How to organise intermodule integration in a modular project?

Question

I'm currently writing my own PHP Framework (yes, another one) for studying purposes. I'll actually try to use it as my graduation dissertation.

After two failed attempts, I've finally found a way to develop it in a modular architecture, like Zend and Symfony.

I have some loosely coupled modules that can work apart from each other, but their usability would be better if I stick them together.

Now I'm wondering the best way of integrate them. I'm not willing to put a module as requirement for the other, because this breaks the modular design.

My first idea was to create a different module that requires the other two and put them to work together. This would work fine when I have just two modules, but when I have a module that can be integrated with two or more modules I get lost.

Should I create one module for each possible integration? Or should I create just one module and put all integrations I could have there?

Am I clear? If not, I'll try to explain it better.

Edit:

A practical example.

My Data Access Layer implements the Table Row Gateway pattern. I have a TableGatewayInterface and a default implementation TableGateway.

Imagine now that I want a table with a cache for the last queries. I can achive this with the Decorator pattern, creating a CachedTableGateway that depends on TableGateway and a cache component, let's say CacheInterface.

I don't need the cache, but it could be useful.

Should I embed this decorated implementation into the original package, creating a requirement to the cache component? Or should I create an "integration package" that requires both cache and table gateway?

Answer 1

If you are using the Decorator pattern, the CachedTableGateway package would implement the TableGatewayInterface and accept another TableGatewayInterface to forward the requests to that couldn't be found in the cache.

If you have a generic caching package, then the CachedTableGateway package could be implemented using that caching package and that naturally implies a 'requires' relationship between the packages.

Other than that they both implement the same interface, there is no relation between CachedTableGateway and TableGateway. It is up to the client code (which could include integration tests) to decorate a TableGateway with a CachedTableGateway.