6.3 Suspended Ceiling Design Process - Bilkent University

3.2.1 Network Models
Network models can overcome some of the drawbacks of generic
models by exploiting activity relationships. Such models are based on
the premise that once decomposed, the design process can be
described as an interconnected network of design tasks i.e. a directed
graph. A directed graph (digraph) represents the precedence
relationships among tasks of a project. It consists of a set of nodes
representing the design tasks and a set of directed lines connecting
these nodes. The directed lines denote a dependency or a relationship
between the connected tasks (Yassine et al., 1999). There are many
variations of network models, but only the four basic types are
discussed below.
3.2.1.1 PERT/CPM
The Project Evaluation and Review Technique (PERT) and the Critical
Path Method (CPM) are based on digraphs. The PERT method is the
first example of time-based process modeling. In the PERT method,
three probabilistic time estimates are given to each task, reflecting the
uncertainty in the duration of tasks. The CPM is a variation of the PERT
method. However, the time of any task can be compressed by allocating
resources. Thus, CPM assumes a time-cost tradeoff rather than the
probabilistic times used in PERT. CPM diagrams also graphically show
the precedence interrelationships among product activities. It is possible
to develop a critical path −a sequence of activities which, if delayed,
delays completion of the project− (Smith and Morrow, 1999).
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