I am working with a site with a lots of modules.

some of the modules are inter-linked to each-other; such as article and resource, Member and Level.

And now i need to make the modules inter-linked if they exist, and independent if they dont.
its like if we have member module without level, then all the members should be equal. there should not be leveling of the member.

now after few months if the user install level module ... then ... now without any change in member module .. we need to integrate both the modules.

I could not figure out the way to implement this.

Any suggestions will be appreciated

umm..I didn't get what you really want..But as per my understanding, it can be done using sql. Say a user adds a level module. Have a column in the table with name level_module. If the user has installed a level module, set it to 1. You can then check if level_module is 1 for that particular user.

Its coool ... there is no problem in checking the existence of the modules.

I am little bit talking about the cms type modules, that has not defined exact numbers of modules.

i will be distributing the cms to number web hostels.
then on continuous basics i will be developing the new modules like by the drupal/ joomal.

now these modules need to be integrated with that of old existing modules without any modification on old module.

you have an article module. you had put textarea for the description files input.
now Tinymce module can. with a plug-and-play functionality.
if we install the Tinymce module ... it will convert the older textareas to text-editors.
------- this was just an inter component - module compatibility ---------

That's why i want to make the modules inter compatibility form the beginning.