The optional elements of a control key give the user the option of posting or not posting certain elements in a primary table. This option, however, does not mean that users always have a choice of posting optional elements. Policy may prevent some of the optional elements from being posted. For example, the Appropriation table is used to monitor appropriation budgets at the level specified by the appropriation bill and by law. Consequently, the posting rules for the Appropriation table are defined by the appropriation bill and other legislation, not by the user.
Some primary tables do, in fact, give users a choice of which optional elements they want to post.
For example, users may customize all optional elements for the Agency Budget table to fit the needs of their agencies. Each primary table in USAS has a different set of required and optional elements in its control key. For example, the control key of the Appropriation table is composed of nine elements-five required and four optional. By comparison, the control key for the Cash Control table posts eight elements-three required and five optional. The next section outlines the required and optional elements for five of USAS's eight primary tables.