A proof system for invariants in layered OO designs

Although invariants have a long history, their meaning in OO designs is still under discussion. OO designs often include functionality that is used by different otherwise unrelated objects (shared functionality). We identify a problem with current interpretations of invariants in such designs. OO designs are often layered, where a layer uses functionality of a lower layer (in particular, shared functionality) but has little or no involvement with higher layers. As a result, higher layers can rely on lower layer invariants and lower layers do not rely on higher layer invariants. This is not reflected by current interpretations of invariants. We propose to make layers explicit in specifications and introduce a new interpretation of invariants that exploits these layers. Furthermore, we present a sound, modular verification technique that ensures the new interpretation is satisfied

Plug-ins for ISpec

ISpec is an interface specification approach where templates provide slots to write interface requirements. These requirements can be written in various "plugin" formalisms. The practical question how to implement this in a tool is answered for regular expressions as a plug-in language. The requirements expressed by the regular expressions are used to assess the correctness of requirements expressed in sequence diagrams. In fact, an editor is coupled to the tool in which a plug-in language can be defined and a slot in a template can be linked to a particular language. The theoretical question how to formalise plug-ins in a relation calculus framework is investigated

Model and classification of database replication techniques

Construction of a universal mathematic-logical model of replication processes in data bases is considered. The fundamental definitions of notions for different types of replication are given. The classification of replication techniques is proposed and the respective efficiency criteria are determined. The variants of realization for system architecture, locking strategy, servers interaction, transaction termination, database platforms, correctness criteria of transaction terminator are discussed.Розглянуто побудову універсальної математико-логічної моделі процесів реплікації у базах даних. Наведено фундаментальні визначення понять для різних видів реплікації. Запропоновано класифікацію схем реплікації та визначено відповідні критерії ефективності. Обговорено варіанти реалізації системної архітектури, стратегії блокіровок, взаємодії серверів, завершення транзакцій, платформ баз даних, критерії коректності завершення транзакцій.Рассмотрено построение универсальной математико-логической модели процессов репликации в базах данных. Приведены фундаментальные определения понятий для разных видов репликации. Предложена классификация схем репликации и определены соответствующие критерии эффективности. Обсуждены варианты реализации системной архитектуры, стратегии блокировок, взаимодействия серверов, завершения транзакций, платформ баз данных, критерии корректности завершения транзакций

Two-photon and radiative production of muon pairs

No abstract available

A Precise Clock Synchronization Protocol

A distributed clock synchronization protocol is presented which achieves a very high precision without the need for very frequent resynchronizations. The protocol tolerates failures of the clocks: clocks may be too slow or too fast, exhibit omission failures and report inconsistent values. Synchronization takes place in synchronization rounds as in many other synchronization protocols. At the end of each round, clock times are exchanged between the clocks. Each clock applies a convergence function (CF) to the values obtained. This function estimates the difference between its clock and an average clock and corrects its clock accordingly. Clocks are corrected for drift relative to this average clock during the next synchronization round. The protocol is based on the assumption that clock reading errors are small with respect to the required precision of synchronization. It is shown that the CF resynchronizes the clocks with high precision even when relatively large clock drifts are poss..