In this section I will introduce BUG, a directed bottom up generator, and I will discuss some of its properties. The task for the generator can be seen as follows. The generator will receive a feature structure Top as its input. Part of this feature structure is the semantic structure S_Top. For a given grammar, the generator derives all strings W for which the condition <6> holds (for a formal definition of this concept within LFG cf. Wedekind 1988).
As will become clear in the following paragraphs, a few
conditions on grammars apply for BUG to work properly.
For each grammar rule
there is one daughter that is the semantic head
(specified as such by the rule writer).
For the moment I will assume that if the semantics of the
is instantiated then the semantics of the semantic head
is instantiated too.
I will define the notion 'semantic head' more
precisely in section 2.3.
First I will introduce the basic structure of