Cem Evrendilek

• Doctor of Philosophy
• Professor at İzmir University of Economics

Given an edge weighted tree T(V, E), rooted at a designated base vertex \(r \in V\), and a color from a set of colors \(C=\{1,\ldots ,k\}\) assigned to every vertex \(v \in V\), All Colors Shortest Path problem on trees (ACSP-t) seeks the shortest, possibly non-simple, path starting from r in T such that at least one node from every distinct color...

Localization is an essential service in wireless sensor networks. Trilateration is a commonly used solution to range based localization for providing such services. It might be, however, impossible to localize the entire network at once using trilateration due to low connectivity on sparse deployments. In such scenarios, a mobile beacon with a know...

In this paper, we address the problem of covering a given set of points on the plane with minimum and/or maximum area orthogonally convex polygons. It is known that the number of possible orthogonally convex polygon covers can be exponential in the number of input points. We propose, for the first time, an algorithm to construct either the maximum...

All Colors Shortest Path problem defined on an undirected graph aims at finding a shortest, possibly non-simple, path where every color occurs at least once, assuming that each vertex in the graph is associated with a color known in advance. To the best of our knowledge, this paper is the first to define and investigate this problem. Even though th...

Most large organizations, such as corporations, are hierarchical organizations. In hierarchical organizations each entity in the organization, except the root entity, is a sub-part of another entity. In this paper we study the task assignment problem to the entities of tree-like hierarchical organizations. The inherent tree structure introduces an...

We address the problem of covering points with orthogonal polygons. Specifically, given a set of nn points in the plane, we investigate the existence of an orthogonal polygon such that there is a one-to-one correspondence between the points and the edges of the polygon. In an earlier paper, we have shown that constructing such a covering with an or...

Many applications in wireless networks depend on accurate localization services to operate properly. Trilateration is a widely used range-based localization method that can operate in polynomial time, given that the distance measurements are precise. However in real-world, range measurements tend to have errors due to internal and external factors....

Location discovery, especially in mobile environments, has recently become the key component of many applications. Accurate location discovery, particularly in safety critical applications using autonomous robots or unmanned vehicles, however, is still an open problem. Existing popular methods either heavily rely on the use of global positioning sy...

Recent developments, especially in wireless and mobile networks, have enabled the use of location based services in many application areas. Accurate location discovery, however, is still an open problem. A widely used and practical localization method is trilateration. However, trilateration works best when exact range measurements are available, w...

In this paper, we address the problem of covering points with orthogonally convex polygons. In particular, given a point set of size n on the plane, we aim at finding if there exists an orthogonally convex polygon such that each edge of the polygon covers exactly one point and each point is covered by exactly one edge. We show that if such a polygo...

We address the problem of covering points with orthogonal polygons. Specifically, given a set of n grid-points in the plane each designated in advance with either a horizontal or vertical reading, we investigate the existence of an orthogonal polygon covering these n points in such a way that each edge of the polygon covers exactly one point and ea...

Finite Element Method (FEM) is a well known technique extensively studied for spatial and temporal modeling of environmental processes, weather prediction computations, and intelligent signal processing for wireless sensors. The need for huge computational power arising in such applications to simulate physical phenomenon correctly mandates the use...

The object-oriented database management systems store references to objects (implicit joins, precomputed joins), and use path expressions in query languages. One way of executing path expressions is pointer chasing of precomputed joins. However it has been previously shown that converting implicit joins to explicit joins during the optimization pha...

The increasing availability of the Internet has allowed tremendous amounts of data to be stored and accessed by the users of the Web. This, in turn, has brought up an expectation to access data widely distributed in nature in an efficient manner. The type of access to such data, however, is currently in the form of non-database facilities. It is co...

METU Object-Oriented DBMS1 includes the implementation of a database kernel, an object-oriented SQL-like language and a graphical user interface. Kernel functions are divided between a SQL Interpreter and a C++ compiler. Thus the interpretation of functions are avoided increasing the efficiency of the system. The compiled by C++ functions are used...

this paper is organized as follows. The architecture of the MIND system is described in Section 2. Section 3 presents the infrastructure of the system. The design decisions and experiences in developing generic Database Object implementations for various DBMSs are also discussed in this section. Section 4 describes the schema integration in MIND. T...

: In this paper we describe a formal method to define an object-oriented data model. For a long time object-oriented paradigm had been criticized for the lack of a formal foundation. Our data model captures all of the basic concepts of the objectoriented paradigm. In this paper we define a lattice structure to explain the semantics of classes, type...

Abstract A multidatabase system (MDBS) allows the users to simultaneously access autonomous, heterogeneous databases using a single data model and a query language. This provides for achieving interoperability among heterogeneous, federated DBMSs. In this paper, we describe the interoperability infrastructure of a multidatabase system, namely METU...

A multidatabase system (MDBS) allows the users to simultaneously access heterogeneous,and autonomous databases using an integrated schema and a single global query language. The query optimization problem in MDBSs is quite different from the query optimization problem in distributed homogeneous databases due to schema heterogeneity and autonomy of...

In designing a complex information system, it is not always possible for the user to be able to specify all his requirements prior to the design. It is, therefore, necessary to follow a goal driven design process. Such a design necessitates to put forward a generic goal architecture based on both the generic and some system specific characteristics...

The purpose of this chapter is to present and describe a methodology for the elicitation and analysis of user requirements in designing an information system. For the reasons given in Chapter 1, the requirements capture will be for a military organization which we shall take as an example in this book.

Having defined the architecture and configuration including the dimensioning of the C3I system we now have to cost it in terms of capital and recurring costs and draw up an implementation plan over a time scale consistent with the user requirements and within funding and other constraints set at the beginning of the design process (see Sec. 1.5). I...

A fundamental assumption made in designing a C3I system, may it be for civilian or military applications, is that it will meet all the requirements of its user(s) and that it will have a distributed architecture to correspond to the geographically distributed user organization. It is vitally important that the system is always ready to serve its us...

As technological advances make information more available and more vulnerable, awareness of information security issues such as personal privacy, computer fraud and legislation, and national security related concerns are brought to light. A meaningful information security program depends on the support from the top management of the organization. I...

The development and fielding of any new high-tech system requires a very close dialogue and inter-play between the user community and industry.

The final step, of the three-step methodology prescribed in Chapter 1, in transforming user requirements into an operational system is to derive the actual hardware and software configurations from the system architecture discussed in Chapter 5. This transformation covers the selection of the hardware and software products in accordance with the ar...

Having defined the Reference Model (RM) * which, as stated previously, is the primary tool for expressing functional and cost related goals in technical terms we now come to the second step of the design methodology, which is the architectural design and this comprises the process of selecting available technologies for each of the functional eleme...

Preface. 1. Introduction. 2. Methodology for Collecting and Analyzing User Requirements: Mission-Oriented Analysis. 3. General System Outline: Goal Architecture. 4. Reference Model. 5. System Architecture Design. 6. System Configuration. 7. Security Architecture. 8. System Management. 9. System Costing and Implementation Plan. Epilogue.

METU Interoperable DBMS (MIND) is a multidatabase system based on OMG's distributed object management architecture. It is implemented on top of a CORBA compliant ORB, namely, DEC's ObjectBroker. In MIND, all local databases are encapsulated in a generic database object. The interface of the generic database object is defined in CORBA IDL and multip...

METU INteroperable Database System (MIND) is a multidatabase system that aims at achieving interoperability among heterogeneous, federated DBMSs. MIND architecture if based on OMG distributed object management model. It is implemented on top of a CORBA compliant ORB, namely, ObjectBroker. MIND provides users a single ODMG-93 compliant common data m...

In conventional object oriented programming languages, objects are transient, that is they are destroyed upon program termination. Storing objects using explicit file access methods may cause objects to lose their manipulation and access semantics since the objects with different declarations may have the same storage representation. In this work p...

and Sevgi Foundation, Turkey) is a multidatabase system based on OMG's (OMG is a registered trademark, and CORBA, ORB, OMG IDL, Object Request Broker are trademarks of OMG) distributed object management architecture. It is implemented on top of a CORBA compliant ORB, namely, DEC's ObjectBroker (ObjectBroker is a registered trademark of DE...

In the mobile wireless computing environment of the future a large number of users equipped with low powered palm-top machines will query databases over the wireless communication channels. Palmtop based units will often be disconnected for prolonged ...

OODBMSs need more than declarative query languages and programming languages as their interfaces since they are designed and implemented for complex applications requiring more advanced and easy to use visual interfaces. We have developed a complete programming environment for this purpose, called MoodView. MoodView translates all the user actions...

this paper is organized as follows. The architecture of the MIND system is described in Section 2. Section 3 presents the infrastructure of the system. The design decisions and experiences in developing generic Database Object implementations for various DBMSs are also discussed in this section. Section 4 describes the schema integration in MIND. T...

1. Introduction One way of achieving interoperability among heterogeneous, federated DBMSs is through a multidatabase system that supports a single common data model and a single global query language on top of different types of existing systems. The global schema of a multidatabase system is the result of a schema integration of the schemas expor...

In this paper, we present a new clustering algorithm called the High Fan Out algorithm and then give the performance comparison of the High Fan Out (HFO) algorithm, Kernighan-Lin based algorithms, and the Probability Ranking Partitioning algorithm for a persistent C++(C**) implementation in a single user environment where the global request stream...

A SQL-like object-oriented query language is implemented on Exodus Storage Manager with an original query optimization strategy based on the object-oriented features of the language. For this purpose the selectivity of a path expression, cost of forward and backward traversals are calculated, and join sizes are estimated. An original strategy is de...

A Distributed Object Management (DOM) architecture, when used as the infrastructure of a multidatabase system, not only enables easy and flexible interoperation of DBMSs, but also facilitates interoperation of the multidatabase system with other repositories that do not have DBMS capabilities. This is an important advantage, since most of data stil...

A SQL-like object-oriented query language is implemented on Exodus Storage Manager with an original query optimization strategy based on the object-oriented features of the language. For this purpose the selectivity of a path expression, cost of forward and backward traversals are calculated, and join sizes are estimated. An original strategy is de...