ABSTRACT Nearest neighbors queries are commonly used in location based services. This paper focus... more ABSTRACT Nearest neighbors queries are commonly used in location based services. This paper focuses on enhancing their processing based on indexing structures. Indexes, like R-trees, cannot avoid backtracking to process them. This feature weakens suitability of such an index to several data access modes within mobile environments. To meet needs of these environments, we propose a novel index called VN-tree (Voronoi-Neighbors tree), based on the Voronoi diagram and its dual graph (the Delaunay Triangulation) of the candidate points of interest. VN-tree adopts a non-overlapping partitioning scheme and supports backtracking-free search algorithms to answer several types of queries. In particular, processing continuous nearest neighbor queries is a straightforward use of VN-tree. We conduct various experiments to compare VN-tree with R*-tree as in-memory indexes in the on-demand data access mode. Main results show that VN-tree consistently provides outstanding performances.
Nowadays, with the widespread deployment of smartphones the major challenge is to provide ubiquit... more Nowadays, with the widespread deployment of smartphones the major challenge is to provide ubiquitous services, in particular, the pedestrian navigation service that rely greatly on both the positioning technology (e.g., WiFi, Bluetooth, etc.) and the positioning technique. In this paper, we propose a positioning handoff decision algorithm based on service parameters and user requirements to ensure a seamless and continuous switch process between heterogeneous available positioning technologies. The proposed algorithm starts by identifying the key parameters acting on the selection procedure, then, computes criteria weights by applying the fuzzy analytic hierarchy process -- AHP and finally, conducts to the best suitable positioning technology using a specific ranking function that always prefers the most accurate positioning technique. We end this paper by comparing our proposal with two different multicriteria decision making -- MCDM methods: the technique for order preference by similarity to the ideal solution -- TOPSIS and the simple additive weighting -- SAW approach.
Nowadays, with the development of ubiquitous and pervasive computing, pedestrian navigation syste... more Nowadays, with the development of ubiquitous and pervasive computing, pedestrian navigation systems are gaining significant momentum for location based services. To perform a seamless navigation service, a mobile unit MU is capable of capturing several positioning technologies, running simultaneously or independently according to user's needs. This paper proposes a dynamic selection algorithm to evaluate and determine the best positioning technology from available candidates, in the process of switching between technologies during an indoor outdoor pedestrian navigation procedure. This choice depends on many factors related to user preferences and service parameters such as power consumption, positioning accuracy and the number of visible GPS satellites. The proposed algorithm is based on a fuzzy analytic hierarchy process -- AHP as the most wellknown multiple criteria decision making -- MCDM approach that provides a description and a manipulation of several criteria information to infer the need for initializing the switch process. The introduced algorithm employs the AHP method to calculate criteria weight and define a selection function that ensures the determination of the convenient positioning technology.
Quite recently, considerable attention has been paid to pedestrian navigation services, since the... more Quite recently, considerable attention has been paid to pedestrian navigation services, since they provide people with guidance and tracking information everywhere especially in an unfamiliar environment. In the literature, indoor and outdoor navigation has been widely investigated. However, studies on the continuity of pedestrian navigation service, still lacking. This paper presents a novel positioning technology selection algorithm able to integrate the pedestrian dead reckoning (PDR) technique, for short-term, through the navigation process either to improve the calculation of the mobile unit's (MU) position and/or to maintain the continuity of the service. The integration of the PDR is inferred based on the fuzzy logic approach. In fact, the proposed algorithm defines a fuzzy variable called “margin” which identifies four different states, namely, confidence, intermediate, confusion and critic. The PDR technique is only incorporated in the last two states in two ways: either fused with the used radio frequency (RF) positioning technology or stand-alone if no RF technology is available. The algorithm performance is evaluated based on an empirical study.
With the advent of wearable and smartphone technologies, the need for pedestrian navigation servi... more With the advent of wearable and smartphone technologies, the need for pedestrian navigation services has increased over the last decade. Outdoor, the GPS remains currently the navigation standard. However, indoor navigation is in a development stage and suffers from many limitations, mainly related to the used positioning technologies and techniques and to the problem of finding the path from the origin to the destination. Previous studies have been limited to either positioning services or navigation services within a single floor building. The focus of this work is to develop a multi-floor pedestrian navigation service. This prototype is composed of two main modules. First, a positioning module, is conceived to compute the mobile unit (MU) position using the pedestrian dead reckoning (PDR) and the received signal strength indicator (RSSI) fingerprinting positioning techniques. Second, a navigation module, is designed to identify the rooms’ numbers inside a building and to generate the graph for the whole building. The performance of our prototype is evaluated in the building IT Zentrum/International House on the campus of the University of Passau in Germany.
ABSTRACT The emergence of pervasive computing in our everyday life supposes that the data necessa... more ABSTRACT The emergence of pervasive computing in our everyday life supposes that the data necessary to the operation of the majority of our essential services in various fields of life will be managed by these systems. Thus, their dependability became a major concern. But, dependability issues have not been well explored so far in pervasive computing research. Pervasive environments are highly complex, heterogeneous and geographically dispersed. As a result, current means and facets of dependability do not address the needs of these systems. A solution to achieve this goal should be to adopt a dependability approach based on survivability in pervasive environments. But, the survivability suffers from a remarkable lack of suitable and mature methods for using it in practice. In this paper, we focus on achieving survivability in pervasive environments. First, we introduce a formal survivability model based on a rigorous definition of the concept of acceptable service and a method for calculating the degree of survivability of the system. Then, we present the basis for a new approach to adapt the system in adverse operation environment to comply with its survivability specification. To fix ideas, a case study in pervasive healthcare is presented.
Mobile query processing is, actually, a very active research field. Range and nearest neighbor qu... more Mobile query processing is, actually, a very active research field. Range and nearest neighbor queries are common types of queries in spatial databases and location based services (LBS). In this paper, we focus on finding nearest neighbors of a query point within a certain distance range. An example of query, frequently met in LBS, is “Find all the nearest gas stations within 2 miles neighborhood of his/her current location”. We propose two approaches for answering such queries. Both are based on a recent indexing technique called N-tree. The first one is a branch and bound approach, whereas the second, called ‘neighborhoods scanning’, is based on a variant of N-tree, Leaves-Linked N-tree (LLN-tree). LLN-tree is an index tree structure that avoids visiting multiple paths during range search. Both techniques are presented, illustrated and evaluated. Experiments show that the latter approach outperforms the former in response time and disk access as well.
ABSTRACT The optimization of general queries in a distributed database management system is an im... more ABSTRACT The optimization of general queries in a distributed database management system is an important and challenging research issue. The problem is to find an optimal evaluation strategy for a given general query. In this paper, we propose an approach based on a combination of join and parallel semijoin operations to minimize the amount of data transmission in distributed query processing. First, we describe an efficient distributed query processing strategy using only semijoins. This strategy selects an optimal set instead of a sequence of semijoins to be executed in parallel in three phases: a projection phase, a transmission phase and a reduction phase. Then, we apply a sequence of joins as reducers for query processing. Furthermore, we consider the problem of finding an optimal general sequence that fully reduces a general join query graph. We present a new method that combines parallel and sequential semijoins. We report on experiments that show that our approach based on parallel semijoins is not only efficient but also effective in reducing the total amount of data transmission required to process distributed queries.
2016 IEEE 30th International Conference on Advanced Information Networking and Applications (AINA), 2016
Nowadays, with the widespread deployment of smartphones the major challenge is to provide ubiquit... more Nowadays, with the widespread deployment of smartphones the major challenge is to provide ubiquitous services, in particular, the pedestrian navigation service that rely greatly on both the positioning technology (e.g., WiFi, Bluetooth, etc.) and the positioning technique. In this paper, we propose a positioning handoff decision algorithm based on service parameters and user requirements to ensure a seamless and continuous switch process between heterogeneous available positioning technologies. The proposed algorithm starts by identifying the key parameters acting on the selection procedure, then, computes criteria weights by applying the fuzzy analytic hierarchy process -- AHP and finally, conducts to the best suitable positioning technology using a specific ranking function that always prefers the most accurate positioning technique. We end this paper by comparing our proposal with two different multicriteria decision making -- MCDM methods: the technique for order preference by similarity to the ideal solution -- TOPSIS and the simple additive weighting -- SAW approach.
In this paper, we propose an approach based on a combination of join and parallel semijoin operat... more In this paper, we propose an approach based on a combination of join and parallel semijoin operations to minimize the amount of data transmission in distributed query processing. First, we describe an efficient distributed query processing strategy using only semijoins. This strategy selects an optimal set instead of a sequence of semijoins to be executed in parallel. Then, we present a new method that combines parallel semijoins and sequential joins. Our results show that the approach based on parallel semijoins is not only efficient but also effective in reducing the communication cost required for data transmission.
ABSTRACT Nearest neighbors queries are commonly used in location based services. This paper focus... more ABSTRACT Nearest neighbors queries are commonly used in location based services. This paper focuses on enhancing their processing based on indexing structures. Indexes, like R-trees, cannot avoid backtracking to process them. This feature weakens suitability of such an index to several data access modes within mobile environments. To meet needs of these environments, we propose a novel index called VN-tree (Voronoi-Neighbors tree), based on the Voronoi diagram and its dual graph (the Delaunay Triangulation) of the candidate points of interest. VN-tree adopts a non-overlapping partitioning scheme and supports backtracking-free search algorithms to answer several types of queries. In particular, processing continuous nearest neighbor queries is a straightforward use of VN-tree. We conduct various experiments to compare VN-tree with R*-tree as in-memory indexes in the on-demand data access mode. Main results show that VN-tree consistently provides outstanding performances.
Nowadays, with the widespread deployment of smartphones the major challenge is to provide ubiquit... more Nowadays, with the widespread deployment of smartphones the major challenge is to provide ubiquitous services, in particular, the pedestrian navigation service that rely greatly on both the positioning technology (e.g., WiFi, Bluetooth, etc.) and the positioning technique. In this paper, we propose a positioning handoff decision algorithm based on service parameters and user requirements to ensure a seamless and continuous switch process between heterogeneous available positioning technologies. The proposed algorithm starts by identifying the key parameters acting on the selection procedure, then, computes criteria weights by applying the fuzzy analytic hierarchy process -- AHP and finally, conducts to the best suitable positioning technology using a specific ranking function that always prefers the most accurate positioning technique. We end this paper by comparing our proposal with two different multicriteria decision making -- MCDM methods: the technique for order preference by similarity to the ideal solution -- TOPSIS and the simple additive weighting -- SAW approach.
Nowadays, with the development of ubiquitous and pervasive computing, pedestrian navigation syste... more Nowadays, with the development of ubiquitous and pervasive computing, pedestrian navigation systems are gaining significant momentum for location based services. To perform a seamless navigation service, a mobile unit MU is capable of capturing several positioning technologies, running simultaneously or independently according to user's needs. This paper proposes a dynamic selection algorithm to evaluate and determine the best positioning technology from available candidates, in the process of switching between technologies during an indoor outdoor pedestrian navigation procedure. This choice depends on many factors related to user preferences and service parameters such as power consumption, positioning accuracy and the number of visible GPS satellites. The proposed algorithm is based on a fuzzy analytic hierarchy process -- AHP as the most wellknown multiple criteria decision making -- MCDM approach that provides a description and a manipulation of several criteria information to infer the need for initializing the switch process. The introduced algorithm employs the AHP method to calculate criteria weight and define a selection function that ensures the determination of the convenient positioning technology.
Quite recently, considerable attention has been paid to pedestrian navigation services, since the... more Quite recently, considerable attention has been paid to pedestrian navigation services, since they provide people with guidance and tracking information everywhere especially in an unfamiliar environment. In the literature, indoor and outdoor navigation has been widely investigated. However, studies on the continuity of pedestrian navigation service, still lacking. This paper presents a novel positioning technology selection algorithm able to integrate the pedestrian dead reckoning (PDR) technique, for short-term, through the navigation process either to improve the calculation of the mobile unit's (MU) position and/or to maintain the continuity of the service. The integration of the PDR is inferred based on the fuzzy logic approach. In fact, the proposed algorithm defines a fuzzy variable called “margin” which identifies four different states, namely, confidence, intermediate, confusion and critic. The PDR technique is only incorporated in the last two states in two ways: either fused with the used radio frequency (RF) positioning technology or stand-alone if no RF technology is available. The algorithm performance is evaluated based on an empirical study.
With the advent of wearable and smartphone technologies, the need for pedestrian navigation servi... more With the advent of wearable and smartphone technologies, the need for pedestrian navigation services has increased over the last decade. Outdoor, the GPS remains currently the navigation standard. However, indoor navigation is in a development stage and suffers from many limitations, mainly related to the used positioning technologies and techniques and to the problem of finding the path from the origin to the destination. Previous studies have been limited to either positioning services or navigation services within a single floor building. The focus of this work is to develop a multi-floor pedestrian navigation service. This prototype is composed of two main modules. First, a positioning module, is conceived to compute the mobile unit (MU) position using the pedestrian dead reckoning (PDR) and the received signal strength indicator (RSSI) fingerprinting positioning techniques. Second, a navigation module, is designed to identify the rooms’ numbers inside a building and to generate the graph for the whole building. The performance of our prototype is evaluated in the building IT Zentrum/International House on the campus of the University of Passau in Germany.
ABSTRACT The emergence of pervasive computing in our everyday life supposes that the data necessa... more ABSTRACT The emergence of pervasive computing in our everyday life supposes that the data necessary to the operation of the majority of our essential services in various fields of life will be managed by these systems. Thus, their dependability became a major concern. But, dependability issues have not been well explored so far in pervasive computing research. Pervasive environments are highly complex, heterogeneous and geographically dispersed. As a result, current means and facets of dependability do not address the needs of these systems. A solution to achieve this goal should be to adopt a dependability approach based on survivability in pervasive environments. But, the survivability suffers from a remarkable lack of suitable and mature methods for using it in practice. In this paper, we focus on achieving survivability in pervasive environments. First, we introduce a formal survivability model based on a rigorous definition of the concept of acceptable service and a method for calculating the degree of survivability of the system. Then, we present the basis for a new approach to adapt the system in adverse operation environment to comply with its survivability specification. To fix ideas, a case study in pervasive healthcare is presented.
Mobile query processing is, actually, a very active research field. Range and nearest neighbor qu... more Mobile query processing is, actually, a very active research field. Range and nearest neighbor queries are common types of queries in spatial databases and location based services (LBS). In this paper, we focus on finding nearest neighbors of a query point within a certain distance range. An example of query, frequently met in LBS, is “Find all the nearest gas stations within 2 miles neighborhood of his/her current location”. We propose two approaches for answering such queries. Both are based on a recent indexing technique called N-tree. The first one is a branch and bound approach, whereas the second, called ‘neighborhoods scanning’, is based on a variant of N-tree, Leaves-Linked N-tree (LLN-tree). LLN-tree is an index tree structure that avoids visiting multiple paths during range search. Both techniques are presented, illustrated and evaluated. Experiments show that the latter approach outperforms the former in response time and disk access as well.
ABSTRACT The optimization of general queries in a distributed database management system is an im... more ABSTRACT The optimization of general queries in a distributed database management system is an important and challenging research issue. The problem is to find an optimal evaluation strategy for a given general query. In this paper, we propose an approach based on a combination of join and parallel semijoin operations to minimize the amount of data transmission in distributed query processing. First, we describe an efficient distributed query processing strategy using only semijoins. This strategy selects an optimal set instead of a sequence of semijoins to be executed in parallel in three phases: a projection phase, a transmission phase and a reduction phase. Then, we apply a sequence of joins as reducers for query processing. Furthermore, we consider the problem of finding an optimal general sequence that fully reduces a general join query graph. We present a new method that combines parallel and sequential semijoins. We report on experiments that show that our approach based on parallel semijoins is not only efficient but also effective in reducing the total amount of data transmission required to process distributed queries.
2016 IEEE 30th International Conference on Advanced Information Networking and Applications (AINA), 2016
Nowadays, with the widespread deployment of smartphones the major challenge is to provide ubiquit... more Nowadays, with the widespread deployment of smartphones the major challenge is to provide ubiquitous services, in particular, the pedestrian navigation service that rely greatly on both the positioning technology (e.g., WiFi, Bluetooth, etc.) and the positioning technique. In this paper, we propose a positioning handoff decision algorithm based on service parameters and user requirements to ensure a seamless and continuous switch process between heterogeneous available positioning technologies. The proposed algorithm starts by identifying the key parameters acting on the selection procedure, then, computes criteria weights by applying the fuzzy analytic hierarchy process -- AHP and finally, conducts to the best suitable positioning technology using a specific ranking function that always prefers the most accurate positioning technique. We end this paper by comparing our proposal with two different multicriteria decision making -- MCDM methods: the technique for order preference by similarity to the ideal solution -- TOPSIS and the simple additive weighting -- SAW approach.
In this paper, we propose an approach based on a combination of join and parallel semijoin operat... more In this paper, we propose an approach based on a combination of join and parallel semijoin operations to minimize the amount of data transmission in distributed query processing. First, we describe an efficient distributed query processing strategy using only semijoins. This strategy selects an optimal set instead of a sequence of semijoins to be executed in parallel. Then, we present a new method that combines parallel semijoins and sequential joins. Our results show that the approach based on parallel semijoins is not only efficient but also effective in reducing the communication cost required for data transmission.
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Papers by Faiza Najjar