Further Structured Data Types

Abstract

In the previous chapter, we introduced a VDM composite object, which is the basic mechanism for giving a well-defined structure to a data object. We used composite objects to represent simple record type structures that could be associated together in sets. We implemented these sets in code as linked lists. It is possible to make explicit the linking together of a series of composite objects in the form of a list or a binary tree. We do this by specifying such objects in a recursive manner. We will examine this in the first part of this chapter. In the second part we shall introduce the VDM sequence type, a very useful form of data structure which encapsulates the common programming notion of a list of items without having to resort to the kind of recursive specification which will be described in part one.