Although approaches based on use cases proved to be very effective in requirements capture activity, its lack of formality leaves them far away from the expressions of solution designs for the modeled cases. This lack of formality in the use cases expressions makes the task of deriving solution designs in an ambiguous one, left solely to the wisdom of the analyst/designer. This paper presents a proposal that tries to support the process of deriving solution designs for requirements specifications based on use cases, without resigning the ad-vantages obtained from the informal, close to business expressions that distin-guish these approaches.