Jörg Kienzle

AOP: Does It Make Sense? The Case of Concurrency and Failures

Concurrency and failures are fundamental problems in distributed computing. One likes to think that the mechanisms needed to address these problems can be separated from the rest of the distributed application: in modern words, these mechanisms could be aspectized. Does this however make sense?This paper relates an experience that conveys our initial and indeed biased intuition that the answer is in general no. Except for simple academic examples, it is hard and even potentially dangerous to separate concurrency control and failure management from the actual application.We point out the very facts that (1) an aspect-oriented language can, pretty much like a macro language, be beneficial for code factorization (but should be reserved to experienced programmers), and (2) concurrency and failures are particularly hard to aspectize because they are usually part of the phenomenon that objects should simulate. They are in this sense different than other concerns, like for instance tracing, which might be easier to aspectize.

Comparing interest management algorithms for massively multiplayer games

Broadcasting all state changes to every player of a massively multiplayer game is not a viable solution. To successfully overcome the challenge of scale, massively multiplayer games have to employ sophisticated interest management techniques that only send relevant state changes to each player. This paper compares the performance of different interest management algorithms based on measurements obtained in a real massively multiplayer game using human and computer-generated player actions. We show that interest management algorithms that take into account obstacles in the world reduce the number of update messages between players by up to a factor of 6, and that some computationally inexpensive tile-based interest management algorithms can approximate ideal visibility-based interest management at very low cost. The experiments also show that measurements obtained with computer-controlled players performing random actions can approximate measurements of games played by real humans, provided that the starting positions of the random players are chosen adequately. As the size of the world and the number of players of massively multiplayer games increases, adaptive interest management techniques such as the ones studied in this paper will become increasingly important.

Crisis management systems: a case study for aspect-oriented modeling

The intent of this document is to define a common case study for the aspect-oriented modeling research community. The domain of the case study is crisis management systems, i.e., systems that help in identifying, assessing, and handling a crisis situation by orchestrating the communication between all parties involved in handling the crisis, by allocating and managing resources, and by providing access to relevant crisis-related information to authorized users. This document contains informal requirements of crisis management systems (CMSs) in general, a feature model for a CMS product line, use case models for a car crash CMS (CCCMS), a domain model for the CCCMS, an informal physical architecture description of the CCCMS, as well as some design models of a possible object-oriented implementation of parts of the CCCMS backend. AOM researchers who want to demonstrate the power of their AOM approach or technique can hence apply the approach at the most appropriate level of abstraction.

AO challenge - implementing the ACID properties for transactional objects

This paper presents a challenge case study to the aspect-oriented community: ensuring the ACID properties (atomicity, consistency, isolation and durability) for transactional objects. We define a set of ten base aspects, each one providing a well-defined reusable functionality. The base aspects are simple, yet have complex dependencies among each other. We then show how these base aspects can be configured and composed in different ways to implement different concurrency control and recovery strategies. This composition is delicate: some aspects conflict with each other, others have to be reconfigured dynamically at run-time. We believe that this case study can serve as a benchmark for aspect-oriented software development, in particular for evaluating the expressivity of aspect-oriented programming languages, the performance of aspect-oriented programming environments, and the suitability of aspect-oriented modeling notations.

Concern-Oriented Software Design

There exist many solutions to solve a given design problem, and it is difficult to capture the essence of a solution and make it reusable for future designs. Furthermore, many variations of a given solution may exist, and choosing the best alternative depends on application-specific high-level goals and non-functional requirements. This paper proposes Concern-Oriented Software Design, a modelling technique that focuses on concerns as units of reuse. A concern groups related models serving the same purpose, and provides three interfaces to facilitate reuse. The variation interface presents the design alternatives and their impact on non-functional requirements. The customization interface of the selected alternative details how to adapt the generic solution to a specific context. Finally, the usage interface specifies the provided behaviour. We illustrate our approach by presenting the concern models of variations of the Observer design pattern, which internally depends on the Association concern to link observers and subjects.

Mammoth: a massively multiplayer game research framework

This paper presents Mammoth, a massively multiplayer game research framework designed for experimentation in an academic setting. Mammoth provides a modular architecture where different components, such as the network engine, the replication engine, or interest management, can easily be replaced. Subgames allow a researcher to define different game goals, for instance, in order to evaluate the effects of different team-play tactics on the game performance. Mammoth also offers a modular and flexible infrastructure for the definition of non-player characters with behavior controlled by complex artificial intelligence algorithms. This paper focuses on the Mammoth architecture, demonstrating how good design practices can be used to create a modular framework where researchers from different research domains can conduct their experiments. The effectiveness of the architecture is demonstrated by several successful research projects accomplished using the Mammoth framework.

Model-driven assessment of system dependability

Designers of complex real-time systems need to address dependability requirements early on in the development process. This paper presents a model-based approach that allows developers to analyse the dependability of use cases and to discover more reliable and safe ways of designing the interactions of the system with the environment. The hardware design and the dependability of the hardware to be used also needs to be considered. We use a probabilistic extension of statecharts to formally model the interaction requirements defined in the use cases. The model is then evaluated analytically based on the success and failure probabilities of events. The analysis may lead to further refinement of the use cases by introducing detection and recovery measures to ensure dependable system interaction. A visual modelling environment for our extended statecharts formalism supporting automatic probability analysis has been implemented in AToM3, A Tool for Multi-formalism and Meta-Modelling. Our approach is illustrated with an elevator control system case study.

The relevance of model-driven engineering thirty years from now

Although model-driven engineering (MDE) is now an established approach for developing complex software systems, it has not been universally adopted by the software industry. In order to better understand the reasons for this, as well as to identify future opportunities for MDE, we carried out a week-long design thinking experiment with 15 MDE experts. Participants were facilitated to identify the biggest problems with current MDE technologies, to identify grand challenges for society in the near future, and to identify ways that MDE could help to address these challenges. The outcome is a reflection of the current strengths of MDE, an outlook of the most pressing challenges for society at large over the next three decades, and an analysis of key future MDE research opportunities.

Open multithreaded transactions: keeping threads and exceptions under control

Although transactional models have proved to be very useful for numerous applications, the development of new models to reflect the ever-increasing complexity and diversity of modern applications is a very active area of research. Analysis of the existing models of multithreaded transactions shows that they either give too much freedom to threads and do not control their participation in transactions, or unnecessarily restrict the computational model by assuming that only one thread can enter a transaction. Another important issue, which many models do not address properly, is providing adequate exception handling features. A new model of multithreaded transactions is proposed. Its detailed description is given, including rules of thread behaviour when transactions start, commit and abort, and rules of exception raising, propagation and handling. This model is supported by enhanced error detection techniques to allow for earlier error detection and for localised recovery. General approaches to implementing transaction support are discussed and a detailed description of an Ada implementation is given. Special attention is paid to outlining typical applications for which this model is suitable and to comparing it with several known approaches (Coordinated Atomic actions, CORBA, and Argus).

TouchRAM: A Multitouch-Enabled Tool for Aspect-Oriented Software Design

This paper presents TouchRAM, a multitouch-enabled tool for agile software design modeling aimed at developing scalable and reusable software design models. The tool gives the designer access to a vast library of reusable design models encoding essential recurring design concerns. It exploits model interfaces and aspect-oriented model weaving techniques as defined by the Reusable Aspect Models (RAM) approach to enable the designer to rapidly apply reusable design concerns within the design model of the software under development. The paper highlights the user interface features of the tool specifically designed for ease of use, reuse and agility (multiple ways of input, tool-assisted reuse, multitouch), gives an overview of the library of reusable design models available to the user, and points out how the current state-of-the-art in model weaving had to be extended to support seamless model reuse.