The case-based subsystem is the AI component of the system
that operates Pon the KB, analyzing the current context in order
to retrieve and suggest new letters to users. It is composed of
two main components: the case library (CL) and the case-based
reasoner (CBR). The former is a KB repository of previously instantiated
letters, while the CBR is the engine that performs the casebased
reasoning process [1]. In particular, the main purpose of
the CBR is to manage the CL, storing and retrieving, on-demand,
new letter instances. Before discussing the CBR component, we
give a formalization of the variables used by the reasoner for the
CL analysis.