The document discusses characteristics of good software design including component independence, high cohesion, and low coupling. It defines different types of coupling (content, common, control, stamp, data) and cohesion (coincidental, logical, temporal, procedural, communicational, functional). Examples are provided to illustrate each type of coupling and cohesion. Maintaining low coupling and high cohesion results in components that are easier to understand, modify, and reuse.

1. Coupling and Cohesion Pfleeger, S., Software Engineering Theory and Practice. Prentice Hall, 2001.

3. Coupling: Degree of dependence among components No dependencies Loosely coupled-some dependencies Highly coupled-many dependencies High coupling makes modifying parts of the system difficult, e.g., modifying a component affects all the components to which the component is connected.

4. Range of Coupling High Coupling Loose Low Content Common Control Stamp Data Uncoupled

19. Range of Cohesion High Cohesion Low Functional Informational Sequential Communicational Procedural Temporal Logical Coincidental

35. Examples of Cohesion-1 Function A Function B Function D Function C Function E Coincidental Parts unrelated Function A Function A’ Function A’’ logic Logical Similar functions Time t 0 Time t 0 + X Time t 0 + 2X Temporal Related by time Function A Function B Function C Procedural Related by order of functions

36. Examples of Cohesion-2 Function A part 1 Function A part 2 Function A part 3 Functional Sequential with complete, related functions Function A Function B Function C Communicational Access same data Function A Function B Function C Sequential Output of one is input to another

37. p q t r s u 1 2 3 4 5 6 No. In Out Interface Description p, t, u access the same database in update mode Problem: Define coupling between pairs of modules. 1 Aircraft type Status flag 2 ----- List of aircraft parts 3 Function code ----- 4 ----- List of aircraft parts 5 Part number Part manufacturer 6 Part number Part name

38. Coupling between pairs of modules q r s t u p q --- --- r --- --- s --- t