Apoorv's post reminded me of the extensibility requirements of a WCMS. While his approach seems to be a more pragmatic find-requirements-and-select-best-solution, I prefer the generic but extensible solutions (probably because I'm a developer/programmer at heart). Apoorv also differentiates between customization and extension, but I find it hard to draw a clear line between these two. Here's some lines on extensibility from my thesis:
The final and most important requirement of the WCMS stems from a single principle. It is impossible to predefine all requirements for a WCMS. Each year new concepts, ideas and methods are introduced to the World Wide Web, and web-sites must change the way they deliver content, content managers must change the way they produce content, and developers must change the WCMS to allow the requisite changes.
We propose that extensibility is the most important requirement of WCMS, because they have no definite set of requirements. A WCMS is an abstract information system, and users will not properly realize potential functionality before the WCMS has been put to use. The requirements are indefinite, and more functionality will be demanded as time goes by, and this is why extensibility is such a crucial requirement.
Whenever there is a new requirement and the customer is willing to pay, the functionality is sown into the existing code-base of the project.
I suggest that the improvements of functionality reduces the extensibility of the product. More code makes it harder to read and use existing code, and every decision made in the certain case of one customer makes the module unusable in the eyes of another customer. For example, the customer had a very specific requirement that each web-shop product be editable by its distributor or producer. To make this work in our CMS, the products were simply divided by distributor, and correct access privileges were granted to one distributor user for her products, respectively. For another customer, the distributor-product scheme could be completely useless, and the entire web-shop would have to be re-factored for such a purpose.
The question becomes whether the case be any different with an open source system. One point was that the we avoided changing the CMS source directly, as any changes made here would be overwritten (or have to be dealt with) on rolling out the next version of the CMS. As a result the extension was entirely made outside the core source in its own module.
The restriction of extensibility can be avoided by having a central architecture which is unnecessary to change. Such an architecture would have to be generic to adopt to possible use-cases (like the web-shop for instance), and we hope that has been achieved in the JCR. The content nodes are flexible enough to be changed into web-shop products, and the developers are confident that they would withstand other WCMS extending transformations as well.
Here's some example extensions from our customers (removed this from the thesis):
An organization selling membership-articles used their website for displaying product information on their merchandise. At one point, they decide it would be better if merchandise can be bought directly off the site and require a webshop functionality built into their WCMS.
The Norwegian Association of Allergic People daily update their website with the most recent pollen-forecast. They realize their members would like historic information and require the page to connect to a repository of pollen-numbers, where queries can produce graphs of pollen levels.
Integrating external services
A trading company see the need to feed various stock quotes on to their front page automatically. A service reading information from another site needs to be set up and connected to the WCMS.
A news-company comes up with a new category of news which should be displayed for paying-customers only. Customers gain access to this privileged part of the WCMS by entering a personal user name and password on the site.
Integrating local services
A news company decides that its web page should also display information from a data sheet (which is being constantly updated) directly onto their site. The WCMS needs a data sheet reading service which flushes its content onto a web page at regular intervals.
These are just some example applications that can be implemented outside the WCMS, but sooner or later they need to interconnect in some way or the other, and the system will have to be modified to allow this connection.