Generating Project Networks

Procedures for optimization and resource allocation in Operations Research first require a project network for the task to be specified. The specification of a project network is at present done in an intuitive way. AI work in plan formation has developed formalisms for specifying primitive activities, and recent work by Sacerdoti (1975a) has developed a planner able to generate a plan as a partially ordered network of actions. The "planning: a joint AI/OR ap-proach" project at Edinburgh has extended such work and provided a hierarchic planner which can aid in the generation of project networks. This paper describes the planner (NONLIN) and the Task Formalism (TF) used to hierarchically specify a domain. 1. AI and OR approaches to planning The general problem of planning a task is one of very broad scope. Current work in Operations Research (OR) and Artificial Intelligence (AI) has concentrated on different aspects of the problem. We have taken an interdisciplinary approach in the hope that this will lead to a development of both these aspects. In the OR approach, the planning process falls into two stages. 1. The constituent "jobs" of a plan are specified together with their precedence relationships (i.e. requirements of the form that one job precede another). This information defines a graph, termed a project network. 2. Various operations are performed on the project network to establish schedules and allocate resources (e.g. using critical path analysis). OR work has been concerned with the second stage of computational operations on a given project network. The preliminary stage is performed in an intuitive, not well understood, and probably haphazard way. It can be argued that the generation of a project network is important because of the structure it imposes on the task in hand. It forces component jobs to be isolated and necessary order-ings between them considered. The project network can be used not only for predictions of how the project will be done, but also as a tool to aid in monitoring its progress and allowing bottlenecks to be identified. However, a considerable amount of effort is expended in the manual construction of project networks. Steps towards automating the process of specifying constituent jobs for some task and for giving the precedence relationships between jobs, have been developed for representing the data to the planning process, i.e. a description of the goals of the plan and the operations (jobs) of which it might …