Nobuko Yoshida

On reduction-based process semantics

A formulation of semantic theories for processes which is based on reduction relation and equational reasoning is studied. The new construction can induce meaningful theories for processes, both in strong and weak settings. The resulting theories in many cases coincide with, and sometimes generalise, observation-based formulation of behavioural equivalence. The basic construction of reduction-based theories is studied, taking a simple name passing calculus called v-calculus as an example. Results on other calculi are also briefly discussed.

Structured Communication-Centered Programming for Web Services

This article relates two different paradigms of descriptions of communication behavior, one focusing on global message flows and another on end-point behaviors, using formal calculi based on session types. The global calculus, which originates from a Web service description language (W3C WS-CDL), describes an interaction scenario from a vantage viewpoint; the end-point calculus, an applied typed π-calculus, precisely identifies a local behavior of each participant. We explore a theory of end-point projection, by which we can map a global description to its end-point counterparts preserving types and dynamics. Three principles of well-structured description and the type structures play a fundamental role in the theory.

Structured communication-centred programming for web services

This paper relates two different paradigms of descriptions of communication behaviour, one focussing on global message flows and another on end-point behaviours, using formal calculi based on session types. The global calculus, which originates from a web service description language (W3C WS-CDL), describes an interaction scenario from a vantage viewpoint; the end-point calculus, an applied typed π-calculus, precisely identifies a local behaviour of each participant. We explore a theory of end-point projection, by which we can map a global description to its end-point counterpart preserving types and dynamics. Three principles of well-structured description and the type structures play a fundamental role in the theory.

Graph Types for Monadic Mobile Processes

While types for name passing calculi have been studied extensively in the context of sorting of polyadic π-calculus [5, 34, 9, 28, 32, 19, 33, 10, 17], the same type abstraction is not possible in the monadic setting, which was left as an open issue by Milner [21]. We solve this problem with an extension of sorting which captures dynamic aspects of process behaviour in a simple way. Equationally this results in the full abstraction of the standard encoding of polyadic π-calculus into the monadic one: the sorted polyadic π-terms are equated by a basic behavioural equality in the polyadic calculus if and only if their encodings are equated in a basic behavioural equality in the typed monadic calculus. This is the first result of this kind we know of in the context of the encoding of polyadic name passing, which is a typical example of translation of high-level communication structures into π-calculus. The construction is general enough to be extendable to encodings of calculi with more complex operational structures.

Global Progress in Dynamically Interleaved Multiparty Sessions

A multiparty session forms a unit of structured interactions among many participants which follow a prescribed scenario specified as a global type signature. This paper develops, besides a more traditional communicationtype system, a novel static interactiontype system for global progress in dynamically interleaved multiparty sessions.

Secure Information Flow as Typed Process Behaviour

We propose a new type discipline for the π-calculus in which secure information flow is guaranteed by static type checking. Secrecy levels are assigned to channels and are controlled by subtyping. A behavioural notion of types capturing causality of actions plays an essential role for ensuring safe information flow in diverse interactive behaviours, making the calculus powerful enough to embed known calculi for type-based security. The paper introduces the core part of the calculus, presents its basic syntactic properties, and illustrates its use as a tool for programming language analysis by a sound embedding of a secure multi-threaded imperative calculus of Volpano and Smith. The embedding leads to a practically meaningful extension of their original type discipline.

Strong normalisation in the π-calculus

We introduce a typed π-calculus where strong normalisation is ensured by typability. Strong normalisation is a useful property in many computational contexts, including distributed systems. In spite of its simplicity, our type discipline captures a wide class of converging name-passing interactive behaviour. The proof of strong normalisability combines methods from typed λ-calculi and linear logic with process-theoretic reasoning. It is adaptable to systems involving state, non-determinism, polymorphism, control and other extensions. Strong normalisation is shown to have significant consequences, including finite axiomatisation of weak bisimilarity, a fully abstract embedding of the simply typed λ-calculus with products and sums and basic liveness in interaction. Strong normalisability has been extensively studied as a fundamental property in functional calculi, term rewriting and logical systems. This work is one of the first steps to extend theories and proof methods for strong normalisability to the context of name-passing processes.

Session-Based Distributed Programming in Java

This paper demonstrates the impact of integrating session types and object-oriented programming, through their implementation in Java. Session types provide high-level abstraction for structuring a series of interactions in a concise syntax, and ensure type-safe communications between distributed peers. We present the first full implementation of a language and runtime for session-based distributed programming featuring asynchronous message passing, delegation, and session subtyping and interleaving, combined with class downloading and failure handling. The compilation-runtime framework of our language effectively maps session abstraction onto underlying transports and guarantees communication safety through static and dynamic session type checking. We have implemented two alternative mechanisms for performing distributed session delegation and prove their correctness. Benchmark results show session abstraction can be realised with low runtime overhead.

A uniform type structure for secure information flow

The π-calculus is a formalism of computing in which we can compositionally represent dynamics of major programming constructs by decomposing them into a single communication primitive, the name passing. This work reports our experience in using a linear/affine typed π-calculus for the analysis and development of type systems of programming languages, focussing on secure information flow analysis. After presenting a basic typed calculus for secrecy, we demonstrate its usage by a sound embedding of the dependency core calculus (DCC) and by the development of a novel type discipline for imperative programs which extends both a secure multi-threaded imperative language by Smith and Volpano and (a call-by-value version of) DCC. In each case, the embedding gives a simple proof of noninterference.

A theory of design-by-contract for distributed multiparty interactions

Design by Contract (DbC) promotes reliable software development through elaboration of type signatures for sequential programs with logical predicates. This paper presents an assertion method, based on the π-calculus with full recursion, which generalises the notion of DbC to multiparty distributed interactions to enable effective specification and verification of distributed multiparty protocols. Centring on global assertions and their projections onto endpoint assertions, our method allows clear specifications for typed sessions, constraining the content of the exchanged messages, the choice of sub-conversations to follow, and invariants on recursions. The paper presents key theoretical foundations of this framework, including a sound and relatively complete compositional proof system for verifying processes against assertions.