The Power of Abstraction

Barbara Liskov, MIT, Stanford graduate

Addressing Complexity

Programming Methodology

• How should programs be designed ?
• How should programs be structured ?

The landscape

• E. W. Dijkstra. Go to statement considered harmful. 1968.
• N. Wirth. Program Development by Stepwise Refinement. Cacm, April 1971.
• D.L. Parnas. Information distribution aspect of Design Methodology.

Modularity

• A program is a collection of modules.
• Each has an interface described by specification plus implementation.
• A module's implementation is correct if it meets the specification.
• A using module depends only on the specification.

Benefits

• local reasoning
• modifiability
• independent development

Situation in 1970

Procedures were the only type of module

Partitions to ADT

• Hierarchical Program Structures.
• J.H. Morris. Protection in Programming Languages, Cacm. Jan 1973.
• B. Liskov. Programming with Abstract Data Types. ACM Sigplan Conference on Very High Level Languages. April 1974.
• Objects, operations

From ADTs to CLU

• Static type checking
• Heap based
• Seperation compilation
• No concurrency, no gotos, no inheritance.