Abstract. This paper presents ABS, an abstract behavioral specification language for designing executable models of distributed object-oriented systems. The language combines advanced concurrency and synchronization mechanisms for concurrent object groups with a functional language for modeling data. ABS uses asynchronous method calls, interfaces for encapsulation, and cooperative scheduling of method activations inside concurrent objects. This feature combination results in a concurrent object-oriented model which is inherently compositional. We discuss central design issues for ABS and formalize the type system and semantics of Core ABS, a calculus with the main features of ABS. For Core ABS, we prove a subject reduction property which shows that well-typedness is preserved during execution; in particular, "method not understood" errors do not occur at runtime for well-typed ABS models. Finally, we briefly discuss the tool support developed for ABS.

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Abstract. We present the semantics and proof system for an objectoriented language with active objects, asynchronous method calls, and futures. The language, based on Creol, distinguishes itself in that unlike active object models, it permits more than one thread of control within an object, though, unlike Java, only one thread can be active within an object at a given time and rescheduling occurs only at specific release points. Consequently, reestablishing an object's monitor invariant is possible at specific well-defined points in the code. The resulting proof system shows that this approach to concurrency is simpler for reasoning than, say, Java's multithreaded concurrency model. From a methodological perspective, we identify constructs which admit a simple proof system and those which require, for example, interference freedom tests.

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.

International audienceA recent trend in programming language research is to use behavioral type theory to ensure various correctness properties of largescale, communication-intensive systems. Behavioral types encompass concepts such as interfaces, communication protocols, contracts, and choreography. The successful application of behavioral types requires a solid understanding of several practical aspects, from their representation in a concrete programming language, to their integration with other programming constructs such as methods and functions, to design and monitoring methodologies that take behaviors into account. This survey provides an overview of the state of the art of these aspects, which we summarize as the pragmatics of behavioral types