The approach to representation and presentation of knowledge used in ARIES, an environment to experiment with support for analysts in modeling target domains and in entering and formalizing system requirements, is described. To effectively do this, ARIES must manage a variety of notations so that analysts can enter information in a natural manner, and ARIES can present it back in different notations and from different viewpoints. To provide this functionality, a single, highly expressive internal representation is used for all information in the system. The system architecture separates representation and presentation, in order to localize consistency and propagation issues. The presentation architecture is tailored to be flexible enough so that new notations can be easily introduced on top of the underlying representation. Presentation knowledge is coupled to specification evolution knowledge thereby leveraging common representations for both in order to provide automated focusing support to users who need informative guidance in creating and modifying specifications.>