Defined Data Types Research Articles

The programming language PASCAL

In Part 1, the structure of a PASCAL program as a collection of declarations and statements was laid out. This part begins with a description of PASCAL's unique facilities for defining data types to suit a particular problem. Statements, the sequences of reserved words, identifiers and symbols that specify the actions in a PASCAL program, are then described.

String storage and searching for data base applications

User and hardware cost trends dictate that data base systems should provide more complete functionality, simplicity of use, and reliability by increasing the amount of hardware present in the system. These goals are accomplished with a simple hardware arrangement within a one-dimensional cellular storage system called INDY. The INDY backend kernel is intended as a powerful tool for implementing all data models. The INDY cellular storage array is intended to provide functionality that is difficult to implement efficiently using a conventional hardware arrangement. It allows a simple implementation of improved data independence at high speeds. INDY simultaneously satisfies the time windows of future hardware technologies and user requirements.The importance of strings as a mechanism for defining abstract data types for data base languages is discussed in more detail in another paper. In that paper, a language called STRING is introduced which allows names of data objects to be semantically defined as variable-length strings and compared based on string pattern membership. This paper is concerned with the implementation of string storage and searching required by the STRING language. Implementation of higher level structures and searching requirements (such as sets, rows, tables and hierarchies) on the INDY kernel is treated elsewhere.

String storage and searching for data base applications

User and hardware cost trends dictate that data base systems should provide more complete functionality, simplicity of use, and reliability by increasing the amount of hardware present in the system. These goals are accomplished with a simple hardware arrangement within a one-dimensional cellular storage system called INDY. The INDY backend kernel is intended as a powerful tool for implementing all data models. The INDY cellular storage array is intended to provide functionality that is difficult to implement efficiently using a conventional hardware arrangement. It allows a simple implementation of improved data independence at high speeds. INDY simultaneously satisfies the time windows of future hardware technologies and user requirements.The importance of strings as a mechanism for defining abstract data types for data base languages is discussed in more detail in another paper. In that paper, a language called STRING is introduced which allows names of data objects to be semantically defined as variable-length strings and compared based on string pattern membership. This paper is concerned with the implementation of string storage and searching required by the STRING language. Implementation of higher level structures and searching requirements (such as sets, rows, tables and hierarchies) on the INDY kernel is treated elsewhere.

String storage and searching for data base applications

User and hardware cost trends dictate that data base systems should provide more complete functionality, simplicity of use, and reliability by increasing the amount of hardware present in the system. These goals are accomplished with a simple hardware arrangement within a one-dimensional cellular storage system called INDY. The INDY backend kernel is intended as a powerful tool for implementing all data models. The INDY cellular storage array is intended to provide functionality that is difficult to implement efficiently using a conventional hardware arrangement. It allows a simple implementation of improved data independence at high speeds. INDY simultaneously satisfies the time windows of future hardware technologies and user requirements.The importance of strings as a mechanism for defining abstract data types for data base languages is discussed in more detail in another paper. In that paper, a language called STRING is introduced which allows names of data objects to be semantically defined as variable-length strings and compared based on string pattern membership. This paper is concerned with the implementation of string storage and searching required by the STRING language. Implementation of higher level structures and searching requirements (such as sets, rows, tables and hierarchies) on the INDY kernel is treated elsewhere.

Abstract types defined as classes of variables

The concept of “type” has been used without a precise definition in discussions about programming languages for 20 years. Before the concept of user defined data types was introduced, a definition was not necessary for discussions of specific programming languages. The meaning of the term was implicit in the small list of possible types supported by the language. There was even enough similarity between different languages so that this form of definition allowed discussions of languages in general. The need for a widely accepted definition of type became clear in discussions of languages that allow users to add to the set of possible types without altering the compiler. In such languages, the concept of type is no longer implicitly defined by the set of built-in types. A consistent language must be based on a clearer definition of the notion of type than we now have.

Abstract types defined as classes of variables

The concept of “type” has been used without a precise definition in discussions about programming languages for 20 years. Before the concept of user defined data types was introduced, a definition was not necessary for discussions of specific programming languages. The meaning of the term was implicit in the small list of possible types supported by the language. There was even enough similarity between different languages so that this form of definition allowed discussions of languages in general. The need for a widely accepted definition of type became clear in discussions of languages that allow users to add to the set of possible types without altering the compiler. In such languages, the concept of type is no longer implicitly defined by the set of built-in types. A consistent language must be based on a clearer definition of the notion of type than we now have.

Programming without pointer variables

The presence of pointer variables in high level programming languages constitutes an artifact originally introduced to support the representation of recursive data structures. Programming practice has come to rely on pointer variables for their originally intended use, and for several others as well. Their use adds to the complexity of stating algorithms by forcing one to conceptualize data representations in which storage addressing is made manifest. In addition, the use of pointer variables allows one to refer to a common data object by a multiplicity of names, a phenomenon we call the alias variable problem, Alias variables make the verification of program behavior substanially more difficult, and frustrate the goals of modular decomposition. In this paper, we consider alternatives to the use of pointer variables in programming. One of these alternatives is the inclusion of a class of data abstractions based on recursively defined data types. The representational power of the proposed data types is characterized formally, and some issues of implementation and efficiency of programs are discussed.

Programming without pointer variables

The presence of pointer variables in high level programming languages constitutes an artifact originally introduced to support the representation of recursive data structures. Programming practice has come to rely on pointer variables for their originally intended use, and for several others as well. Their use adds to the complexity of stating algorithms by forcing one to conceptualize data representations in which storage addressing is made manifest. In addition, the use of pointer variables allows one to refer to a common data object by a multiplicity of names, a phenomenon we call the alias variable problem, Alias variables make the verification of program behavior substanially more difficult, and frustrate the goals of modular decomposition. In this paper, we consider alternatives to the use of pointer variables in programming. One of these alternatives is the inclusion of a class of data abstractions based on recursively defined data types. The representational power of the proposed data types is characterized formally, and some issues of implementation and efficiency of programs are discussed.