Stein Krogdahl

From Object-Orientation to Formal Methods

The development of the programming languages Simula I and Simula 67 is briefly described. An attempt is made also to explain the cultural impact of the languages, in particular the object oriented

Multiple inheritance in simula-like languages

This paper examines the subclass mechanism offered in the Simula language, and discusses how the flexibility of this mechanism would be enhanced if more than one prefix were allowed for classes (multiple inheritance). A strategy is presented for implementing this with efficiency comparable to that of current Simula.

Exploring the use of Package Templates for flexible re-use of Collections of related Classes

It has been recognized that there is a need for a language mechanism that support reuse of collections of related classes. Existing approaches either use an enclosing class for this purpose, or introduce a special purpose, new language construct. In this paper we explore the use of packages for the grouping of related classes. Ordinary packages are already grouping of classes, so we explore the combination of packages and templates, i.e. package templates. By instantiating package templates, the classes of the package templates are provided as if ordinary packages are produced and imported.

A Collection Operator for Graph Transformation

Graph transformation has a well-established theory and associated tools that can be used to perform model transformations. However, the lack of a construct to match and transform collections of similar subgraphs makes graph transformation complex or even impractical to use in a number of transformation cases. This is addressed in this paper, by defining a collection operator which is powerful, yet fairly simple to model and understand. We present model transformation examples from different modeling domains to illustrate the benefit of the approach.

Groovy package templates: supporting reuse and runtime adaption of class hierarchies

We show how package templates, a modularization mechanism originally developed for statically typed languages like Java and C#, can be applied to and implemented in a dynamic language like Groovy, by using the languages capabilities for meta-programming. We then consider a set of examples and discuss dynamic PT from the viewpoints of code modularization and reuse, and dynamic adaption of classes at runtime.

Semantics-Based Weaving of UML Sequence Diagrams

In this paper we briefly introduce an aspect language that can define cross-cutting effects on a set of UML 2.0 sequence diagrams. Our main contribution is to weave aspects and sequence diagrams at the model level. By basing the weaving upon a formal trace model for sequence diagrams, we ensure that the weaving is semantics-based. To avoid the intractability of working on complete trace sets, we define a lifeline-based weaving upon trace-based equivalence classes. A major challenge is to handle unbounded loops which produce infinite trace sets. We establish a systematic way to rewrite the original loop definition so that the weaving can be performed on a finite structure. A weaving tool has been implemented to validate the approach.

A Top Down Approach to the Formal Specification of SCI Cache Coherence

The paper gives an introduction to an ongoing effort of formally specifying and verifying the cache coherence protocol of the new IEEE interconnect standard called the Scalable Coherent Interface. We first give the the most abstract (top level) specification of a memory system. We then introduce a private cache for each processor, and specify the notion of cache coherence. We refine the specifications of the memory operations for use with caches, and finally outline the more complex bottom layers where directory structures and concurrency are introduced.

The Birth of Simula

When designing Simula, Ole-Johan Dahl and Kristen Nygaard introduced the basic concepts of what later became object-orientation, which still, 35 years later, has a profound impact on computing. This paper looks at the background for the Simula project, the way it developed over time, and the reason it could became so successful.

A Semantics-Based Aspect Language for Interactions with the Arbitrary Events Symbol

In this paper we introduce an aspect language that can define cross-cutting effects on a set of UML 2.0 sequence diagrams. The aspects and sequence diagrams are woven at the model level. By basing the weaving upon a formal trace model for sequence diagrams, we ensure that the weaving is semantics-based. We propose the arbitrary events symbolas a wildcard mechanism to express zero or more events on a sequence diagram lifeline. The approach is explained by a real-life example, and a weaving tool partially implements the approach.

A linked list cache coherence protocol: verifying the bottom layer

High performance and correctness are crucially important in hardware development. This paper discusses aspects of correctness of a linked list cache coherence protocol. The protocol is tailored to execute as many operations as possible in parallel, achieving speed and avoiding the memory bottleneck. This makes it hard to verify that the protocol is correct. In the paper, a bottom layer of the protocol is identified and it is shown how the correctness of this layer can be established.<<ETX>>