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Extending The Concept

The critical path is a core, well proven concept in project management.  However when resource constraints are introduced it is more difficult to specify a distinct critical path.  This series of papers explores how the concept of criticality can be adapted to provide useful information for the management of resource constrained projects.

Criticality in resource constrained networks

Bowers J (1995) Journal of the Operational Research Society Vol.46,pp 80-91.

Project managers readily adopted the concept of the critical path as an aid to identifying those activities most worthy of their attention and possible action.  However, current project management packages do not offer a useful measure of criticality in resource constrained projects.  A revised method of calculating resource constrained float is presented, together with a discussion of its use in project management.  While resource constrained criticality appears to be a practical and useful tool in the analysis of project networks, care is needed in its interpretation as any calculation of such float is conditional on the particular resource allocation employed.  A number of other measures of an activity's importance in a network are described and compared in an application to an aircraft development.  A quantitative comparison of the measures is developed based on a simulation of the process of management identifying the key activities and directing their control efforts.  Resource constrained float appears to be a useful single measure of an activity's importance, encapsulating several useful pieces of management information.  However, there are some circumstances in which other measures might be preferred.

Interpreting float in resource constrained projects

Bowers J (2000) International Journal of Project Management, Vol.18, No.6, pp 385-392.

The concept of float has been adapted for use in resource constrained projects.  However, an important characteristic of such projects is that alternative resource allocations are often possible, resulting in a number of schedules with identical durations.  An activity may be critical in one schedule but have considerable float in another.  Alternative measures of float are explored which capture this flexibility of the resource constrained project.  The practical interpretation of these measures is demonstrated in an analysis of a simplified software development programme.

Multiple schedules and measures of resource constrained float

Bowers J (2000) Journal of the Operational Research Society, Vol.51 No.7 ,pp 855-862.

The conventional analysis of a resource constrained network produces a single schedule. A measure of float for each activity can be defined by examining the sequences of activities, incorporating the linkages implied by the sharing of resources in this particular schedule.  However, the resultant floats are specific to one schedule and the analysis ignores the flexibility inherent in many resource constrained networks.  It is often possible to employ alternative resource allocations resulting in schedules with identical overall durations but different timings for individual activities; in one schedule an activity may be critical but in another it may have significant float.  A systematic exploration of alternative schedules reveals the flexibility of the network and the consequent variation in activities’ floats.  The paper defines new parameters describing these characteristics of activities in resource constrained networks.  The practical value of the parameters is demonstrated in an example in which the measures of float guide the project planner to an alternative schedule, avoiding a critical dependency on a problematic activity and reducing the risk to the project at no additional cost.

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