Ramez Elmasri

A theory of attributed equivalence in databases with application to schema integration

The authors present a common foundation for integrating pairs of entity sets, pairs of relationship sets, and an entity set with a relationship set. This common foundation is based on the basic principle of integrating attributes. Any pair of objects whose identifying attributes can be integrated can themselves be integrated. Several definitions of attribute equivalence are presented. These definitions can be used to specify the exact nature of the relationship between a pair of attributes. Based on these definitions, several strategies for attribute integration are presented and evaluated. >

The category concept: an extension to the entity-relationship model

Abstract An enhanced version of the Entity-Relationship (ER) data model called the Entity-Category-Relationship (ECR) data model is presented. The principal extension is the introduction of the concept of a category. Categories permit the grouping of entities from different entity types according to the roles they play in a relationship, as well as the representation of ISA and generalization hierarchies. The structures of the ECR data model are defined, and a graphic representation technique for their display is presented. Language operations to define and use an ECR database are defined. Two realistic examples of the use of the ECR model for database design are demonstrated. The examples show how ECR structures can be directly mapped into relational and network structures. The definition of derived relationships on an ECR database gives the power to phrase higher order recursive queries in a first order query language.

TSQL2 language specification

This docuinent specifies a temporal extension to the SQL-92 language standard. The language is designated TSQLZ. The document is organized as follows. The next section indicates the starting point of the design, the SQL92 language. Section 4 lists the desired features on which the TSQL2 Language Design Committee reached consensus. Section 5 presents the major concepts underlying TSQL2. Compatibility with SQL-92 is the topic of Section 6. Section 7 briefly discusses how the language can be implemented. Subsequent sections specify the syntax of the language extensions.

A graphical data manipulation language for an extended entity-relationship model

A user can formulate database queries and updates graphically, by manipulating schema diagrams. The authors based the graphical data manipulation interface on the entity-relationship (ER) model because of its widespread use and increasing popularity. They use an extended ER model incorporating various forms of generalization and specialization, including subset, union and partition relationships. They call their model the extended conceptual entity-relationship or ECER model. A comparison with other graphical entity-relationship interfaces is included.<<ETX>>

Optimizing clustering algorithm in mobile ad hoc networks using genetic algorithmic approach

We show how genetic algorithms can be useful in enhancing the performance of clustering algorithms in mobile ad hoc networks. In particular, we optimize our recently proposed weighted clustering algorithm (WCA). The problem formulation along with the parameters are mapped to individual chromosomes as input to the genetic algorithmic technique. Encoding the individual chromosomes is an essential part of the mapping process; each chromosome contains information about the clusterheads and the members thereof, as obtained from the original WCA. The genetic algorithm then uses this information to obtain the best solution (chromosome) defined by the fitness function. The proposed technique is such that each clusterhead handles the maximum possible number of mobile nodes in its cluster in order to facilitate the optimal operation of the medium access control (MAC) protocol. Consequently, it results in the minimum number of clusters and hence clusterheads. Simulation results exhibit improved performance of the optimized WCA than the original WCA. Moreover, the loads among clusters are more evenly balanced by a factor of ten.

A temporal model and query language for ER databases

A temporal extension to an extended ER (entity-relationship) model is proposed. The concept of life span for entities and relationships is incorporated in the ER model. Also specified is a temporal query and update language which is an extension of the GORDAS language. The concepts of temporal Boolean expressions, temporal selection, and temporal projection are introduced, and their use in the query language is illustrated. Temporal constraints are incorporated into the ER model, and the semantics of temporal update operations is defined.<<ETX>>

Towards an infrastructure for temporal databases: report of an invitational ARPA/NSF workshop

the discussion. Specifically, an initial glossary of temporal database concepts and a. test suite of temporal queries were distributed before the workshop. Both of these document*s were amended based on the analysis and critique of the workshop. A language design committee was constituted after the workshop to develop a consensus temporal query la,nguage extension to SQL-92; this design also benefited from the discussion at the workshop. This report documents the discussions and consensus reached at the workshop. The report. reflects the conclusions rea.ched at the workshop in June, 1993 and further discussions amongst the group participants through electronic mail. In preparing this report, each group coordinator assembled ideas and prepared an initial draft, which was then reviewed by a.11 the workshop participants. The record of the deliberations of these four groups, in the following four sections, forms t.he bulk of this report. Each of these sections begins with the group’s charter and a brief snapshot of the status of the field and ends with a list of follow-on efforts. The last, section identifies the workshop pa.rticipants. The full report’ provides more discussion and many additional references t,o the literature.

Localization Systems Using Passive UHF RFID

Since gathering spatial information of objects often provides a large number of extended functions in RFID based applications, many different localization systems have been developed in recent years. Determining and estimating the physical location of tagged objects in an interrogating area is known as localization. In this paper, we study properties of passive UHF RFID systems such as the relationship between distance and RSSI (Received Signal Strength Indictor), performance variations among the same type of passive tags, and readabilities of tags. We propose a received signal strength based Localization Algorithm using passive UHF RFID system. The localization uses the k-nearest neighbor algorithm to estimate the physical position of the target tag. To improve the accuracy of the passive tag attached object location, the properties and characteristics are applied to the localization algorithm. According to the analysis of experimentation, our proposed approach shows over 34% improvement compared with the k-Nearest Neighbor algorithm with the use of single reader and a single antenna, and 13 reference tags.

Optimizing clustering algorithm in mobile ad hoc networks using simulated annealing

In this paper, we demonstrate how simulated annealing algorithm can be applied to clustering algorithms used in ad hoc networks; specifically our recently proposed weighted clustering algorithm (WCA) is optimized by simulated annealing. As the simulated annealing stands to be a powerful stochastic search method, its usage for combinatorial optimization problems was found to be applicable in our problem domain. The problem formulation along with the parameters is mapped to be an individual solution as an input to the simulated annealing algorithm. Input consists of a random set of clusterhead set along with its members and the set of all possible dominant sets chosen from a given network of N nodes as obtained from the original WCA. Simulated annealing uses this information to find the best solution defined by computing the objective function and obtaining the best fitness value. The proposed technique is such that each clusterhead handles the maximum possible number of mobile nodes in its cluster in order to facilitate the optimal operation of the MAC protocol. Consequently, it results in the minimum number of clusters and hence clusterheads. Simulation results exhibit improved performance of the optimized WCA than the original WCA.

Data model integration using the structural model

One approach to the design of a logical model for an integrated database requires each potential user or application to specify its view as a data model. An integration phase follows, where these user data models are integrated into a global database model. We address the problem of view integration when user data models are expressed using the structural model [Wi77, WE79].The structural model is built from relations in Boyce-Codd normal form [Co74]. A basic set of integrity assertions is implicit in the model. The integrity assertions are defined by classification of relations into types, and are represented by connections between relations. We will show how to integrate different representations of two related real-world entity classes.