The analysis of function and form are interwoven. This chapter is the complement of Chapter 4 and establishes the groundwork for the analysis of function. When employing zigzagging (Section 3.5), the architect works in one domain for a period and then switches to the other. Therefore, discussing form first does not imply any strict sequence in analysis, but rather is a topical organization of material.

Function is less tangible than form, so we begin by defining and describing function in Section 5.2. In Section 5.3, we discuss the externally delivered function that is linked to the primary purpose of the system. This external function emerges from internal functions, as described in Section 5.4. The internal operands create functional interaction and yield the functional architecture (Section 5.5). A system often delivers secondary externally delivered functions as well, and these are discussed in Section 5.6. A short discussion of representing function in SysML concludes the chapter.

In this analysis of function, we will again be guided by a set of questions, given in Table 5.1.