Survey of Model-Based Systems Engineering (MBSE) Methodologies

2. Differentiating Methodologies from Processes, Methods, and Lifecycle Models

In order to better understand key features of the various leading MBSE methodologies surveyed in this study, it is critically important to establish the terminology associated with processes, methods, and methodology, and to acknowledge the myriad lifecycle models used in the acquisition and development of large-scale, complex systems. Without such grounding, it will be extremely difficult to map any assessment and selection of candidate MBSE methodologies into the fabric of the systems engineering environment within a particular organization.

2.1 Process, Method, Tool, Methodology, and Environment Defined The word methodology is often erroneously considered synonymous with the word process. For purposes of this study, the following definitions from Martin [2] are used to distinguish methodology from process, methods, and tools:
• A Process (P) is a logical sequence of tasks performed to achieve a particular objective. A process defines “WHAT” is to be done, without specifying “HOW” each task is performed. The structure of a process provides several levels of aggregation to allow analysis an definition to be done at various levels of detail to support different decision-making needs.
• A Process (P) is a logical sequence of tasks performed to achieve a particular objective.A Method (M) consists of techniques for performing a task, in other words, it defines the “HOW” of each task. (In this context, the words “method,” “technique,” “practice,” and “procedure” are often used interchangeably.) At any level, process tasks are performed using methods. However, each method is also a process itself, with a sequence of tasks to be performed for that particular method. In other words, the “HOW” at one level of abstraction becomes the “WHAT” at the next lower level.
• A Tool (T) is an instrument that, when applied to a particular method, can enhance the efficiency of the task; provided it is applied properly and by somebody with proper skills and training. The purpose of a tool should be to facilitate the accomplishment of the “HOWs.” In a broader sense, a tool enhances the “WHAT” and the “HOW.” Most tool used to support systems engineering are computer- or software-based, which also known as Computer Aided Engineering (CAE) tools.