MFM Tutorial
An MFM model is a goal-means representation of an enginering artifact, that consist of two parts: 1) A graphical functional representation using flow functions and causal relations of how the artifact works, and which can be used to display results related to goal fulfilment and/or threats, and 2) An underlying rulebased representation, which can be used in a rule engine to reason about the consequences of deviations for goal fulfilment. In scientific papers about MFM usually only the resulting graphical representation is published.
In this tutorial the different graphical symbols for flow functions and causal relations will be explained, and then used to create the graphical part of the functional representation of a crude oil (or other product) storage tank. I the graphical representation of the MFM models is developed either in the editor developed by the Lind Group in collaboration with the Halden Project, or the editor developed by the Norwegian company Eldor, the underlying rulebased representation is created automatically.
Graphical symbols and syntaks used in MFM modelling
The figure to the right shows the basic graphical symbols of MFM flow functions used to create the graphical functional representation. The MFM flow functions are contained in an MFM flow structure, and an MFM graphical functional representation may consist of one or more flow structures. Each flow structure has an objective. Inside the flow structure there can be one or more sources representing the raw materials, and one or more sinks representing the products.
Beside the source and sink flow functions there are 4 more basic flow functions: transport, barrier (opposite of transport), storage and balance. Over the years, as the use of MFM have expanded to different domains additional flow functions have been defined to represent chemical processes, e.g. mixing, conversion, and separation to name the most used ones. The use of these additional flow functions will be demonstrated en a second tutorial. Graphical elements to represent control structures have also been developed.
The flow functions within a flow structure are connected with the agent and participant connectors shown in the figure to the left. Means-end connectors are the two four connectors in the figure to the left. They connect the means in one flow structure - a specific flow function inside the flow structure - to the end in another flowstructure - a specific flow function in another flow structure, representing the purpose of the model or part of the model.
Syntactically there always have to be a transport function between any two of the other flow functions. This means, that the simplest syntactically correct model of our storage tank will consist of five flow functions: a source, a transport, a storage, another transport, and a sink, as shown in the following graphical representation