Principle 1: The information domain of a problem must be represented and understood. The information domain encompasses the data that flow into the system, the data that flow out of the system, and the data stores that collect and organize persistent data objects.
Principle 2: The functions that the software performs must be defined. Software functions provide direct benefit to end users and also provide internal support for those features that are user visible. Some functions transform data that flow into the system. In other cases, functions affect some level of control over internal software processing or external system elements. Functions can be described at many different levels of abstraction, ranging from a general statement of purpose to a detailed description of the processing elements that must be invoked.
Principle 3: The behavior of the software (as a consequence of external events) must be represented. The behavior of computer software is driven by its interaction with the external environment. Input provided by end users, control data provided by an external system, or monitoring data collected over a network all cause the software to behave in a specific way.
Principle 4: The models that depict information function and behavior must be partitioned in a manner that uncovers detail in a layered (or hierarchical) fashion. Requirement’s modeling is the first step in software engineering problem solving. It allows you to better understand the problem and establishes a basis for the solution. Complex problems are difficult to solve in their entirety. For this reason, you should use a divide and-conquer strategy. A large, complex problem is divided into sub problems until each sub problem is relatively easy to understand. This concept is called partitioning or separation of concerns, and it is a key strategy in requirements modeling.
Principle 5: The analysis task should move from essential information toward implementation detail. Requirements modeling begin by describing the problem from the end-user ‘s perspective. The essence of the problem is described without any consideration of how a solution will be implemented.
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