What is the best application workflow metaphor for Drupal module? In PHP frameworks we think MVC-style. How do we think inside Drupal?

Asumming I am writing some user-oriented module like Shop, Catalog or Forum. As far as I understand there are no or few MVC based modules. Should I generally treat Drupal modules (as sub-application) as a number of screens connected via forms and hyperlinks or there is a better way.

My question may be a little bit speculative, but I hope someone will share my intent to think models, not just "scripts".

web-applications drupal module
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