Probabilistic latency for partial ordering

International audienceOrdering events in a distributed systems consists fundamentally in delaying event delivery. Partial ordering, such as FIFO and causal order, has many practical usages in distributed systems and can be obtained in arbitrarily large and dynamic networks. However, partial orderings imply that messages cannot be sent and delivered as soon as produced. In this paper, we examine the latency induced by such partial orderings. We obtain a probabilistic measure of the moment a message can be delivered according the different characteristics of the distributed system. Having such a measure helps to understand the systems behavior and to design new protocols. For instance, our measure allows us to parametrize a naive, albeit efficient, fault-tolerant causal delivery mechanism. We experimentally validate our approach using Internet-scale production distribution latency including faults

Change-centric improvement of team collaboration

In software development, teamwork is essential to the successful delivery of a final product. The software industry has historically built software utilizing development teams that share the workplace. Process models, tools, and methodologies have been enhanced to support the development of software in a collocated setting. However, since the dawn of the 21st century, this scenario has begun to change: an increasing number of software companies are adopting global software development to cut costs and speed up the development process. Global software development introduces several challenges for the creation of quality software, from the adaptation of current methods, tools, techniques, etc., to new challenges imposed by the distributed setting, including physical and cultural distance between teams, communication problems, and coordination breakdowns. A particular challenge for distributed teams is the maintenance of a level of collaboration naturally present in collocated teams. Collaboration in this situation naturally d r ops due to low awareness of the activity of the team. Awareness is intrinsic to a collocated team, being obtained through human interaction such as informal conversation or meetings. For a distributed team, however, geographical distance and a subsequent lack of human interaction negatively impact this awareness. This dissertation focuses on the improvement of collaboration, especially within geographically dispersed teams. Our thesis is that by modeling the evolution of a software system in terms of fine-grained changes, we can produce a detailed history that may be leveraged to help developers collaborate. To validate this claim, we first c r eate a model to accurately represent the evolution of a system as sequences of fine- grained changes. We proceed to build a tool infrastructure able to capture and store fine-grained changes for both immediate and later use. Upon this foundation, we devise and evaluate a number of applications for our work with two distinct goals: 1. To assist developers with real-time information about the activity of the team. These applications aim to improve developers’ awareness of team member activity that can impact their work. We propose visualizations to notify developers of ongoing change activity, as well as a new technique for detecting and informing developers about potential emerging conflicts. 2. To help developers satisfy their needs for information related to the evolution of the software system. These applications aim to exploit the detailed change history generated by our approach in order to help developers find answers to questions arising during their work. To this end, we present two new measurements of code expertise, and a novel approach to replaying past changes according to user-defined criteria. We evaluate the approach and applications by adopting appropriate empirical methods for each case. A total of two case studies – one controlled experiment, and one qualitative user study – are reported. The results provide evidence that applications leveraging a fine-grained change history of a software system can effectively help developers collaborate in a distributed setting

Consistance et protection des données dans les systèmes collaboratifs par les méthodes formelles

Le développement de logiciels complexes ou de contenus multimédias implique de nos jours plusieurs personnes de plus en plus géographiquement dispersées à travers le monde qui collaborent à travers des systèmes d’édition collaborative. Le but principal de cette collaboration est l’amélioration de la productivité et la réduction du temps et des coûts de développement. L’un des défis majeurs de ces outils d’édition collaborative est d’assurer la convergence et la fiabilité des données partagées. Pour répondre à ce défi, plusieurs approches existent dans la littérature parmi lesquelles, nous avons l’approche multiversions (MV), l’approche des types de données commutatives répliquées (CRDT) et l’approche de la transformée opérationnelle (OT). La première se base sur le principe du copier, modifier et fusionner et utilise un serveur central chargé de la fusion des différentes copies provenant des sites participant à la collaboration. Les modifications effectuées par chaque site sur sa copie ne sont fusionnées à la copie centrale qu’à la demande de l’utilisateur. La difficulté majeure de cette approche est le coût lié au stockage des diverses versions sur le serveur, l’utilisation d’estampilles pour ordonner les opérations lors de la fusion. Ce qui la rend difficilement utilisable dans un contexte d’environnement distribué. La deuxième approche considère que toutes les opérations sont commutatives donc pouvant être exécutées dans un ordre quelconque. Quant à la dernière approche, elle s’appuie sur une transformation des opérations reçues des sites distants par rapport à celles qui leur sont concurrentes. Dans cette approche, un algorithme de transformation inclusive (IT) est utilisé afin d’assurer la convergence des copies, mais la plupart des algorithmes proposés dans la littérature ne satisfont pas les critères de convergence. En plus de la cohérence, la fiabilité des données reste un autre défi dans les systèmes collaboratifs. Pour faire face à ce défi, plusieurs applications encapsulent, dans leur code source, des fonctionnalités transverses telles que celles de sécurité afin de répondre aux exigences de confidentialité et d’intégrité des données. Dans la littérature, la programmation orientée aspect (AOP) est l’une des approches utilisées afin d’assurer la modularité, la maintenabilité et la réutilisation des composants d’un logiciel. Une des difficultés de ce paradigme de programmation est l’assurance qu’une propriété de sécurité reste satisfaite après le tissage entre le programme de base et tous les aspects encapsulant les préoccupations transverses. Ce qui implique de trouver des techniques automatiques de vérification des propriétés de sécurité une fois le tissage fait. Dans le registre de la fiabilité des données, le contrôle d’accès joue un rôle prépondérant. Ainsi, en ce qui concerne le partage de contenus multimédias publiés sur le Web, il est nécessaire de collaborer pour les alimenter, mais un des défis majeurs est de les rendre fiables.----------ABSTRACT: Complex software and Web content development involve nowadays multiple programmers located in different areas working together on the same development project using collaborative systems in order to achieve efficiency, improve productivity and reduce development time. One of the key challenge in such a development environment is ensuring the convergence and the reliability of the shared data or content. In the literature, many approaches have been proposed to face this challenge. Among those approaches, we have multi-version (MV), commutative replication data type (CRDT) and operational transformation (OT) approach. The first approach is based on the "copy, modify and merge" principle and uses a central server to merge the updates from the different sites participating in the collaboration. The local updates of a specific site are merged only on demand. The key drawback of this approach is the storage cost of the various versions on the server and the overhead due to the generation of stamps for the operations ordering. Thus, this drawback makes this approach difficult to use in the context of a distributed collaborative environment. The second approach preconizes that all the operations are commutative so that they can be executed in any given order. The latter approach is based on the transformation of all the operations received from the remote sites against their concurrent operations before being merged. In this approach, an inclusive transformation algorithm is used in order to ensure the convergence criteria. Unfortunately, most of the proposed algorithms in the literature do not satisfy the convergence criteria. Beside the convergence, the reliability of the data remains another challenge in the collaborative systems. In order to face this challenge, many programs encapsulate crosscutting concerns (e.g. security, logging) for data confidentiality and integrity purposes. In the literature, aspect-oriented programming (AOP) is one the approaches used to better modularize the separation of concerns in order to make easier the maintenance and the reuse of the software components. However, one challenge of this paradigm is the insurance that a given property such as security one remains satisfied after the weaving of the base program and the aspects. Thus, we may find automated way to verify such security properties in the woven program. Concerning data reliability, access control is one of the major piece of the puzzle. Thus, in the Web content publication, one challenge is to collaborate in order to produce them and the other key challenge is to make them reliable

Supporting Collaboration Awareness with Real-time Visualization of Development Activity

In the context of multi-developer projects, where several people are contributing code, developers must deal with concurrent development. Collaboration among developers assumes a fundamental role, and failing to address it can result, for example, in shipping delays. We argue that tool support for collaborative software development augments the level of awareness of developers, and consequently, help them to collaborate and coordinate their activities. In this context, we present an approach to augment awareness by recovering development information in real time and broadcasting it to developers in the form of three lightweight visualizations. Scamp, the Eclipse plug-in supporting this, is part of our Syde tool to support collaboration. We illustrate the usage of Scamp in the context of two multi-developer projects. Preprint accepted for publication in the Proceedings of the 14th European Conference on Software Maintenance and Reengineering (CSMR2010), Madrid (Spain), 15-18 March, 2010, IEEE Computer Society, 2010.Software TechnologyElectrical Engineering, Mathematics and Computer Scienc