The components that make up a system are typically included in the model if they are items that need to be diagnosed, or could be the cause of a failure. These items could be categorized and have certain properties and information attached to them that can be important for troubleshooting.

Many of the components we use in our model can be taken from the parts library. This is a flat list of spare parts that would be required to build or repair the system and contain no information related to their specific function within the system.