Charbel Joseph Rahhal

Associate professor
Computer Science - Statistics department - Section IV - Zahle
Speciality: Computer Science
Specific Speciality: Informatique

Teaching 6 Taught Courses
2006 - 2009: PhD

Henri Poincaré University (Nancy1)
Computer Science

2004 - 2005: Master of Science (MSc)

Lebanese University
Computer Science

cum laude

2003 - 2004: Master Science (Master1)

Lebanese University
Computer Science

1999 - 2003: Bachelor

Lebanese University
Computer Science

1997 - 1998: Baccalaureate

Maghdouche Official High School

Publications 8 publications
Charbel Rahhal Wikis sémantiques distribués sur réseaux pair-à-pair 2010

The Web 2.0 has shown the importance of collaborative systems. It has allowed to transform a community of strangers into a community of collaborators. Nowadays, many social tools such as wikis and blogs are used by large communities; they produce a large amount of information. The Semantic Web aims structuring this information in order to make it processable by machines. Many social tools evolve by integrating the Semantic Web technologies. Wikis as social tools follow this trend and evolve towards semantic wikis. The introduction of Semantic Web technologies in social tools raises a number of problems such as scalability and support for collaborative editing processes which is necessary to maintain the quality of the content. In this thesis, we address these problems through an instantiation of the optimistic replication model in the context of semantic wikis, an instantiation replicating a new data type composed of wiki pages and semantic annotations. Indeed, the optimistic replication model is based on the replication of shared objects on multiple sites and ensures their consistency. In our context, the number of sites is unknown and varies like in P2P networks. A collaborative editing system using the optimistic replication is correct if it ensures the consistency model CCI. We propose Swooki and DSMW, two instantiations of the optimistic replication model for semantic wikis that ensure the CCI consistency of the new replicated data type. Swooki is the first P2P semantic wiki. It addresses specifically the problems of scalability and fault tolerance. While DSMW allows to build a semantic friend-to-friend network and to support collaborative editing processes.

Charbel Rahhal, Hala Skaf-MolliHala, Pascal Molli SWooki: Un Wiki Sémantique sur réseau Pair-à-Pair Lavoisier 2009

Wiki systems have evolved in two different ways : semantic wikis and peer to peer wikis. Semantic wikis integrate the semantic web technologies in order to improve their structure, the search and the navigation between pages. Peer-to-peer wikis offer a support for massive collaboration, off-line editing mode and an ad-hoc collaboration. The main challenge in designing a peer-to-peer semantic wiki combining both approaches is the merge of wiki pages embedding semantic annotations. Merging algorithms used in peer-to-peer wiki systems have been designed for linear text. They do not handle semantic data. In this paper, we present SWooki the first peer-to-peer semantic wiki. SWooki combines the advantages of both semantic wikis and peer-to-peer wikis. We detail SWooki approach and its merging algorithm, we insist on its characteristics and its functionalities. We conclude by presenting its architecture and its implementation.

Charbel Rahhal, Hala Skaff-Molli, Pascal Molli, Stéphane Weiss Multi-synchronous Collaborative Semantic Wikis Springer Berlin Heidelberg 2009

Semantic wikis have opened an interesting way to mix Web 2.0 advantages with the Semantic Web approach. However, compared to other collaborative tools, wikis do not support all collaborative editing mode such as oine work or multi-synchronous editing. The lack of multi-synchronous supports in wikis is a problematic, especially, when working with semantic wikis. In these systems, it is often important to change multiple pages simultaneous in order to refactor the semantic wiki structure. In this paper, we present a new model of semantic wiki called Multi-Synchronous Semantic Wiki (MS2W). This model extends semantic wikis with multi-synchronous support that allows to create a P2P network of semantic wikis. Semantic wiki pages can be replicated on several semantic servers. The MS2W ensures CCI consistency on these pages relying on the Logoot algorithm.

Hala Skaff-Molli, Charbel Rahhal, Pascal Molli Peer-to-peer Semantic Wikis Springer Berlin Heidelberg 2009

Wikis have demonstrated how it is possible to convert a community of strangers into a community of collaborators. Semantic wikis have opened an interesting way to mix web 2.0 advantages with the semantic web approach. P2P wikis have illustrated how wikis can be deployed on P2P wikis and take advantages of its intrinsic qualities: fault-tolerance, scalability and infrastructure cost sharing. In this paper, we present the rst P2P semantic wiki that combines advantages of semantic wikis and P2P wikis. Building a P2P semantic wiki is challenging. It requires building an optimistic replication algorithm that is compatible with P2P constraints, ensures an acceptable level of consistency and generic enough to handle semantic wiki pages. The contribution of this paper is the denition of a clear model for building P2P semantic wikis. We dene the data model, operations on this model, intentions of these operations, algorithms to ensure consistency and nally we implement the SWOOKI prototype based on these algorithms.

Charbel Rahhal, Stéphane Weiss, Hala Skaf-Molli, Pascal Urso, Pascal Molli Undo in Peer-to-peer Semantic Wikis CEUR-WS.org 2009

The undo mechanism is an essential feature in collaborative editing systems. Most popular semantic wikis support a revert feature, some provide an undo feature to remove any modification at any time. However this undo feature does not always succeed. Supporting the undo mechanism for P2P semantic wikis has never been tackled. In this paper, we present an undo approach for Swooki the first P2P semantic wiki. We identify the problems to resolve in order to achieve such mechanism for P2P semantic wikis.We give the definition of the undo and the properties that must ensure. This approach allows both a revert and a permanent successful undo.

Hala Skaf-Molli, Pascal Molli, Charbel Rahhal, Hala Naja-Jazzar Collaborative Writing of XML Documents IEEE 2008

Collaborative writing is the process of two or more people working together to create a common document. People can be distributed in time, in place and across organizations. They can share writing different kinds of documents. In this paper, we focus on collaborative writing of XML documents. XML documents must be validated via a set of constraints called DTD to be considered as consistent. In cooperative writing, shared XML documents are replicated on different sites. This improves the availability of the documents. The modifications of a replica at a site are sent and integrated on all the others sites, in order to ensure the convergence of the replicas. While on each site, a replica can be validated via the DTD. After the reconciliation (also known as merging) of the different replicas, the result of merging consistent replicas may not validate the DTD. A major problem of this result, that is not possible to open a document with the tool used to edit it. To overcome this problem, we propose an automatic approach to repair inconsistency.

Hala Skaff-Molli, Claudia Ignat, Charbel Rahhal, Pascal Molli New Work Modes For Collaborative Writing ISRST 2007

In the recent years, due to the emergence of new models of production based on collaboration, collaborative writing tools started to be increasingly used by various communities. Due to great variety of groupware software, there is the need of criteria for discriminating the working modes supported by these tools. In this paper we propose a new model for the classification of collaborative writing tools. Based on our model, we categorize most popular existing collaborative tools. We also propose novel working modes that are not adopted by existing tools and that improve the process of collaboration.

Charbel Rahhal, Hala Skaf-Molli, Pascal Molli, Nishadi Desilva SemCW: Semantic Collaborative Writing using RST IEEE 2007

During collaborative writing each author works on a copy of the shared document. These copies are then merged to produce the final document. This asynchronous work is supported by several collaborative writing tools. While these tools are excellent at merging and detecting syntactic conflicts, they are not able to easily recognise semantic inconsistencies. This hinders the coherence of the document because while each individual copy might be well constructed, they may not be after the merge. To address this, we investigate the combination of the Rhetorical Structure Theory with Operational Transformation approach. In this paper, we define a data model, a set of operations to manipulate the RST structures and a set of transformation functions. A validity checker alerts the authors to areas in the text with possible semantic lapses in the merged documents.


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