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Virtual classes allow nested classes to be refined in subclasses. In this way nested classes can be seen as dependent abstractions of the objects of the enclosing classes. Expressing dependency via nesting, however, has two limitations: Abstractions that depend on more than one object cannot be modeled and a class must know all classes that depend on its objects. This paper presents dependent classes , a generalization of virtual classes that expresses similar semantics by parameterization rather than by nesting. This increases expressivity of class variations as well as the flexibility of their modularization. Besides, dependent classes complement multimethods in scenarios where multi-dispatched abstractions rather than multi-dispatched methods are needed. They can also be used to express more precise signatures of multimethods and even extend their dispatch semantics. We present a formal semantics of dependent classes and a machine-checked type soundness proof in Isabelle/HOL [29], the first of this kind for a language with virtual classes and path-dependent types.

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This paper introduces a new model of event handling combining explicitly triggered events with events intercepted with aspect-oriented features. The model supports event abstraction, polymorphic references to events, and declarative definition of events as expressions involving references to events from other objects. We show that this model makes it easy to define a declarative and compositional notion of event-based context. We illustrate these ideas with examples in ECaesarJ, a language with concrete support for our model, and relate the events of ECaesarJ to other eventhandling and context-handling models.

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The telco industry is gradually shifting from using monolithic software packages deployed on custom hardware to using modular virtualized software functions deployed on cloudified data centers using commodity hardware. This transformation is referred to as Network Function Virtualization (NFV). The scalability of the databases (DBs) underlying the virtual network functions is the cornerstone for reaping the benefits from the NFV transformation. This paper presents an industrial experience of applying sharednothing techniques in order to achieve the scalability of a DB in an NFV setup. The special combination of requirements in NFV DBs are not easily met with conventional execution models. Therefore, we designed a special shared-nothing architecture that is based on cooperative multi-tasking using user-level threads (fibers). We further show that the fiber-based approach outperforms the approach built using conventional multi-threading and meets the variable deployment needs of the NFV transformation. Furthermore, fibers yield a simpler-to-maintain software and enable controlling a trade-off between long-duration computations and real-time requests.

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