ITPEC FE Morning October 2020 Question 47

Data coupling — modules that exchange only the data they need, as parameters, depend on each other the least.

Coupling measures how strongly modules depend on each other, and weaker is better. From weakest to strongest:

• •Data coupling: only the needed data items are passed as parameters
• •Stamp coupling: a whole data structure is passed although only part of it is used
• •Control coupling: a parameter is a flag that selects the logic inside the called module
• •External coupling: modules share individual global data items
• •Common coupling: modules share a common global data area
• •Content coupling: one module refers to or changes the inside of another directly

Answer (c)

Why not others:

• •(a) Common coupling — modules communicate through a shared global data area, so a change to it affects every module that uses it
• •(b) Control coupling — parameters are used, but one of them is a control flag that steers the called module's logic, so the caller must know how it works inside
• •(d) Content coupling — the strongest kind: one module reaches directly into another's code or data

Key rule: The less a module knows about another's internals and the less data they share, the weaker the coupling: plain parameters beat flags, shared globals and direct access.

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