and their graphic representation vary from implementation to implementation, depending on 1 he character set of a particular computer system. 

Another ordinal type that may llc defined is a subrange of any basic ordinal type (the host type) by indic .lting the smallest and largest values in the interval of values represented by the subrange. 

The structured types are defined by describing the types of their components and by indicating a structuring method. The various structuring methods differ in the mechanism serving to access the components of a variable of the structured type. In Pascal, there are four basic structuring methods available: array structure, record structure, set structure, and file structure. 

In an array structure, all COlli ponents are of the same type. A component is accessed by a complltahle index, whose type is indicated in the array type description and which must be ordinal. It is usually an enumerated type or a subrange of Integer. Given a value of the index type, an indexed variable accesse .. one component of the array. Each array variable can therefore be regarded as a mapping of the index type onto the component type. The time needed for a component access does not depend on the value of the index. The array structure is therefore called a random-access structure. 

In a record structure, the mmponents (called fields) are not necessarily of the same type. In order that the type of a field be evident from the program text (without e\ccuting the program), a field is not specified by a computable value, hut instead is specified by a unique identifier. These field identifier I, are declared in the record type description. Again, the time need,'d 10 access any component does not depend on the field identifier, ,lnd the record is therefore also a random-access structure. 

A record type may be specif 11,:d as having several variants. This implies that different variables, <,:though said to be of the same type, may assume structures that diffel in a certain manner. The difference may consist of a different numbel and different types of components. The variant that is assumed by till: current value of a record variable may be indicated by a component field which is common to all variants and is called the tag field. Usually. the part common to all variants will consist of several components, including the tag field. 

