Setting the boundaries correctly has crucial importance in the sizing process. It affects the product size (both functional and non-functional), hence it influences effort estimation and the Key Performance Indicators (KPIs) of those sizing units. The setting of the boundary is influenced by the purpose of counting. Therefore, different guidelines should be applied for each sizing purpose.
The purpose of this document is, in part, to guide users of the International Function Point Users Group (IFPUG) functional and non-functional sizing methodologies how to set the boundary and partitions correctly; a partition is a non-functional subdivision of a boundary (to be discussed more fully later). It supports the IFPUG Function Point Counting Practice Manual (CPM) for IFPUG function points (FP), the IFPUG Software Non-functional Assessment Process (SNAP) Assessment Practices Manual (APM) for IFPUG SNAP points (SP) and Simple Function Point Counting Practices Manual for IFPUG Simple Function Points (SFP).
FPs were created to put the business and its needs at the center of the sizing process, displacing technical considerations. The focus is on the measurement of information functions delivered, not on the technical implementation. This approach keeps the sizing method consistent, repeatable (achieving the same results by different sizing experts), and independent of commercial forces.
The same boundary rules and guidelines apply to FP analysis, SNAP, and SFP. SNAP and SFP use the same boundary as used for the functional sizing. Setting the partitions in SNAP depends on how the boundaries are set.
Proper placement of boundaries and partitions has important relevance in applications sizing.
Setting the boundaries defines the interfaces between the analyzed software and its users. This affects the number and the sizes of its transactional functions and data functions. Shifting the positioning of the boundaries changes the counted size regardless of the functionality that is developed.
According to the CPM, the purpose of the count influences the boundary (CPM 4.3.1 Part 2, page 5-2). Counting the same system, but for different purposes, may change the counted size. Therefore, the purpose of the count must be agreed upon and well-documented. It is also important to understand that the sum of the FPs of various applications does not necessarily equal the size of the system that contains these applications. This can happen if the sizing of the system and the sizing of its applications is not done for the exact same purpose. This will also be discussed further later.