From the client's perspective there are just two types of activities in OGSA-DAI, those that target a resource and those that do not. These correspond to those server-side activities that implement the ResourceActivity extension interfacer and those that don't.

If the activity targets a resource then the client-side activity class must extend:

uk.org.ogsadai.client.toolkit.activity.BaseResourceActivity

If the activity does not target a resource then the client-side activity class must extend:

uk.org.ogsadai.client.toolkit.activity.BaseActivity