Object-oriented distributed computing is becoming increasingly important for critical infrastructure in society. In standard objectoriented models, objects synchronize on method calls. These models may be criticized in the distributed setting for their tight coupling of communication and synchronization; network delays and instabilities may locally result in much waiting and even deadlock. The Creol model targets distributed objects by a looser coupling of method calls and synchronization. Asynchronous method calls and high-level local control structures allow local computation to adapt to network instability. Object variables are typed by interfaces, so communication with remote objects is independent from their implementation. The inheritance and subtyping relations are distinct in Creol. Interfaces form a subtype hierarchy, whereas multiple inheritance is used for code reuse at the class level. This paper presents the Creol syntax, operational semantics, and type system. It is shown that runtime type errors do not occur for well-typed programs.

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We propose a new and systematic framework for proof reuse in the context of deductive software verification. The framework generalizes abstract contracts into incremental proof repositories. Abstract contracts enable a separation of concern between called methods and their implementations, facilitating proof reuse. Proof repositories allow the systematic caching of partial proofs that can be adapted to different method implementations. The framework provides flexible support for verification-in-the-large in the context of, e.g., partly developed programs, evolution of programs and contracts, and product variability.Partly funded by the EU project H2020-644298 HyVar: Scalable Hybrid Variability for Distributed Evolving Software Systems (www.hyvar-project.eu), the EU project FP7-610582 Envisage: Engineering Virtualized Services (www.envisage-project.eu), the Ateneo/CSP project RunVar, and the ICT COST Actions IC1402 ARVI (www.cost-arvi.eu) and IC1201 BETTY (www.behavioural-types.eu).