MDSD starts with system decomposition, that is, the division of a system into elements in order to improve comprehension of the system and the way in which it meets the needs of the user. Because of the limited capability of humans to understand complexity, a divide and conquer system decomposition approach is appropriate.7 In this approach, the system is decomposed into a comprehensible set of elements, each of which has a comprehensible set of requirements. Sometimes, to manage complexity in very large systems, system decomposition must be applied recursively.
Effective application of system decomposition requires the means of modeling the system from a variety of viewpoints and at increasing levels of specificity. In addition, a set of transformations between model levels is required as a basis of the development process. These transformations provide a means of deriving the next level of specificity while maintaining traceability and coherence for the entire model. MDSD consists of creating the model artifacts as a means of specifying the system elements and their integration. An artifact is defined as any item that describes the architecture, including a diagram, matrix, text document, or the like. This model provides a common means for facilitating collaboration across the engineering disciplines, coordinating iterative development methods, and assigning technical and managerial responsibilities.
System of systems decomposition
In this subsection, we describe a method of object oriented logical decomposition to describe a hierarchical system of systems. Additionally, we discuss a number of principles, found in traditional systems development, that underpin the MDSD framework discussed.
A system encapsulates the resources it requires to deliver its services. Systems can be decomposed into systems, each of which also encapsulates all of their
resources. Because systems control their resources and can encapsulate other systems, a system of systems is a recursive pattern. A process can therefore be
applied to recursively decompose a system into other systems, which are themselves decomposed further. During such recursive decomposition it is
important to understand at which level in the hierarchy we stand during a discussion. Although terms such as superordinate system and subordinate
system are relevant when discussing the pattern, it is sometimes more useful to discuss system levels because more than two levels can be considered.
The term system level indicates the relative position in the overall hierarchy: System level 1 represents the root system (by definition, there is always exactly one system level 1 system). An overview of the key artifacts in two system levels is shown in Figure
7B. Blanchard and W. Fabrycky, Systems Engineering and Analysis, 3rd Edition, Prentice Hall, 1998
Chapter 2. Definitions, design points, and key concepts | 29 |
