We develop a formal, type-theoretic account of the basic mechanisms of object-oriented programming: encapsulation, message passing, subtyping, and inheritance. By modeling object encapsulation in terms of existential types instead of the recursive records used in other recent studies, we obtain a substantial simplification both in the model of objects and in the underlying typed -calculus.

We introduce a simple, programming language independent rule (known in-house as the Law of Demeter) which encodes the ideas of encapsulation and modularity in an easy to follow form for the object-oriented programmer. The rule achieves the following related benefits if code duplication, the number of method arguments and the number of methods per class are minimized: Easier software maintenance, less coupling between your methods, better information hiding, methods which are easier to reuse, and easier correctness proofs using structural induction. We show relationships between the Law and software engineering techniques, such as coupling control, information hiding, information restriction, localization of information, narrow interfaces and structural induction. We discuss two important interpretations of the Law (strong and weak) and we prove that any object-oriented program can be transformed to satisfy the Law. We express the Law in several languages which support object-oriented p...

Previous research has shown that the SPEC benchmarks achieve low miss ratios in relatively small instruction caches. This paper presents evidence that current software-development practices produce applications that exhibit substantially higher instruction-cache miss ratios than do the SPEC benchmarks. To represent these trends, we have assembled a collection of applications, called the Instruction Benchmark Suite (IBS), that provides a better test of instruction-cache performance. We discuss the rationale behind the design of IBS and characterize its behavior relative to the SPEC benchmark suite. Our analysis is based on trace-driven and trap-driven simulations and takes into full account both the application and operating-system components of the workloads. This paper then reexamines a collection of previously-proposed hardware mechanisms for improving instruction-fetch performance

The metrics suite for object-oriented design put forward by Chidamber and Kemerer [8] is partly evaluated by applying principles of measurement theory. Using the object coupling measure (CBO) as an example, it is shown that failing to establish a sound empirical relation system can lead to deficiencies of software metrics. Similarly, for the object-oriented cohesion measure (LCOM) it is pointed out that the issue of empirical testing the representation condition must not be ignored, even if other validation principles are carefully obeyed. As a by-product, an alternative formulation for LCOM is proposed. Index Terms Software Measurement, Coupling Metrics, Cohesion Metrics, Object-Orientation,Validation Copyright Notice This paper has been published in IEEE Transactions on Software Engineering, Vol. 22, No. 4, April 1996. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new coll...

We review propagation patterns for describing object-oriented software at a higher level of abstraction than the one used by today's programming languages. A propagation pattern defines a family of programs from which we can select a member by giving a class dictionary graph which details the structure of behavior through part-of and inheritance relationships between classes. The paper introduces three concepts: evolution histories, growth-plans and a propagation directive calculus. Evolution histories describe a sequence of development phases of an object-oriented program, each phase being executable and therefore testable. To keep the programs flexible and short, we describe them in terms of propagation patterns. Each phase of an evolution history is tested in small steps which are constrained by class dictionary graphs belonging to a growth-plan. Propagation directives are useful both for describing propagation patterns and growth-plans and therefore we endow propagation di...

It is widely agreed that recursive types are inherent in the static typing of the essential mechanisms of objectoriented programming: encapsulation, message passing, subtyping, and inheritance. We demonstrate here that modeling object encapsulation in terms of existential types yields a substantially more straightforward explanation of these features in a simpler calculus without recursive types. 1 Introduction Static type systems for object-oriented programming languages have progressed significantly in the past decade. The line of research begun by Cardelli [11] and continued by Cardelli [18, 17, 14, 13], Mitchell [32, 10, 33], Bruce [8, 5, 7], and others [31, 39, 21, 10, 23, 20, 19, 26, 29, 44, 45, 46] has culminated in type-theoretic accounts [6, 14] of many of the features of languages like Smalltalk [28]. Our goal here is to reformulate the essential mechanisms of these accounts using a simpler type theory: we give a complete model of encapsulation, message passing, subtyping, ...

Object-oriented system development is gaining wide attention both in research environments and in industry. A severe problem encountered, however, is the quickly increasing complexity of such systems and the lack of adequate criteria and guidelines for "good" designs. To cope with this problem, it is imperative to better understand the properties and characteristics of object-oriented systems. In this paper, we extend the concepts of coupling and cohesion developed initially for procedure-oriented systems to object-oriented systems. Coupling describes the interdependency between methods and between object classes, respectively. Cohesion describes the binding of the elements within one method and within one object class, respectively. We introduce a comprehensive taxonomy of coupling and cohesion properties of object-oriented systems and provide guidelines for improving these properties. CR Classification: D.1.5 [Software]: Object-Oriented Programming; D.2.3 [Soft- ware]: Coding -- sta...

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A well-known shortcoming of the object model of Simula and Smalltalk is the inability to deal cleanly with methods that require access to the internal state of more than one object at a time. Recent language designs have therefore extended the basic object model with notions such as friends' methods and protected features, which allow external access to the internal state of objects but limit the scope in which such access can be used. We show that a variant of this idea can be added to any type-theoretic model of the basic object-oriented mechanisms (encapsulation, message passing, and inheritance), using a construction based on Cardelli and Wegner's partially abstract types, a refinement of Mitchell and Plotkin's type-theoretic treatment of abstract types.

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