In this paper, we consider a way of bridging informal and formal
specification.  Most projects have a need for an informal description
of the requirements of the system which all people involved can
understand.  At the same time, there is a need to make some of the
requirements more formal. We present a way to relate informal
requirements, in form of use cases, to more formal specifications, 
written in the Object Constraint Language (OCL). Our
approach gives the customers of software systems a way of guiding the
development of formal specifications.  Conversely, the formal
specification can improve the informal understanding of the system by
exposing gaps and ambiguities in the informal specification.