The Meta in Meta-object Architectures

Behavioral reflection is crucial to support for example functional upgrades, on-the-fly debugging, or monitoring critical applications. However the use of reflective features can lead to severe problems due to infinite metacall recursion even in simple cases. This is especially a problem when reflecting on core language features since there is a high chance that such features are used to implement the reflective behavior itself. In this paper we analyze the problem of infinite meta-object call recursion and solve it by providing a first class representation of meta-level execution: at any point in the execution of a system it can be determined if we are operating on a meta-level or base level so that we can prevent infinite recursion. We present how meta-level execution can be represented by a meta-context and how reflection becomes context-aware. Our solution makes it possible to freely apply behavioral reflection even on system classes: the meta-context brings stability to behavioral reflection. We validate the concept with a robust implementation and we present benchmarks.

Practical Object-Oriented Back-in-Time Debugging

Back-in-time debuggers are extremely useful tools for identifying the causes of bugs, as they allow us to inspect the past states of objects no longer present in the current execution stack. Unfortunately the "omniscient" approaches that try to remember all previous states are impractical because they either consume too much space or they are far too slow. Several approaches rely on heuristics to limit these penalties, but they ultimately end up throwing out too much relevant information. In this paper we propose a practical approach to back-in-time debugging that attempts to keep track of only the relevant past data. In contrast to other approaches, we keep object history information together with the regular objects in the application memory. Although seemingly counter-intuitive, this approach has the effect that past data that is not reachable from current application objects (and hence, no longer relevant) is automatically garbage collected. In this paper we describe the technical details of our approach, and we present benchmarks that demonstrate that memory consumption stays within practical bounds. Furthermore since our approach works at the virtual machine level, the performance penalty is significantly better than with other approaches.

Taking an Object-Centric View on Dynamic Information with Object Flow Analysis

A large body of research analyzes the runtime execution of a system to extract abstract behavioral views. Those approaches primarily analyze control flow by tracing method execution events or they analyze object graphs of heap snapshots. However, they do not capture how objects are passed through the system at runtime. We refer to the exchange of objects as the object flow, and we claim that object flow is necessary to analyze if we are to understand the runtime of an object-oriented application. We propose and detail Object Flow Analysis, a novel dynamic analysis technique that takes this new information into account. To evaluate its usefulness, we present a visual approach that allows a developer to study classes and components in terms of how they exchange objects at runtime. We illustrate our approach on three case studies.

Composing New Abstractions From Object Fragments

As object-oriented languages are extended with novel modularization mechanisms, better underlying models are required to implement these high-level features. This paper describes CELL, a language model that builds on delegation-based chains of object fragments. Composition of groups of cells is used: 1) to represent objects, 2) to realize various forms of method lookup, and 3) to keep track of method references. A running prototype of CELL is provided and used to realize the basic kernel of a Smalltalk system. The paper shows, using several examples, how higher-level features such as traits can be supported by the lower-level model.

Object-Oriented Reengineering Patterns

The rapid growth of object-oriented development over the past twenty years has given rise to many object-oriented systems that are large, complex and hard to maintain. Object-Oriented Reengineering Patterns addresses the problem of understanding and reengineering such object-oriented legacy systems. This book collects and distills successful techniques in planning a reengineering project, reverse-engineering, problem detection, migration strategies and software redesign. The material in this book is presented as a set of "reengineering patterns" --- recurring solutions that experts apply while reengineering and maintaining object-oriented systems. The principles and techniques described in this book have been observed and validated in a number of industrial projects, and reflect best practice in object-oriented reengineering.

Electronic Communications as a Distinct and Unique Object of Regulation

The present paper is an abridged version of the first chapter to the book EC Electronic Communications and Competition Law (London: Cameron May, 2007). It is intended to pinpoint the contours of the communications sector as an object of regulation - an exercise that is essential to any thoughts on appropriate regulatory design. The communications sector is defined through its salient features of being (i) network-bound; (ii) dynamic; (iii) converging; (iv) sensitive to regulation and society’s reactions; and as one (v) with special societal role and as (vi) part of the new economy.

The Software Prototype as Digital Boundary Object – A Revelatory Longitudinal Innovation Case

With the availability of lower cost but highly skilled software development labor from offshore regions, entrepreneurs from developed countries who do not have software development experience can utilize this workforce to develop innovative software products. In order to succeed in offshored innovation projects, the often extreme knowledge boundaries between the onsite entrepreneur and the offshore software development team have to be overcome. Prior research has proposed that boundary objects are critical for bridging such boundaries – if they are appropriately used. Our longitudinal, revelatory case study of a software innovation project is one of the first to explore the role of the software prototype as a digital boundary object. Our study empirically unpacks five use practices that transform the software prototype into a boundary object such that knowledge boundaries are bridged. Our findings provide new theoretical insights for literature on software innovation and boundary objects, and have implications for practice.

Periphere Wahrnehmung beim Verfolgen mehrerer Objekte

Einleitung Beim Multiple-Object-Tracking müssen mehrere, sich bewegende Zielobjekte visuell ver-folgt werden. Dabei scheint es vorteilhaft zu sein, den Blick zwischen den Zielobjekten zu verankern, um Bewegungsinformationen peripher wahrzunehmen (Fehd & Seiffert, 2010). Nach Prüfung dieser Annahme (Experiment 1) wurde getestet, wie gut und schnell auf Bewegungs- und Formveränderungen der Zielobjekte reagiert werden kann (Experiment 2), um die Funktionalität der peripheren Wahrnehmung zu überprüfen. Methode 14 Teilnehmer hatten die Aufgabe, zum Ende eines Einzelversuchs 4 aus 10 Vierecken wiederzuerkennen, die sich linear für 6 s in einem projizierten Quadrat bewegten. Dabei wurden 3 Geschwindigkeiten (6, 9 und 12°/s) in 9 Blöcken à 15 Versuchen präsentiert, um herauszufinden, bei welcher Geschwindigkeit der Blickpunkt die längste Zeit auf dem Centroid der 4 Zielobjekte liegt und damit die Zielobjekte lange peripher wahrgenommen werden. In Experiment 2 sollten Teilnehmer bei dieser „optimalen“ Geschwindigkeit auf das Anhalten der Vierecke oder deren Formveränderung zur Raute (Manipulation:0.5 s) mit Knopfdruck reagieren, bei ausbleibender Veränderung hingegen die 4 Zielobjekte wiedererkennen (3 Bedingungen in 10 Blöcken à 12 Versuchen). Erwartet wurde, dass Bewegungsveränderungen häufiger und schneller erkannt werden als Formverände-rungen. Ergebnisse Der Geschwindigkeitsvergleich in Experiment 1 ergab, dass der Blick bei 6°/s die längste Zeit (46 %) auf den Centroid gerichtet ist, F(2,132) = 9.68, p < .01, ηp2 = .13 und die 4 Ziel-objekte bei dieser Geschwindigkeit signifikant häufiger wiedererkannt werden (59 %), F(2,132) = 37.62, p < .01, ηp2 = .36. In Experiment 2 wurde festgestellt, dass Bewegungs-veränderungen häufiger erkannt werden (83 %) als Formveränderungen (59 %), F(1,78) = 65.52, p < .01, ηp2 = .46, wobei die Erkennungsleistung der 4 Zielobjekte mit Experiment 1 vergleichbar ist (58%). Diskussion Die periphere Wahrnehmung scheint immer dann funktional zu sein, wenn mehrere, für eine Aufgabe relevante Objekte gleichzeitig verfolgt werden müssen und wenn Verände-rungen, besonders der Bewegung, schnell erkannt werden müssen. Weitere Untersu-chungen sollen zeigen, ob diese Funktionalität der peripheren Wahrnehmung auch im Sport (z.B. beim gleichzeitigen Verfolgen mehrerer Gegenspieler) erkannt werden kann. Literatur Fehd, H. M. & Seiffert, A. E. (2010). Looking at the center of the targets helps multiple object tracking. Journal of Vision, 10, 1–13.