Alisdair Wren

If you would like to contact me, my address is 'asw' at this site's address without the 'www.', or you can find me on LinkedIn and Facebook.


My professional interests lie predominantly with anything complicated that can be reasoned about or solved using mathematical and logical techniques. A bit more specifically:


I have recently finished a PhD from the University of Cambridge Computer Laboratory under Dr Gavin Bierman and Prof. Andrew Pitts. My thesis was on "Relationships for object-oriented programming languages", and demonstrates how inter-object relationships are lacking in object-oriented programming languages, and shows how to extend class-based (e.g. Java, C#) and object-based (e.g. Javascript, or the ς-calculi) languages in a type-safe way.

Relationships for object-oriented programming languages

Thesis in PDF format (1115KB)

Abstract: Object-oriented approaches to software design and implementation have gained enormous popularity over the past two decades. However, whilst models of software systems routinely allow software engineers to express relationships between objects, object-oriented programming languages lack this ability. Instead, relationships must be encoded using complex reference structures. When the model cannot be expressed directly in code, it becomes more difficult for programmers to see a correspondence between design and implementation --- the model no longer faithfully documents the code. As a result, programmer intuition is lost, and error becomes more likely, particularly during maintenance of an unfamiliar software system.

This thesis explores extensions to object-oriented languages so that relationships may be expressed with the same ease as objects. Two languages with relationships are specified: RelJ, which offers relationships in a class-based language based on Java, and Qς, which is an object calculus with heap query.

In RelJ, relationship declarations exist at the same level as class declarations: relationships are named, they may have fields and methods, they may inherit from one another and their instances may be referenced just like objects.

Moving into the object-based world, Qς is based on the ς-calculi of Abadi and Cardelli, extended with the ability to query the heap. Heap query allows objects to determine how they are referenced by other objects, such that single references are sufficient for establishing an inter-object relationship observable by all participants. Both RelJ and Qς are equipped with a formal type system and semantics to ensure type safety in the presence of these extensions.

By giving formal models of relationships in both class- and object-based settings, we can obtain general principles for relationships in programming languages and, therefore, establish a correspondence between implementation and design.