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UCT BSA M7 U2: The Functional Decomposition Diagram
Transcript of UCT BSA M7 U2: The Functional Decomposition Diagram
“What components does a fast-food drive-through system consist of?
The first layer of components
The connection between the components:
Notice that there are no arrowheads on these lines connecting the parent and child components.
This is because the connections do not represent the flow of events or how the processes or functions are performed. The diagram and the connections merely represent the relationship between two functions. All these connections signify that the parent component is made up of (and therefore is equal to the sum of) its child parts.
The first layer is made up of the second layer, which is in turn made up of the third layer. That is, the first layer is equal to the sum of the parts in the second layer, which is equal to the sum of the parts in the third layer.
It is important to note that even though the components in this example
seem to be ordered from the start to the end of the process ("Take Order",
"Prepare Order", "Take Payment", then "Deliver Order"), this is not the
purpose of this diagram.
The main purpose of a functional decomposition diagram is to
break down the system into smaller, more manageable and
easily understood functions and tasks.
In this diagram there are four child components, “Take Order”,
“Prepare Order”, “Take Payment”, and “Deliver Order”. These child
components can also be broken down further, and hence be parents to
their own sub-components.
The order of the components could be completely reversed (that is,
“Deliver Order”, Take Payment”, “Prepare Order”, then “Take Order”),
and the diagram would still be correct. What matters is that all of the components are decomposed in the diagram.
It is up to you or your team to decide which layout will suit the system’s functionality that is being decomposed. Remember that the main aim is to provide an uncluttered and clear diagram that contains all the functions
and associated tasks within the system.
If necessary, you could further decompose these components until all the
functions and tasks of a system have been captured. These would become the third and fourth and subsequent layers in your diagram. For example, the parent component "Take payment" has four child components and will, therefore, have four layers. Depending on the nature of the system that you are decomposing, you might need to create multiple pages for more complex or larger systems.
Note that this diagram does not show how the process is performed, or
illustrate the sequence of events. It only shows what is performed by each
function and, collectively in the whole diagram, the system’s
Order of components
The second layer of components:
This layer, like the one before it, will involve at least two child components for each of the
parent components from the layer above. As you go further down from the top layer, the
more detailed the components become. For example, the "Take Order" parent component from layer one has two child sub-components: “Take order from customer”
and “Input order”, while the "Prepare Order" parent component has three child components: "Prepare hot foods", "Prepare drinks" and "Place in bag".
The system to be decomposed
Functional decomposition is the process of breaking down complex or large systems into smaller subparts. Each part of the system is broken down into smaller parts that are more manageable and understandable.
A functional decomposition diagram is a top-down, hierarchical representation of a system’s functionality decomposed into its sub-components. It is important to note that the diagram represents intangible “services” that are an abstraction of a thing that will be delivered and not the thing itself. Functional decomposition diagrams are an essential planning tool.
The system being decomposed in this example is a fast-food drive-through. This main component will need to
be drilled down into at least two sub-components, known as child components. These sub-components will
provide more detail about the parent component that is being broken down. Remember, these provide a
breakdown of the functions and tasks involved in a fast-food drive-through.
Connectors link each function with each of its subordinate sub-functions. Connectors do not connect "sibling" functions.