FILTEBSSupporting both intraclass and interclass crosscutting through model extension. conl-olfs]^fii)nization, and object interactions cannot be expressed O languages as a separate software module [4, 7]. These jgas a single module, its adaptability and reusability are likely to be reduced. A num-Lodewijk Bergmans and MehmetAksit ber of progratnming techniques have been proposed to express crosscutting concerns, for example, adaptive programming [9], AspectJ [8], Hyperspaces [10], and Composition Filters [1]. Here, we present the Composition Filters (CF) model and illustrate how it addresses evolving crosscutting concerns. The filters in the CF model can express crosscutting concerns by modular and orthogonal enhancements to o^cts. Here, modularity

It is generally claimed that object-based models are very suitable for building distributed system architectures since object interactions follow the clientserver model. To cope with the complexity of today's distributed systems, however, we think that high-level linguistic mechanisms are needed to effectively structure, abstract and reuse object interactions. For example, the conventional object-oriented model does not provide high-level language mechanisms to model layered system architectures. Moreover, we consider the message passing model of the conventional object-oriented model as being too low-level because it can only specify object interactions that involve two partner objects at a time and its semantics cannot be extended easily. This paper introduces Abstract Communication Types (ACTs), which are objects that abstract interactions among objects. ACTs make it easier to model layered communication architectures, to enforce the invariant behavior among objects, to reduce the complexity of programs by hiding the interaction details in separate modules and to improve reusability through the application of objectoriented principles to ACT classes. We illustrate the concept of ACTs using the composition filters model.

No abstract

This paper introduces a new model, based on so-called object-composition filters, that uniformly integrates database-like features into an object-oriented language. The focus is on providing persistent dynamic data structures, data sharing, transactions, multiple views and associative access, integrated with the object-oriented paradigm. The main contribution is that the database-like features are part of this new object-oriented model, and therefore, are uniformly integrated with object-oriented features such as data abstraction, encapsulation, message passing and inheritance. This approach eliminates the problems associated with existing systems such as lack of reusability and extensibility for database operations, the violation of encapsulation, the need to define specific types such as sets, and the incapability to support multiple views. The model is illustrated through the object-oriented language Sina.

No abstract

No abstract

The increasing size and complexity of software systems has led to an amplified number of potential failures and as such makes it harder to ensure software reliability. Since it is usually hard to prevent all the failures, fault tolerance techniques have become more important. An essential element of fault tolerance is the recovery from failures. Local recovery is an effective approach whereby only the erroneous parts of the system are recovered while the other parts remain available. For achieving local recovery, the architecture needs to be decomposed into separate units that can be recovered in isolation. Usually, there are many different alternative ways to decompose the system into recoverable units. It appears that each of these decomposition alternatives performs differently with respect to availability and performance metrics. We propose a systematic approach dedicated to optimizing the decomposition of software architecture for local recovery. The approach provides systematic guidelines to depict the design space of the possible decomposition alternatives, to reduce the design space with respect to domain and stakeholder constraints and to balance the feasible alternatives with respect to availability and performance. The approach is supported by an integrated set of tools and illustrated for the open-source MPlayer software.

Real-time programs are, in general, difficult to design and verify. The inheritance mechanism can be useful in reusing well-defined and verified real-time programs. In applications developed by current real-time objectoriented languages, however, changing application requirements or changing real-time specifications in subclasses may require excessive redefinitions although this seems to be intuitively unnecessary. We refer to this as the real-time specification inheritance anomaly. This paper introduces three kinds of real-time specification inheritance anomalies that one may experience while constructing object-oriented programs. As a solution to these anomalies, the concept of real-time composition filters is introduced. Filters affect the real-time characteristics of messages that are received or sent by an object. Through proper configuration of filters, one can specify real-time constraints, and reuse of these constraints without causing inheritance anomalies.