1.   A search space is a labelled directed graph.

2.   The ARPA project of the mid-seventies relied heavily on the use of domain-specific syntactic and semantic knowledge to constrain the search space.

3.   We can represent this as a three-dimensional search space.

4.   We can view the space of possibilities at the lexical access level as a horizontal slice through the search space, representing a graph of word hypotheses.

5.   By concentrating on the kind of search space produced during lexical access, we provide a way of analysing the interactions between these sources of complexity.

6.   The search space is of a manageable size because TRACE II has a small lexicon and short test utterances.

7.   Was the rapid expansion of the search space due to the nature of speech itself, or to our limited understanding of speech processing?

8.   However the explosion of hypotheses forced the designers to devise various strategies that focused on just some subset of the search space.

9.   Even with such constraints the systems still generated too many partial solutions and had to devise scoring methods and control strategies to prune the search space further.