Os tratamentos da oclusão levaram à escolha da relação cêntrica (RC) como posição de referência devido à sua reprodutibilidade, o que favorece maior precisão do diagnóstico. As interferências oclusais e os conseqüentes deslocamentos condilares entre as posições mandibulares de RC e a máxima intercuspidação habitual (MIH) têm sido revelados como parte dos fatores etiológicos das disfunções temporomandibulares. Na tentativa de melhor esclarecer o papel dos deslocamentos condilares dentro do contexto da oclusão, morfológica e funcional, como fator de risco no desenvolvimento da DTM, este estudo transversal prospectivo propôs-se a avaliar os referidos deslocamentos. A amostra foi composta por 70 participantes, não desprogramados, divididos em grupo sintomático, segundo o critério RDC/TMD, e grupo assintomático. Para avaliação dos participantes, empregaram-se modelos de gesso montados em articulador Panadent. Foram obtidos registros de cera em MIH e RC, sendo este último obediente à técnica power centric (Roth). As diferenças entre as duas posições foram medidas nos três planos do espaço, em gráficos correspondentes aos lados direito, esquerdo e transversal, avaliadas quanto à magnitude e direção e comparadas quanto à sintomatologia e o gênero pela análise de variância. A possível correlação quanto à direção do deslocamento foi avaliada pelo teste qui-quadrado de homogeneidade. Para verificar a reprodutibilidade das medidas intra e interobservador foram calculadas correlações intraclasses e índice de Dahlberg. Os resultados mostraram repetibilidade e reprodutibilidade das medidas condilares. Nos indivíduos com DTM, os deslocamentos em valores médios absolutos no plano vertical foram de 1,48 mm do lado direito (IPC vert D) e de 1,72mm do lado esquerdo (IPC vert E). No plano horizontal foram de 0,63 mm do lado direito (IPC hor D) e de 0,64 mm do lado esquerdo (IPC hor E). No plano transversal (IPC trans) o valor médio do deslocamento foi de 0,41 mm. Os valores médios absolutos dos deslocamentos condilares em indivíduos assintomáticos foram de 1,22 mm no plano vertical do lado direito (IPC vert D) e 1,30 mm do lado esquerdo (IPC vert E). No plano horizontal do lado direito (IPC hor D), os valores médios foram de 0,63 mm e do lado esquerdo (IPC hor E) 0,63 mm. No plano transversal, o valor médio do deslocamento foi de 0,23 mm (IPC trans). Na comparação entre os grupos assintomático e sintomático, constatou-se que este último apresentou valores maiores quanto ao deslocamento vertical do lado esquerdo (E) (p=0,039) e no sentido transversal (p=0,015). Observou-se também nesse grupo maior prevalência de deslocamento no sentido distal quando comparado ao grupo assintomático. Na associação entre a sintomatologia e a direção de deslocamento, verificou-se que o deslocamento condilar horizontal direito apresentou associação estatística com a sintomatologia (p=0,015). Não foram encontradas diferenças relativas à sintomatologia quanto ao gênero. O primeiro ponto de contato em RC mostrou-se localizado em sua grande maioria no segundo molar permanente, tanto no grupo sintomático (94,2%) quanto no assintomático (91,4%). / Centric relation (CR) is considered a reference position in the treatment of occlusion due to its reproducibility, thus favoring accuracy of diagnosis. Occlusal interference and consequent condylar displacement between CR and CO (centric occlusionmaxim intercuspation) have been revealed as part of the etiologic factors of temporomandibular dysfunction. In an attempt to better understand the role of condylar displacement in the context of morphologic and functional occlusion as a risk factor in TMD development, this transverse prospective study intends to evaluate the referred displacement. The sample was composed of 70 participants, not deprogrammed, divided into a symptomatic group, according to RDC/TMD criteria, and another, asymptomatic. From each subject, a wax registration in CO and CR was taken, the latter obeying the power centric technique (Roth). Cast models were mounted on a Panadent. articulator. Condylar displacement between CO and CR on three-spatial planes was measured on graphs corresponding to right, left and transverse sides, and appraised for magnitude and direction, determined by condilar position indicator instrumentation (Panadent-CPI). Analysis of variance test was used for symptom and gender comparison. The possible correlation for displacement direction and TMD was evaluated by the qui-square test of homogeneity. Inter and intraoperator reproducibility measurement error and reliability were calculated by intra-class correlations and the Dahlberg index. Low error showed high reliability and reproducibility. In TMD individuals, absolute mean values of condylar displacements in the vertical plane were 1, 48 mm on the right side (CPI vert R) and 1,72mm on the left side (CPI vert L). In the horizontal plane were 0,63mm on the right side (CPI hor R), and 0,64mm on the left (CPI hor L). In the traverse plane (IPC trans), mean value of displacement was 0,41mm. The absolute mean value of condylar displacement in asymptomatic individuals was 1,22 mm in the vertical plane on the right side (CPI vert R), and 1,30mm on the left side (CPI vert L). In the horizontal plane on the right side (CPI hor R) were 0,63mm and on the left side (CPI hor L), 0,63mm. In the tranverse plane (CPI trans) the mean value was of 0,23mm. Comparing asymptomatic and symptomatic groups it was verified that the latter presented larger values in vertical displacement on the left side (p=0,039) and in the transverse plane (p=0,015). In this group, larger displacement prevalence was also observed in distal direction when compared to the asymptomatic group. In the association between symptoms and displacement direction, it was verified that horizontal condilar displacement of the right side presented statistical association (p = 0,015). It was noted that, three-dimensional condylar displacement was found in both symptomatic and asymptomatic individuals. No correlation was found between patient gender and the presence of TMD symptoms. The initial premature contact in CR was detected, in most of the cases, on the second permanent molar, in both symptomatic (94,2%) and asymptomatic (91,4%) group.

La présente thèse de doctorat s’intéresse à la formation de la croyance en la valeur littéraire en la situation coloniale et postcoloniale, entre 1950 et 2009, en France. Pour cela, nous avons fait le choix de porter notre attention sur les trajectoires de consécration de deux auteurs algériens de langue française ayant fait l’objet d’une consécration littéraire sociologiquement objectivable, à savoir Assia Djebar (1936-) et Kateb Yacine (1929-1989). La problématique littéraire algérienne de langue française ne pouvant pertinemment être abordée au prisme de la théorie des champs de Pierre Bourdieu, nous avons fait le choix de recourir, à travers notre étude, à la notion d’institution littéraire telle que l’a notamment définie Jacques Dubois. Selon ce que nous avons alors pu observer à travers un corpus constitué d’entretiens, d’articles de presse, de discours officiels, de correspondances privées, le phénomène de consécration littéraire des deux auteurs algériens de langue française serait modélisable sous la forme de cinq étapes : la découverte, la publication, la réception critique, l’entrée dans l’univers académique, l’entrée dans l’univers de l’enseignement scolaire et universitaire. L’intérêt de cette modélisation repose principalement sur sa capacité à révéler, au-delà de la doxa littéraire, les modalités sociales ayant concouru à la formation d’une croyance en la qualité des productions textuelles données. Et, à chaque étape de la trajectoire de consécration d’Assia Djebar et de Kateb Yacine, se donnent à voir des relations fortes entre, d’une part, le littéraire et, d’autre part, l’extra-littéraire. En ce sens, l’idée couramment répandue selon laquelle la consécration d’un auteur n’aurait pour seule cause que son talent se trouve fortement remise en cause. La littérature francophone ou, plus précisément, la francophonie littéraire – dénomination sous laquelle Assia Djebar et Kateb Yacine sont régulièrement catégorisés – apparaît donc être un système réglé selon des intérêts qui, loin d’être prétendûment « purs », relèvent de logiques politique et idéologique. Engagés dans des rapports de domination symbolique et matériel dont la consécration littéraire est l’une des formes paradoxales, Assia Djebar et Kateb Yacine ont tous deux, au cours de leur trajectoire respective, mis en place des stratégies spécifiques afin de limiter la valeur instrumentale dont leurs productions textuelles ont été investies et imposer leur définition de ce que serait la littérature algérienne de langue française. / The present doctoral thesis is intersestd in the formation of the belief in literary value in colonial and postcolonial situation, between 1950 and 2009, in France. For that, we made the choice to pay our attention to the paths of recognition of two Algerian authors of French language who have been the object of an objectivable literary achievment, namely Assia Djebar (1936-) and Kateb Yacine (1929-1989). Since the Algerian literary of French language core statement can’t pertinently be approached via the prism of the fields theory by Pierre Bourdieu, we made the choice to resort, through our study, to the concept of literary insitution defined by the likes of Jacques Dubois. According to what we then could have observed through a corpus made up of talks, press articles, official discourses, private correspondences, the literary phenomenon of recognition of the two Algerian authors would be modeled in the form of five stages: the discovery, the publication, the critical reception, the entry in the academic field and the entry in the universe of secondary education. The interest of this modeling is mainly based on its capacity to reveal, beyond the literary doxa, the social methods that have contributed to the formation of a belief in the quality of the given textual productions. And, at each stage of the paths of recognition of Assia Djebar and Kateb Yacine, we can observe strong relations between, on the one hand, the literary and, on the other hand, the extra-literary. In this direction, the commonly widespread idea according to which the recognition of an author would only be based on talent is strongly questionned. The French-speaking literature or, more precisely, the literary francophonie – denomination under which Assia Djebar and Kateb Yacine are regularly categorized – thus appears to be a regulated system depending on interests far from being allegedly “pure”, but driven by ideological and political logics. Engaged in relations of symbolic domination, Assia Djebar and Kateb Yacine have both, during their respective paths, set up of specific strategies in order to limit the instrumental value of their textual productions and impose their own definition of what Algerian literature of French language truly should be.

Globalization and innovation are revolutionizing the higher education forcing to create new market trends. Different nations have their own pattern and framework of education in delivering the educational services. Educational institutions are also seeking different organizational and behavioural changes for their better future as they hunt for new financial resources, face new competition and seek greater prestige domestically and internationally. The coming future will decide which universities would survive the market trends, competition and expectations of the students (Clients). The survival-of-the-fittest paradigm framework plays a prominent role in ideas of how the higher education would be delivered to the students in future with the Instruction Technology and distance education. According to us the education trend has changed its phase of delivery of services form the management point of view to student’s point of view. Leading to delivery of educational service’s which would have more impact on student’s education, knowledge and experience within the institution. In our thesis we try to provide some information about how to support and manage the information in Virtual Organizations. We also explore the frameworks of the university and discussed a case study about the different ways of providing better support for information management resulting in delivery of best students driven services and unique facilities. We would be looking at the different aspects of the university work flows and procedures and gain an insight on the student’s expectation from the organization. This investigation would be helpful for the students to know what are the services they should expect from the universities and also helpful for management to know better the needs of the students and their needs and to develop a framework for proper execution of these services. / Pavan Kumar Yadav, S/o: B.R.Basant Kumar Yadav, Hno: 291,292, Lalbazar, Trimulgherry, Secunderabad, Andhra Pradesh, India 500015. PH: (+91)(040)27793414

Context. A huge majority of the current Internet traffic is information dissemination. Information-Centric Networking (ICN) is a future networking paradigm that focuses on global level information dissemination. In ICN, the communication is defined in terms of requesting and providing Named Data Objects (NDO). NetInf is a future networking architecture based on Information-Centric Networking principles. Objectives. In this thesis, a global routing solution for ICN has been implemented. The authority part of NDO's name is mapped to a set of routing hints each with a priority value. Multiple NDOs can share the same authority part and thus the first level aggregation is provided. The routing hints are used to forward a request for a NDO towards a suitable copy of the NDO. The second level aggregation is achieved by aggregating high priority routing hints on low priority routing hints. The performance and scalability of the routing implementation are evaluated with respect to global ICN requirements. Furthermore, some of the notable challenges in implementing global ICN routing are identified. Methods. The NetInf global routing solution is implemented by extending NEC's NetInf Router Platform (NNRP). A NetInf testbed is built over the Internet using the extended NNRP implementation. Performance measurements have been taken from the NetInf testbed. The performance measurements have been discussed in detail in terms of routing scalability. Results. The performance measurements show that hop-by-hop transport has significant impact on the overall request forwarding. A notable amount of time is taken for extracting and inserting binary objects such as routing hints at each router. Conclusions. A more suitable hop-by-hop transport mechanism can be evaluated and used with respect to global ICN requirements. The NetInf message structure can be redefined so that binary objects such as routing hints can be transmitted more efficiently. Apart from that, the performance of the global routing implementation appears to be reasonable. As the NetInf global routing solution provides two levels of aggregation, it can be scalable as well.

An extensive analysis of attribute-based encryption (ABE) in systems with resource constrained devices is performed. Two system solutions of how ABE can be performed in such systems are proposed, one where the ABE operations are performed at the resource constrained devices and one where ABE is performed at a powerful server. The system solutions are discussed with three different ABE schemes. Two of the schemes are the traditional key policy ABE (KP-ABE) and ciphertext policy ABE (CP-ABE). The third scheme is using KP-ABE to simulate CP-ABE, in an attempt to benefit from KP-ABE being computationally cheaper than CP-ABE while maintaining the intuitive way of using CP-ABE. ABE is a computationally expensive encryption method which might not be feasible to perform at the resource constrained sensors, depending on the hardware. An implementation of a CP-ABE scheme with a 128 bit security level was written and used to evaluate the feasibility of ABE on a sensor equipped with an ARM Cortex-M3 processor having 32 kB RAM and 256 kB flash. It is possible to perform CP-ABE on the sensor used in this project. The limiting factor of feasibility of ABE on the sensor is the RAM size. In this case policy sizes up to 12 attributes can be performed on the sensor. The results give an idea of the feasibility of encryption with ABE on sensors. In addition to the results several ways of improving performance of ABE on the sensor are discussed.

The Named Data Networking (NDN) is a new Internet architecture that changes the network semantic from packet delivery to content retrieval and promises benefits in areas such as content distribution, security, mobility support, and application development. While the basic NDN architecture applies to any network environment, local area networks (LANs) are of particular interest because of their prevalence on the Internet and the relatively low barrier to deployment. In this dissertation, I design NDN protocols and implement NDN software, to make NDN communication in LAN robust and efficient. My contributions include: (a) a forwarding behavior specification required on every NDN node; (b) a secure and efficient self-learning strategy for switched Ethernet, which discovers available contents via occasional flooding, so that the network can operate without manual configuration, and does not require a routing protocol or a centralized controller; (c) NDN-NIC, a network interface card that performs name-based packet filtering, to reduce CPU overhead and power consumption of the main system during broadcast communication on shared media; (d) the NDN Link Protocol (NDNLP), which allows the forwarding plane to add hop-by-hop headers, and provides a fragmentation-reassembly feature so that large NDN packets can be sent directly over Ethernet with limited MTU.

Philosophiae Doctor - PhD / Subscription-based industries have seen a massive expansion in recent decades. In this type of industry the customer has to subscribe to be able to enjoy the service; there-fore, well-de ned start and end points of the customer relationship with the service provider are known. The length of this relationship, that is the time from subscription to service cancellation, is de ned as customer survival time. Unlike transaction-based businesses, where the emphasis is on the quality of a product and customer acquisition, subscription-based businesses focus on the customer and customer retention. A customer focus requires a new approach: managing according to customer equity (the value of a rm's customers) rather than brand equity (the value of a rm's brands). The concept of customer equity is attractive and straightforward, but the implementation and management of the customer equity approach do present some challenges. Amongst these challenges is that customer asset metric - customer lifetime value (the present value of all future pro ts generated from a customer) - depends upon assumptions about the expected survival time of the customer (Bell et al., 2002; Gupta and Lehmann, 2003). In addition, managing and valuing customers as an asset require extensive data and complex modelling. The aim of this study is to illustrate, adapt and develop methods of survival analysis in analysing and estimating customer survival time in subscription-based businesses. Two particular objectives are studied. The fi rst objective is to rede ne the existing survival analysis techniques in business terms and to discuss their uses in order to understand various issues related to the customer-fi rm relationship. The lesson to be learnt here is the ability of survival analysis techniques to extract important information on customers with regard to their loyalties, risk of cancellation of the service, and lifetime value. The ultimate outcome of this process of studying customer survival time will be to understand the dynamics and behaviour of customers with respect to their risk of cancellation, survival probability and lifetime value. The results of the estimates of customer mean survival time obtained from different nonparametric and parametric approaches; namely, the Kaplan-Meier method as well as exponential, Weibull and gamma regression models were found to vary greatly showing the importance of the assumption imposed on the distribution of the survival time. The second objective is to extrapolate the customer survival curve beyond the empirical distribution. The practical motivation for extrapolating the survival curve beyond the empirical distribution originates from two issues; that of calculating survival probabilities (retention rate) beyond the empirical data and of calculating the conditional survival probability and conditional mean survival time at a speci c point in time and for a speci c time window in the future. The survival probabilties are the main components needed to calculate customer lifetime value and thereafter customer equity. In this regard, we propose a survivor function that can be used to extrapolate the survival probabilities beyond the last observed failure time; the estimation of parameters of the newly proposed extrapolation function is based completely on the Kaplan-Meier estimate of the survival probabilities. The proposed function has shown a good mathematical accuracy. Furthermore, the standard error of the estimate of the extrapolation survival function has been derived. The function is ready to be used by business managers where the objective is to enhance customer retention and to emphasise a customer-centric approach. The extrapolation function can be applied and used beyond the customer survival time data to cover clinical trial applications. In general the survival analysis techniques were found to be valuable in understanding and managing a customer- rm relationship; yet, much still needs to be done in this area of research to make these techniques that are traditionally used in medical studies more useful and applicable in business settings. / South Africa

Problem: Continuous improvement is important in modern healthcare to control increasing costs and fulfil the demand for higher quality. This requires interdisciplinary collaboration between healthcare professionals. However, these professions are seeking to maintain and improve their social status through a ‘professional project’. There are existing professional barriers based on historical privileges and boundaries, leading to nurses holding lower status. The extent to which this motivates medical professionals and nurses in particular to be involved in continuous improvement is unclear. Is it that nurses are driven to become involved in continuous improvement by their ‘professional project’, and is there any evidence that involvement in continuous improvement benefits their status? Purpose: This thesis explores (a) the effect that the ‘professional project’ of nursing, gaining relative equality with doctors, has on involvement in continuous improvement activities, and (b) how involvement in continuous improvement activities affects the status of nurses relative to doctors.  Method: This qualitative study has been performed through an interview study based on themes, on the topic of improvement in healthcare. The empirical data is gathered through semi-structured interviews conducted with professionals from Sweden, New Zealand and The Netherlands. The participants were active within Hospitals and Primary Care, and had the position of nurse, manager or doctor. Data was analysed using the Thematic Analysis approach as proposed by Braun & Clarke (2006).  Findings: The results of our research suggest that nurses’ status has certainly improved. However, rational status-seeking described by many other researchers, could be better described as ‘seeking a voice’. Nurses are driven by ambition and improving patient care, rather than seeking strict equality with doctors. Continuous improvement has given nurses the opportunity to take on more technical roles and have more input on the way medical tasks are conducted. Enhanced communication between all levels of healthcare organisations has given nurses the opportunity to show their knowledge. It has resulted in more understanding and respect by doctors of what nurses are capable of. Nurses are highly motivated to participate in continuous improvement, driven by the common logic of patient centricity. However, external factors such as limited time and financial support slow them down.

Dans cette thèse nous nous intéressons au problème d’analyse des spécifications des protocoles d’interactions des services Web orientés données. La spécification de ce type de protocoles inclut les données en plus de la signature des opérations et des contraintes d’ordonnancement des messages. L’analyse des services orientés données est complexe car l’exécution d’un service engendre une infinité d’états. Notre travail se concentre autour du problème d’existence d’une relation de simulation quand les spécifications des protocoles des services Web sont représentés en utilisant un système à transition orienté données. D’abord nous avons étudié le modèle Colombo [BCG+05]. Dans ce modèle, un service (i) échange des messages en utilisant des variables ; (ii) modifie une base de donnée partagée ; (iii) son comportement est modélisé avec un système à transition. Nous montrons que tester l’existence de la relation de simulation entre deux services Colombo non bornée est indécidable. Puis, nous considérons le cas où les services sont bornés. Nous montrons pour ce cas que le test de simulation est (i) exptime-complet pour les services Colombo qui n’accèdent pas à la base de donnée (noté ColomboDB=∅), et (ii) 2exptime-complet quand le service peut accéder à une base de donnée bornée (Colombobound). Dans la seconde partie de cette thèse, nous avons défini un modèle générique pour étudier l’impact de différents paramètres sur le test de simulation dans le contexte des services Web orientés données. Le modèle générique est un système à transition gardé qui peut lire et écrire à partir d’une base de donnée et échanger des messages avec son environnement (d’autres services ou un client). Dans le modèle générique toutes les actions sont des requêtes sur des bases de données (modification de la base de données, messages échangés et aussi les gardes). Dans ce contexte, nous avons obtenu les résultats suivant : (i) pour les services gardés sans mise à jour, le test de simulation est caractérisé par rapport à la décidabilité du test de satisfiabilité du langage utilisé pour exprimer les gardes augmenté avec une forme restrictive de négation, (ii) pour les services sans mise à jour mais qui peuvent envoyer comme message le résultat d’une requête, nous avons trouvé des conditions suffisantes d’indécidabilité et de décidabilité par rapport au langage utilisé pour exprimer l’échange de messages, et (iii) nous avons étudié le cas des services qui ne peuvent que insérer des tuples dans la base de donnée. Pour ce cas, nous avons étudié la simulation ainsi que la weak simulation et nous avons montré que : (a) la weak simulation est indécidable quand les requêtes d’insertion sont des requêtes conjonctives, (b) le test de simulation est indécidable si la satisfiabilité du langage de requête utilisé pour exprimer les insertions augmenté avec une certaine forme de négation est indécidable. Enfin, nous avons étudié l’interaction entre le langage utilisé pour exprimer les gardes et celui utilisé pour les insertions, nous exhibons une classe de service où la satisfiabilité des deux langages est décidable alors que le test de simulation entre les services qui leur sont associés ne l’est pas. / In this thesis we address the problem of analyzing specifications of data-centric Web service interaction protocols (also called data-centric business protocols). Specifications of such protocols include data in addition to operation signatures and messages ordering constraints. Analysis of data-centric services is a complex task because of the inherently infinite states of the underlying service execution instances. Our work focuses on characterizing the problem of checking a refinement relation between service interaction protocol specifications. More specifically, we consider the problem of checking the simulation preorder when service business protocols are represented using data-centric state machines. First we study the Colombo model [BCG+05]. In this framework, a service (i) exchanges messages using variables; (ii) acts on a shared database; (iii) has a transition based behavior. We show that the simulation test for unbounded Colombo is undecidable. Then, we consider the case of bounded Colombo where we show that simulation is (i) exptime-complete for Colombo services without any access to the database (noted ColomboDB=∅), and (ii) 2exptime-complete when only bounded databases are considered (the obtained model is noted Colombobound). In the second part of this thesis, we define a generic model to study the impact of various parameters on the simulation test in the context of datacentric services. The generic model is a guarded transition system acting (i.e., read and write) on databases (i.e., local and shared) and exchanging messages with its environment (i.e., other services or users). The model was designed with a database theory perspective, where all actions are viewed as queries (i.e modification of databases, messages exchanges and guards). In this context, we obtain the following results (i) for update free guarded services (i.e., generic services with guards and only able to send empty messages) the decidability of simulation is fully characterized w.r.t decidability of satisfiability of the query language used to express the guards augmented with a restrictive form of negation, (ii) for update free send services (i.e., generic services without guards and able to send as messages the result of queries over local and shared database), we exhibit sufficient conditions for both decidability and undecidability of simulation test w.r.t the language used to compute messages payloads, and (iii) we study the case of insert services (i.e., generic services without guards and with the ability of insert the result of queries into the local and the shared database). In this case, we study the simulation as well as the weak simulation relations where we show that: (i) the weak simulation is undecidable when the insertions are expressed as conjunctive queries, (ii) the simulation is undecidable if satisfiability of the query language used to express the insertion augmented with a restricted form of negation is undecidable. Finally, we study the interaction between the queries used as guards and the ones used as insert where we exhibit a class of services where satisfiability of both languages is decidable while simulation is undecidable.

Une propriété d'un objet est dite opaque pour un observateur si celui-ci ne peut déduire que la propriété est satisfaite sur la base de l'observation qu'il a de cet objet. Supposons qu'un certain de nombre de propriétés (appelées secrets) soient attachées à chaque intervenant d'un système, nous dirons alors que le système lui-même est opaque si chaque secret d'un observateur lui est opaque : il ne peut percer aucun des secrets qui lui ont été attachés. L'opacité a été étudié préalablement dans le contexte des systèmes à événements discrets où différents jeux d'hypothèses ont pu être identifiés pour lesquels on pouvait d'une part décider de l'opacité d'un système et d'autre part développer des techniques pour diagnostiquer et/ou forcer l'opacité. Cette thèse constitue la première contribution au problème de l'opacité des artefacts d'un système à flots de tâches (système workflow). Notre propos est par conséquent de formaliser ce problème en dégageant les hypothèses qui doivent être posées sur ces systèmes pour que l'opacité soit décidable. Nous indiquons quelques techniques pour assurer l'opacité d'un système. / A property (of an object) is opaque to an observer when he or she cannot deduce the property from its set of observations. If each observer is attached to a given set of properties (the so-called secrets), then the system is said to be opaque if each secret is opaque to the corresponding observer. Opacity has been studied in the context of discrete event dynamic systems where technique of control theory were designed to enforce opacity. This thesis is the first attempt to formalize opacity of artifacts in data-centric workflow systems. We motivate this problem and give some assumptions that guarantee the decidability of opacity. Some techniques for enforcing opacity are indicated.