The earlier XOkapi GUI (see 1.4.2 above) was defined using the Motif UIL (User Interface Language). This proved inflexible, in that the definitions must be compiled along with the rest of the C code implementing the search system. Moreover it handled only Motif widget definition --- any form of optionality or user-level flow of control had to be built into the underlying C code.
The tool selected for the ENQUIRE project was TCL/TK: a public-domain scripting language and toolkit developed by John Ousterhout [6]. TCL is an interpreted command language which provides a high level of flexibility. An interface built with TCL can be changed rapidly, even while the application is running, so contributing towards the important goal of configurability. At the same time TCL can communicate with programs written in a compiled language like C++, so that it is possible to perform the functions making up the overall system at the most appropriate level.