Ahmed Mostefaoui

Semantic Based Prefetching in News-on-Demand Video Servers

In video databases, a video document has two abstractions. The high level abstraction corresponds to the view in which the contents of that video document are seen by end users, and the low level abstraction corresponds to the physical organization of that video document. Due to the huge size of continuous data, reducing I/O has become a key issue. The latter has been mostly addressed by developing appropriate buffering techniques. In addition, prefetching techniques play a major role to meet the video data requirements. In this paper, we propose a novel prefetching strategy based not only on run-time information (objects access frequencies for example) but also on knowledge about clips structures. The proposed technique merges the two views of a video document to trigger prefetching at the video server level. Simulation experiments for a News-on-Demand application performed on different request scenarios show an improvement of about 18% in the buffer hit-rate with respect, first to the available buffer size and second to the request arrival rate.

Multi-clip query optimization in video databases

A multi-clip query requests multiple video clips. We address the multi-clip query optimization problem. We propose a new heuristic called restricted search interval that maximizes clip sharing between queries and consequently reduces the workload of the video server. The experimental results show that the suggested heuristics reduce the server workload by about 68.7% in comparison to a classical heuristic approach.

Localization and Coverage for High Density Sensor Networks

The only power source of nodes in sensor networks is usually provided by batteries which have a determined lifetime. In order to increase the total network lifetime, neighbors nodes can alternate between active (receive, transmit...) and sleep mode. The objective is to find sets of active nodes that ensure as much as possible the zone coverage. In this paper, we will introduce a new method for nodes scheduling in sensor networks. We exploit a mobile beacon localization approach to construct sets of active nodes. The mobile beacon follows the Hilbert space filling curve, that has several properties. It divides the area into unit squares by the mean of linear ordering. In our approach, we chose the Hilbert curve order, in a way that, every unit square will be covered by one and only one sensor node and all the reminder nodes inside this unit square will go to sleep until the first node dies. It is an energy saved approach because nodes communicate only with the mobile beacon. The experimental studies we conducted, confirmed the effectiveness of our approach

Heuristics for Optimizing Multi-Clip Queries in Video Databases

In this paper we address the multi-clip query optimization problem where a multi-clip query requests multiple video clips. We propose a new heuristics called Restricted Search Interval that maximizes clip sharing between queries and consequently reduces the network bandwidth of a video server for a multicast system. An adaptation of our heuristics for optimizing the response time of the query is also presented. The experimental results show that the suggested heuristics reduces the server workload by about 28% on the average in comparison to a classical heuristic approach.

SIRSALE: a large scale video indexing and content-based retrieving system

This paper presents the SIRSALE system. SIRSALE is a video management system that allows users to deal with video streams stored in distributed repositories. SIRSALE is based on a modular model that allows adapting the system to deal with specific semantic contexts. Thus SIRSALE allows users to browse documents by structures (shots, scenes, sequences), to annotate the content of the video documents and to query the database by content, by using a graphical tool adapted to the users specific topic of interest. The system has been demonstrated to professionals with a positive feedback.

SIRSALE: integrated video database management tools

Video databases became an active field of research during the last decade. The main objective in such systems is to provide users with capabilities to friendly search, access and playback distributed stored video data in the same way as they do for traditional distributed databases. Hence, such systems need to deal with hard issues : (a) video documents generate huge volumes of data and are time sensitive (streams must be delivered at a specific bitrate), (b) contents of video data are very hard to be automatically extracted and need to be humanly annotated. To cope with these issues, many approaches have been proposed in the literature including data models, query languages, video indexing etc. In this paper, we present SIRSALE : a set of video databases management tools that allow users to manipulate video documents and streams stored in large distributed repositories. All the proposed tools are based on generic models that can be customized for specific applications using ad-hoc adaptation modules. More precisely, SIRSALE allows users to : (a) browse video documents by structures (sequences, scenes, shots) and (b) query the video database content by using a graphical tool, adapted to the nature of the target video documents. This paper also presents an annotating interface which allows archivists to describe the content of video documents. All these tools are coupled to a video player integrating remote VCR functionalities and are based on active network technology. So, we present how dedicated active services allow an optimized video transport for video streams (with Tamanoir active nodes). We then describe experiments of using SIRSALE on an archive of news video and soccer matches. The system has been demonstrated to professionals with a positive feedback. Finally, we discuss open issues and present some perspectives.

Distributed Video Documents Indexing and Content-Based Retrieving

In this paper, we present SIRSALE: a set of distributed video documents management tools that allow users to manipulate video streams stored in large distributed repositories. All the proposed tools are based on generic models that can be customized for specific applications using ad-hoc adaptation modules. More precisely, SIRSALE allows users to: (a) browse video documents by structures (sequences, scenes, shots) and (b) query the video database content by using a graphical tool, adapted to the nature of the target video documents. This paper also presents an annotating interface which allows archivists to describe the content of video documents. All these tools are coupled to a video player integrating remote VCR functionalities and are based on active network technology. We then describe experiments of using SIRSALE on an archive of news video and soccer matches. The system has been demonstrated to professionals with a positive feedback. Finally, we discuss open issues and present some perspectives.

Une approche robuste pour la prolongation de la durée de vie des réseaux ad hoc multimédias

In wireless ad hoc networks, nodes are energy constrained. As they communicate far off destinations using intermediate relays, it may not be in interest of a node to expend its energy in relaying and consequently reducing its own lifetime. On the other hand, if all nodes decide not to always accept relay requests, the network throughput will drop dramatically i.e., the lifetime of the whole network is reduced. Obviously, from a single node point of view, these two extreme attitudes are opposite to its interest. We addressed this issue by proposing a novel distributed approach that guarantees tasks affectation to nodes with regard to their energy constraints. The key idea behind is to guarantee to all nodes that they share tasks in function of their energy provisions. In this paper, we tackle the problem of nodes mobility and its impact on the behavior of our proposed approach. We evaluated the performance of our approach under several scenrios and showed that it still improves the network lifetime.