A B-tree 21 is used to store natural language data, for example as part of a speech recognition or speech synthesis system. The B-tree is arranged in a hierarchy, with each node pointing to two nodes in the level below. Each node contains a test value (a word), and data relating to that test value (or a reference to a storage location where the data is maintained). The data is accessed by starting at the top of the tree and comparing the desired word with the test value for that node. Depending on the relative alphabetical ordering of the desired word and the test value, the appropriate branch from that node is followed. This process is continued down the tree until a test value corresponding to the desired word is located. The B-tree is arranged so that frequency of occurrence of the test values in natural language decreases substantially monotonically as the tree is descended. <IMAGE>
Natural language processing system.