Which properties make a modelling notation easy for untrained users to understand?

One of the essential components of interactive development is a model or representation that can be understood by all parties. Although in some development projects this requirement is fulfilled by an early prototype, there are many situations in which paper-based models have to be used. Clients and users are often unfamiliar with notations for modelling software systems and therefore find it difficult to understand models produced using such notations well enough to contribute effectively to the development process. In this paper we identify and discuss properties of modelling notations that contribute to the production of models that untrained users can readily understand.