Zope is an Open Source object oriented web application server
written in the programming language Python. Zope stands for "Z Object Publishing
Environment". It can be almost fully managed with a web-based user interface. Zope publishes on the web Python objects that are
typically persisted in an object database, ZODB. Basic object types, such as documents, images, page templates, are available for
the user to create and manage through the web. Specialized object types, such as wikis,
blogs, photo galleries are available as third party add-ons (called products), and there is
a thriving community of small businesses creating custom web applications as Zope products.
There are two major generations of the software in use today. As of March 2005, Zope 2.7.5 is the latest stable release of
Zope 2 codebase, and Zope X3 1.0.0 is the latest release of Zope 3.
History
Zope, as it is today, appeared when its creator company, Digital Creations (now Zope Corporation), opensourced their flagship
products, Bobo and then Principia, in 1998, influenced by their venture capitalist, Hadar Pedhazur. The combination of
Bobo and Principia got renamed to Zope with this release. This move transformed Digital Creations into a services company, and
got Zope much more publicity and momentum than Principia enjoyed ever before.
Technical features
A Zope website is composed of objects in an object database as opposed to files,
as is usual with many other web server systems. This approach allows to harness
the advantages of object technologies, such as encapsulation. Zope maps URLs to objects using
the containment hierarchy of such objects; methods are considered to be contained in their objects as well.
Zope comes with the Zope Object Database (ZODB), which transparently persists (Python) objects in a transactional database.
One particularly innovative feature of Zope is its widespread use of acquisition. Acquisition is a technique parallel to class
inheritance, in which objects 'inherit' behavior from their context in a composition hierarchy, as opposed to their class in a
class hierarchy. This allows certain ways to structure source code that are otherwise harder to accomplish, and can encourage
application decomposition. A common use is in structuring the way layout elements are used in a web page. Acquisition as
implemented in Zope 2 is also perceived as a source of bugs, as it enables many unexpected behaviours. The use of acquisition has
been severely narrowed in Zope 3.
Zope provides several mechanisms for HTML templating: Dynamic Template Markup Language
(DTML), and Zope Page Templates (ZPT). DTML is a tag-based language which allows to implement simple scripting in the templates.
DTML has provisions for variable inclusion, conditions, and loops. However, DTML has major drawbacks: DTML tags interspersed with
HTML form non-valid HTML documents, and careless inclusion of logic into templates results in very unreadable code. ZPT is a
technology that fixes these shortcomings. ZPT templates can be either well-formed XML
documents or HTML documents, in which all special markup is presented as attributes in the
TAL (Template Attribute Language) namespace. ZPT offers just a very limited set of tools for conditional inclusion and repetition
of XML elements, thus the templates are usually quite simple, with most logic implemented in Python code. One significant
advantage of ZPT templates is that they can be edited in most graphical HTML editors. ZPT also offers direct support for internationalization.
Zope 2 is the base behind the Plone, Silva and Nuxeo CPS content management
systems.
Zope 3
A new version of Zope, Zope 3, has been in development for some years. Zope 2 has
proven itself as a useful framework for web applications development, but its use revealed some shortcomings. To name a few,
creating Zope 2 products involves copying a lot of boilerplate code, "magic" code that just has to be there, and the domain logic
is highly coupled with the presentation logic, so creating and maintaining tailored versions is difficult. Zope 3 is a rewrite of
the software that attempts to address these shortcomings while retaining the advantages of Zope that got it its popularity. Zope
3 is based on a component architecture. A first production release of the new software, Zope X3, was released on
November 6, 2004.
External links
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