A behavioral notion of subtyping

The use of hierarchy is an important component of object-oriented design. Hierarchy allows the use of type families, in which higher level supertypes capture the behavior that all of their subtypes have in common. For this methodology to be effective, it is necessary to have a clear understanding of...

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Bibliographic Details
Published in:ACM transactions on programming languages and systems 1994-11, Vol.16 (6), p.1811-1841
Main Authors: Liskov, Barbara H., Wing, Jeannette M.
Format: Article
Language:English
Subjects:
General programming languages
Invariants
Language types
Object oriented languages
Pre- and post-conditions
Program constructs
Program reasoning
Program specifications
Semantics and reasoning
Software and its engineering
Software creation and management
Software development methods
Software development process management
Software notations and tools
Specification languages
System description languages
Theory of computation
Type structures
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Summary:The use of hierarchy is an important component of object-oriented design. Hierarchy allows the use of type families, in which higher level supertypes capture the behavior that all of their subtypes have in common. For this methodology to be effective, it is necessary to have a clear understanding of how subtypes and supertypes are related. This paper takes the position that the relationship should ensure that any property proved about supertype objects also holds for its subtype objects. It presents two ways of defining the subtype relation, each of which meets this criterion, and each of which is easy for programmers to use. The subtype relation is based on the specifications of the sub- and supertypes; the paper presents a way of specifying types that makes it convenient to define the subtype relation. The paper also discusses the ramifications of this notion of subtyping on the design of type families.
ISSN:0164-0925
1558-4593
DOI:10.1145/197320.197383