2594	 Structured Data Structures	 Programming systems which permit arbitrary linked list structures enable the user to create complicated structures without sufficient protection. Deletions can result in unreachable data elements and there is no guarantee that additions will be performed properly. To remedy this situation this paper proposes a gauge which provides for the creation of a restricted class of data structures but ensures the correctness of the program. This is accomplished by an explicit structure declaration facility a restriction on the permissible operations and execution-time checks. structured programming data structures data base management system
