Is there a way of creating a composite field that can have multiple values, with each value having another group of composite values?
E.g. we want to have this structure at the end:
Is this possible at all for a custom module that defines a CCK field? If so, can someone push me in the right direction?
this is a very know and debated issue in the drupal world.
this feature is called cck "multigroup" and it looks it's pretty difficult to implement. there are a lot of posts in the drupal forum about this, i suggest you to start here:
it's a kind of "hidden" feature in the cck module. looking in the module directory, you will find instructions here:
cck/modules/content_multigroup/README.txt
Edit: Ongoing work on the multigroup module has moved to the experimental
CCK 3.0 branch.
in the meantime you can try to deal with it using the flexifield module (but it's kinda hackish, i won't use it in production)