Metra potential method
The Metra-Potential-Method ( MPM , also called activity-node representation or process-node representation ) is a network plan technique as well as a method of graph theory for the calculation of network plans. It is a very helpful tool for project organization and monitoring or for time management of projects .
history
The Metra-Potential-Method was developed in 1959 by Bernard Roy from the Metra Group, today Atos Origin , and was first used in the construction of a nuclear power plant for Electricité de France , as well as in the construction of the cruise ship France and Concorde . The method was later used in many companies to represent and organize larger projects.
Basics
In MPM network plans, the processes are represented as rectangles (nodes) (process node network plan) and the dependencies between the processes are symbolized by arrows (process node network plan). Milestones that are taken from the work breakdown structure (WBS) , for example , are displayed as activities with a duration of 0.
Fundamental for the preparation of the MPM network plan is that the nodes are associated in accordance with an end-top relationship (the concept relationships see network planning ). Any arrow coming from a knot must end in another knot. The minimum time intervals between two processes are shown by a positive arrow label, the maximum time interval by a negative arrow label. Two processes can therefore be linked by a maximum of two arrows (one positive and one negative). However, this has the consequence that MPM network plans can contain cycles (see: CPM network plans are cycle-free, as no maximum time intervals can be displayed). Since cycles are possible, an MPM network plan does not necessarily have a source or sink (the start or start process can be part of a cycle).
Creation
The planning object of an MPM network plan can either be an entire project or just certain project phases. A network plan can be used as a rough or detailed process and schedule method. A rough network plan is sufficient for an overall project and detailed network plans can be created for individual project phases.
For the creation of network plans, work packages are to be broken down until processes arise for which the following conditions apply: The process is carried out without interruption and the use of resources takes place in constant quantities per time unit.
For the graphical representation, you should decide on a uniform flow direction for the visualization, either consistently from left to right or from top to bottom. When analyzing the dependencies of the individual processes, both technological and non-resource-dependent relationships are decisive. Earlier network plans can be helpful in creating the network plan and serve as a guide.
Next, the durations of the processes must be estimated or measured. Each process has extreme dates, an earliest (possible) start time and the latest (permitted) end time. The dates of the processes are calculated using project management software, but the calculation can also be done manually. The times are always calculated in two steps.
Forward calculation
First, a forward calculation is carried out , in which, based on the starting point of the network plan, the next following, earliest possible start date of an activity is calculated. If an activity has several predecessors, the earliest possible start time of the activity is the earliest end time of the longest previous activity.
Backward calculation
The reverse process is used for the backward calculation. Starting from the end time, the latest start times of these are calculated by subtracting the duration of the previous activities. In this case, care must be taken as soon as the process under consideration has several successors. In this case, the duration of the process must be subtracted from the latest start times of the successors and compared with each other. Here the smallest value must be specified as the latest start time for the process.
Total buffer
If one of the processes has a buffer time , you can vary between the earliest possible start date and the latest possible start date. If the earliest possible and the latest permitted time are the same for a process, the total buffer, which results from the difference between the earliest and latest starting time, is equal to zero. In this case, it is a so-called critical process, in which no delays are allowed.
Free buffer
The free buffer times can also be calculated very easily in an MPM plan . The definition of the free buffer means that all previous activities have been started and completed according to plan, i.e. punctually at the earliest possible point in time, and the subsequent process must not be influenced. In this way, the duration of the process is added to the earliest possible start time of the process and this value is subtracted from the earliest possible start time of the follow-up activity. If the process has several successors, the difference must be determined at all the earliest possible starting times of the successors, as each of the subsequent activities must be free from using the buffer.
Independent buffer
The independent buffer , which, in addition to the specifications of the free buffer, also has the requirement that the previous activities may begin at the latest possible time, can also be easily determined in an MPM plan. The buffer is independent , as it exists if it can be used independently of the predecessors (i.e. the predecessors can also start at the latest possible point in time) and has no impact on the successors (i.e. they may start at the earliest possible point in time).
The independent buffer is therefore calculated from the difference between the earliest possible start time of the successors and the sum of the duration of the activity + the latest start time of the predecessors + duration of the predecessors.
See also
literature
- Neumann / Morlock: Operations Research: with 111 tables . Hanser, Vienna 1993, ISBN 3-446-15771-9
- Zimmermann / Stark / Rieck: Project planning - models, methods, management. Springer, Berlin 2006
Individual evidence
- ^ Ludwig H. Hennicke: Knowledge-based expansion of network technology . In: Werner A. Müller (Hrsg.): Economic contributions . tape 47 . Physica-Verlag Heidelberg, Heidelberg 1991, ISBN 978-3-7908-0544-4 , 4.4.1.2. Metra Potential Method (MPM), p. 41 .