Special features of precedence network charts

A special feature in both arrow and precedence network diagrams is that of hammock activities. They are used to represent work elements of (initially) unknown duration, such as the need for a piece of equipment to be present while other activities are going to make use of it. Hammocks provide added flexibility during the construction of network diagrams, although the project management literature does not provide any solid rules for the timing of them. Consequently, a review of a number of project scheduling software packages revealed that hammocks are treated superficially, something that may result in severe distortions of the timing of a project. This paper proposes a rigorous algorithm that makes hammocks comply with the ‘behaviour’ of the path they belong to, leaving the rest of the network timing and the resulting bar charts totally unaffected. The implementation of the algorithm in a computer application is also presented.