What arethe main differences in methodology between "Requirements Engineering" and "Usability Engineering"? Where do they overlap, where not? Which activities are common between the two and which are exclusive?
We have developed over the last few years our own SWE BOK in our company, and there we see the two disciplines like that:
Requirements are seen in our nomenclature like that:
As you can see, usability is part of the non functional requirements.
Personally, I would not separate these out. I spend a lot of time acting as a business analyst for projects, and whenever possible I make sure that usability is part of the main requirements gathering effort. They may be listed in a sub-category, such as "Interface requirements" or "UI requirements" but the end result is the same - a list of expressions of need that are actionable and verifiable.
Again, I see a large part of the efforts as being so intertwined that I don't see value in separating them out. All the usual activities apply:
Edit: I see that mliebelt has posted a different approach; and that's perhaps the most important thing to state here - do what works in the local situation as no two development shops are the same, and so no two approaches will be the same.
I read the two replies by mliebelt and Gray a couple of times. I partially agree with both. It sounds correct to me to define UE as solution-oriented and RE as problem-oriented, but the current studies aim to focus on their intersection.
If we take a look at the recent reference in RE (e.g Alan M. Davi's book: JERM), we see that taking product/solution into account from early stages (i.e. RE) is recommended for developing the right product.
On the other hand, recently, there have been efforts to mix these two concepts, in order to develop products with higher usability. For instance, take a look at "Human-centered software Engineering" by A. Seffah et al. in which the main focus is to bridge the gap between UE and SE.
So I would say, however, previously RE and UE have been treated separately, nowadays, the importance of including usability requirements (and consequently some usability-related activities, i.e UE) in RE activities is being acknowledged. In particular, activities in UE that lead to creation of Usability specification. I still think usability evaluation is not part of RE by nature.