(71) analysis emphasizes the drawing of pictorial system models to document and validate both existing and/or proposed systems. Ultimately, the system models become the (72) for designing and constructing an improved system. (73) is such a technique. The emphasis in this technique is process-centered. Systems analysts draw a series of process models called (74) . (75) is another such technique that integrates data and process concerns into constructs called objects.
（74）处填（）。
A．PERT
B．DFD
C．ERD
D．UML