The concept of relevance tree, one of the normative methods, was first described –by C.W. Churchman et akin 1957. In this method the objective to- be achieved is divided into a set of major activities. Each activity is broken down farther into missions and each mission is subdivided into a task.
Then the deficiency with respect to the specific task is identified based on which a project or an action is recommended. It thus involves a hierarchical listing of tasks as well as its alternatives and each branch is thus to be considered as a goal ; sub-goal etc. The main advantage of the method is that the objectives and the actions to be taken get linked.
A relevance tree is shown in Figure-1. Relevance tree enables the planner to assess systematically all the interlinked technologies and tasks which could lead to the achievement of an objective. We can then select the most appropriate path to do so.
The method consists of the following steps
Step 1 : Arrange in hierarchical order the objectives, sub objectives, activities, 20 missions or tasks.
Step 2 : Ensure that all possible ways of achieving the objectives have been included or assessed:
Step 3: Evaluate the relevance of individual tasks and sub-objectives to the overall objectives.
The relevance tree technique serves as a tool both for forecasting and planning process.
Figure-1 : Relevance Tree
Relevance tree technique not only determines and evaluates systematically the alternative paths through which a normative objective or a mission could be accomplished, but also provides an insight into problems that have to be surmounted to achieve a goal. Many R&D type problems are amenable to such analysis by means of a “Problem Relevance Tree” analysis. Figure-2 below depicts such a situation for development of a Solar Car which has potential to provide a pollution free mode of road transport.
Figure-2 : Problem Relevance Tree
In this case, we are attempting to examine the issues of designing a solar car by considering the major problems that are to be solved in the sub-systems and sub-subsystems, and so on. It is important that all the technological problems emanating from a node must be solved before the predetermined goals for that node are achieved and thereby enabling us to design the solar car finally.
You should try to build such relevance trees for specific technologies/ products you are familiar with. While doing so you will realise the need of arriving at/deciding the quantum of inputs required at different branches to reach a node. This quantitative judgement is essential since the decision maker, based on these estimates, would allocate resources in terms of men; materials and money, commensurate with the importance of the task/activity for solution of a problem. To analyse the problem rationally, a scheme of applying “relevance numbers” to each branch of relevance tree was developed at Honeywell. Figure 4.6 illustrates a relevance tree with relevance numbers. To cover all possibilities the tree must have an exhaustive listing of all the alternatives. There should not be any overlap between the branches at one node to ensure that alternatives are mutually exclusive.
The objective `O’ can be achieved by completing all the three tasks, Ti, T2 and T3, (Figure-3). Each task can be assigned a relevance number proportional to the relative importance of the task in achieving the objective. Each task can be achieved by one or more approaches. Each approach is assigned a relevance number in turn. For each task and approach the relevance numbers assigned are normalised such that they add up to one. By multiplying the relevance numbers of each task and the approach following a particular path, the relevance number of each path can be obtained. The relevance numbers so obtained and shown in the boxes under each approach indicate the relative inputs required for each path to achieve the objective.
Figure – 3 : Relevance Numbers
Relevance tree is a powerful and general-technique with a wide range of applicability. It can be used for identifying new system alternatives and this can be a technique for obtaining divergent solutions to a given problem, or for obtaining a convergence for integrating many of the subsystems.
ADVANTAGES AND DISADVANTAGES
a) provides a systematic method for assessing the route to be used for achieving a defined future objective or solving a given problem,
b) helps in deciding whether an objective is likely to be achieved or not,
c) `helps in determining alternative ways by which a given objective might be achieved,
d) establishes the need for carrying out detailed technological forecasts of critical tasks/approaches that are to be achieved in a given time scale,
e) ensures that adequate and appropriate attention is applied to all tasks and activities depending on-their relevance,
The relevance tree for a large complex technology could become too complicated to be handled.