To generate with a systemic grammar, a choice must be made in each disjunctive choice system during grammar network traversal. In SFG theory, these choices are made implicitly by speakers in order to express their communicative intent, but for a computational implementation an explicit formalization of the choice mechanism is necessary. For Penman, Mann developed the inquiry semantics or chooser/inquiry interface [Mann 1983].
Each choice system has an associated procedure called its chooser, which traverses a decision tree from its root to a single leaf node. The leaf nodes of the tree are the possible choices, and the geometry of the tree is arranged so that the branching nodes are simple binary decisions. Each branching node has an associated inquiry, which obtains information from the external environment in which the grammar is embedded. The chooser then selects which branch to take according to the reponse to the inquiry (see Figure 2.1, from [Matthiessen & Bateman 1991]).
Figure 2.1 shows the contrast between the grammatical terminology (``indicative''/``imperative'') used in the labels on the system networks and the functional terminology (``command?'') used in the inquiries raised by the choosers. This contrast is discussed further in the description of the COMMUNAL project in Section 2.3.1.
The applicability of the inquiry semantics approach to multilingual generation and export machine translation is discussed later in Section 4.4.