Functions
The functionality in each Functional Area is decomposed into several Functions that form a hierarchical set of High-level and Low-level Functions.
Low-level Functions contain simple (un-complex) functionality which is easy to describe, and thus contain the lowest level of functionality in each Functional Area. The Functional Requirements provide details of what the Functions actually do with the data that they receive in order to produce the data that they send out.
High-level Functions are groups of Low-level Functions. They are used to represent these Low-level Functions at higher levels in the hierarchy in order to make it easier to understand the overall functionality within a Functional Area.
Each Function has a number and a name. The numbers are used to identify the position of each Function in the hierarchy within each Functional Area, whilst the names are a simplified expression of what the Function does.