice. A stable
block
is subject to the same versioning process as described in this
document.
Similarly, when the entire functionality of a block is deprecated, it
will
be handled in the same way as any other deprecated code within Cocoon.
</p>
</section>
<section id="external-libs">
<title>External Libraries</title>
<p>
Cocoon uses a set of external libraries (like for example Avalon,
Xalan or Xerces). Inbetween any release, even patch releases,
the versions of the external libraries might be updated to any
version.
Cocoon only updates external libraries if there are good reasons
for it, like important bug fixes or new features that will be
used by the new Cocoon version.
</p>
<p>
Therefore if your application is written against a special API of an
external library it might be that this API of the external library
changes inbetween two Cocoon versions and therefore your application
does not work properly anymore (or even does not compile anymore).
Unfortunately, this issue is out of the scope of Cocoon.
</p>
<p>
The documentation of Cocoon contains a list of the libraries and the
version changes between libraries from one Cocoon release to another.
</p>
</section>
<section id="examples">
<title>Exsamples</title>
<p>
Here are some examples to demonstrate the compatibility:
</p>
<!-- TODO: Change the format: -->
<p>
Original Version New Version Usage Compatible Extension
Compatible
</p>
<p>
2.2.3 2.2.4 Yes Yes
</p>
<p>
2.2.3 2.3.1 Yes No
</p>
<p>
2.2.3 3.0.0 No No
</p>
<p>
Note: while some of the cells say "no", it is possible that the
versions
may be compatible, depending very precisely upon the particular APIs
used by the application.
</p>
</section>
<section id="repositories">
<title>Versioning and Repositories</title>
<p>
Cocoon is very innovative and new features are added very frequently.
This
results in new functionality that justify a minor version change on
its own.
In addition, to move Cocoon forward technologically, some features
have
to be removed/deprecated which of course results in a minor version
change
as well.
</p>
<p>
So, Cocoon will potentially release several versions with minor
version
changes in a year and only a few patch releases. Of course, if a patch
release is required, for example if a potential security issue is
found
etc., the patch release will be made available asap.
</p>
<p>
This high innovention has - at least in theory - the price of
maintaining
several branches at once in order to be able to apply patches to older
versions.
</p>
<p>
To reduce this to a minimum, Cocoon uses one repository per major
version.
The HEAD of the repository always contains the latest version. If a
new
minor release is required, the version in the repository is directly
changed
to this minor version (e.g. from 2.1.4 to 2.2). The current state is
tagged and if the need for a 2.1.5 release arises, a branch is
created.
</p>
<p>
However, due to the compatibility rules explained above, there should
only
be a reason for a patch version if major problems occur (like security
issues). In any other case, the Cocoon community expects the
applications
to migrate to the new minor version release which should be fairly
simple.
</p>
<p>
In addition Cocoon has a sandbox repository to test new features.
</p>
</section>
<section id="reality">
<title>Realitiy</title>
<p>
The above expresses the intentions of the cocoon community to support
a
release management contract to all the users of the framework.
However
reality observes that the path to hell is paved with goood
intentions.
In case anyone finds clear violation or signs of potential problems
of these
good intentions he/she should report those to [email protected]
in order
to let proper action be taken (which might be reverting some changes
and/or
assigning a different version number).
</p>
<p>
If you have read this, you might get the impression that updating your
application from one Cocoon to another one will be very time
consuming.
Or that we are acting arbitrarily in deprecating stuff here and there.
</p>
<p>
Of course this is not the case :) Before we introduce new features,
new
API we discuss this in great detail, so this should reduce potential
errors in the design to a minimum. In addition, deprecating stuff is
also handled with great care. So, in the end, this guide establish
rules that detail how we handle such rare situations. It is not a
free ticket for the Cocoon developers to deprecate/change/remove stuff
like they want.
</p>
</section>
</body>
</document>
