provides an integrated toolset for rapidly representing, building, and executing models of critical aspects of complex systems." Requirements Engineering Environment is currently used by the United States Air Force to develop systems. It is: an integrated set of tools that allows systems analysts to rapidly build functional, user interface, and performance prototype models of system components. These modeling activities are performed to gain a greater understanding of complex systems and lessen the impact that inaccurate requirement specifications have on cost and scheduling during the system development process. Models can be constructed easily, and at varying levels of abstraction or granularity, depending on the specific behavioral aspects of the model being exercised. REE is composed of three parts. The first, called proto is a CASE tool specifically designed to support rapid prototyping. The second part is called the Rapid Interface Prototyping System or RIP, which is a collection of tools that facilitate the creation of user interfaces. The third part of REE is a user interface to RIP and proto that is graphical and intended to be easy to use. Rome Laboratory, the developer of REE, intended that to support their internal requirements gathering methodology. Their method has three main parts: Elicitation from various sources (users, interfaces to other systems), specification, and consistency checking Analysis that the needs of diverse users taken together do not conflict and are technically and economically feasible Validation that requirements so derived are an accurate reflection of user needs. In 1996, Rome Labs contracted Software Productivity Solutions (SPS) to further enhance REE to create "a commercial quality REE that supports requirements specification, simulation, user interface prototyping, mapping of requirements to hardware architectures, and code generation..." This system is named the Advanced Requirements Engineering Workstation or AREW. Non-relational environments Non-relational definition of data (e.g. using Caché or associative models) can help make end-user prototyping more productive by delaying or avoiding the need to normalize data at every iteration of a simulation. This may yield earlier/greater clarity of business requirements, though it does not specifically confirm that requirements are technically and economically feasible in the target production system. PSDL PSDL is a prototype description language to describe real-time software. The associated tool set is CAPS (Computer Aided Prototyping System). Prototyping software systems with hard real-time requirements is challenging because timing constraints introduce implementation and hardware dependencies. PSDL addresses these issues by introducing control abstractions that include declarative timing