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Details of Grant 

EPSRC Reference: EP/K034413/1
Title: From Data Types to Session Types---A Basis for Concurrency and Distribution
Principal Investigator: Wadler, Professor P
Other Investigators:
Yoshida, Professor N Dardha, Dr O Gay, Professor SJ
Researcher Co-Investigators:
Project Partners:
Amazon Cognizant Technology Solutions Red Hats Labs
University of California, San Diego VMware
Department: Sch of Informatics
Organisation: University of Edinburgh
Scheme: Programme Grants
Starts: 20 May 2013 Ends: 19 November 2020 Value (£): 3,956,088
EPSRC Research Topic Classifications:
Computer Sys. & Architecture Fundamentals of Computing
Software Engineering
EPSRC Industrial Sector Classifications:
Information Technologies
Related Grants:
Panel History:
Panel DatePanel NameOutcome
13 Feb 2013 Programme Grant Interviews - 13 & 14 February 2013 (ICT) Announced
Summary on Grant Application Form
We aim to solve computing's most pressing problem - concurrency and distribution - by adapting one of computing's most successful concepts - the data type. Data types codify the structure of data; session types codify the structure of communication. Session types will enable a revolution in the development of concurrent and distributed software, making it cheaper to construct and maintain, and more reliable.

Concurrency and distribution are computing's most pressing problem: unless we discover a way to routinely and reliably build concurrent and distributed systems, a half century of unprecedented technical progress will draw to a close. We are approaching the 50th anniversary of Moore's Law, the observation that component counts and clock speeds double every 18 months. No exponential improvement can continue forever, and recently this rule has changed: clock speeds now remain fixed while the number of processors doubles, so exploitation of concurrency is essential. Meanwhile, everyone now has a computer in their pocket, and these computers depend crucially on communication to achieve their function. We inhabit a world of web applications, cloud services, and mobile apps: society increasingly depends on a technological infrastructure of concurrent and distributed systems.

Programming concurrent and distributed systems is notoriously difficult. Many solutions are based on shared memory, which requires the programmer to reason about every possible interleaving by which many processors access a common resource. Shared memory scales only to a certain point; it is not appropriate for programming the server farms that drive the web or for mobile applications. The most successful solutions so far appear to be those that replace shared memory with communication as the central structuring technique. Communication usually centres around the notion of a protocol, a series of operations in a specific order. However, direct support for protocols at the language level has been lacking, as compared with data types.

The data type is one of computing's most successful concepts. Data types appear from the oldest programming language to the newest, and cover concepts ranging from a single byte to organised tables containing information on customers and orders. Types act as the fundamental unit of compositionality: the first thing a programmer writes or reads about each method is its data type, and type discipline guarantees that each call of a method matches its definition. Data types play a central role in all aspects of software, from architectural design to interactive development environments to efficient compilation.

The analogue of the data type for concurrency and distribution is the session type. A session type codifies the notion of a protocol. Session types build on data types, as data types specify the lowest level of data exchange, upon which more complex protocols are built. Just as type discipline matches use and definition of a method, so session types ensure consistency between the two ends of a communication.

We expect session types to play a role in all aspects of software. Today, architects discuss the high-level structure of a system in terms of its types, but must resort to informal notions of protocol to describe communication; in future, they will describe communication in terms of session types. Today, programmers use tools that let them search for methods and modules based on their type, and give immediate feedback if their program violates type discipline, but must resort to informal notions of protocol when coding communications; in future, they will search for components based on their session type, and get immediate feedback if their program violates session type discipline. Today, software tools exploit types to optimise code, but cannot exploit the informal notions of protocol to optimise communication; in future, communication middleware will exploit session types to support efficient messaging.
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