The two layers are linked via a command language and a shared set of variables: strings, numbers, or lists. Following any user-generated event, the TCL script sends an appropriate command / argument string to the query layer, which responds by placing appropriate values in a variable accessible from the script. For example, when the user enters the initial query and presses Return, the interface script takes the resulting string from the data entry field and uses it as an argument to the enter parse command. In turn the query layer sends the string to the Okapi search engine and records the resulting data (postings, term weights etc.) as attributes of its own stored objects. It constructs a list of terms in weight order for the interface script, which organises their display in the appropriate area of the interface window.
Other important commands supported by the query layer are to: