Technical Reports Published in 2002

BU-CE-0201: PDF

A Histogram-Based Approach for Object-Based Query-by-Shape-and-Color in Multimedia Databases

Ediz Şaykol, Uğur Güdükbay and Özgür Ulusoy

Considering the fact that most of the multimedia database systems include querying by object features, a novel approach for color and shape querying and retrieval is proposed. The approach is histogram-based and it is supported by an auxiliary object extraction tool in the query-by-feature component of a multimedia database system. The object extraction tool is semi-automatic, hence it can successfully capture salient object regions for most of the images and/or video frames. The use of the object extraction tool facilitates object-based querying of color and shape content. In the histogram-based approach, the color and shape can be integrated to improve the performance of querying. It is shown through performance experiments that the histogram-based approach overcomes the deficiencies of the existing methods for querying by shape. The evaluation of the effectiveness and the robustness of the histogram-based approach is also presented via performance experiments.

Keywords: Histogram-based approach, query-by-shape, query-by-color, histogram comparison, object-based querying, kinematics model for polygon simplification, random noise model, retrieval effectiveness.

BU-CE-0202: PDF

Componentwise Bounds for Nearly Completely Decomposable Markov Chains using Stochastic Comparison and Reordering

Nihal Pekergin, Tuğrul Dayar, and Denizhan N. Alparslan

This paper presents an improved version of a componentwise bounding algorithm for the state probability vector of nearly completely decomposable Markov chains, and on an application it provides the first numerical results with the type of algorithm discussed. The given two-level algorithm uses aggregation and stochastic comparison with the strong stochastic (st) order. In order to improve accuracy, it employs reordering of states and a better componentwise probability bounding algorithm given st upper- and lower-bounding probability vectors. A thorough analysis of the two-level algorithm from the point of view of irreducibility is provided. Results in sparse storage show that there are cases in which the given algorithm proves to be useful.

BU-CE-0203: PDF

Permuting Sparse Rectangular Matrices into Block-Diagonal Form

Cevdet Aykanat, Ali Pınar, and Ümit V. Çatalyürek

This work investigates the problem of permuting a sparse rectangular matrix into block diagonal form. Block diagonal form of a matrix grants an inherent parallelism for the solution of the deriving problem, which has been recently investigated in the context of mathematical programming, LU factorization and QR factorization. We propose bipartite graph and hypergraph models to represent the nonzero structure of a matrix, which reduce the permutation problem to those of graph partitioning by vertex separator and hypergraph partitioning, respectively. Besides proposing the models to represent sparse matrices and investigating related combinatorial problems, we provide a detailed survey of relevant literature to bridge the gap between different societies, investigate existing techniques for partitioning and propose new ones, and finally present a thorough empirical study of these techniques. Our experiments on a wide range of matrices, using state-of-the-art graph and hypergraph partitioning tools MeTiS and PaToH, revealed that the proposed methods yield very effective solutions both in terms of solution quality and runtime.

BU-CE-0204: PDF

Efficient Parallel Frequency Mining Based On a Novel Top-Down Partitioning Scheme for Transactional Data (M. Sc. Thesis)

Eray Ozkural

In recent years, large quantities of data have been amassed with advances in data acquisition capabilities. Automated detection of useful information is required for vast data obtained from scientific and business domains. Data Mining is the application of efficient algorithmic solutions on a variety of immense data for such knowledge discovery. Frequency mining discovers all frequent patterns in a transaction or relational database and it comprises the core of several data mining algorithms such as association rule mining and sequence mining. Frequency pattern discovery has become a challenge for parallel programming since it is a highly complex operation on huge datasets demanding efficient and scalable algorithms. In this thesis, we propose a new family of parallel frequency mining algorithms. We introduce a novel transaction set partitioning scheme that can be used to divide the frequency mining task in a top-down fashion. The method operates on the graph of frequent patterns with length two (GF2) from which a graph partitioning by vertex separator (GPVS) is mapped to a two-way partitioning on the transaction set. The two parts obtained can be mined independently and therefore can be utilized for concurrency. In order for this property to hold, there is an amount of replication dictated by the separator in GF2 which is minimized by the GPVS algorithm. A k-way partitioning is derived from recursive application of 2-way partitioning scheme which is used in the design of a generic parallel frequency mining algorithm. First we compute GF2 in parallel, succeeding that we designate a k-way partitioning of the database for k processors with a parallel recursive procedure. The database is redistributed such that each processor is assigned one part. Subsequent mining proceeds simultaneously and independently at each processor with a given serial mining algorithm. A complete implementation in which we employ FP-Growth as the sequential algorithm has been achieved. The performance study of the algorithm on a Beowulf system demonstrates favorable performance for synthetic databases. For hard instances of the problem, we have gained approximately twice the speedup of a state-of-the-art algorithm. We also present a correction and optimization to FP-Growth algorithm.

Keywords: Parallel Data Mining, Frequency Mining

BU-CE-0205: PDF

ARG: A Tool for Automatic Report Generation

Murat Karakaya and H. Altay Güvenir

The expansion of on-line text with the rapid growth of the Internet imposes utilizing Data Mining techniques to reveal the information embedded in these documents. Therefore text classification and text summarization are two of the most important application areas. In this work, we attempt to integrate these two techniques to help the user to compile and extract the information that is needed. Basically, we propose a two-phase algorithm in which the paragraphs in the documents are first classified according to given topics and then each topic is summarized to constitute the automatically generated report.

Keywords: Data mining, text summarization, text classification, automatic report generation.

BU-CE-0206: PDF

Diagnosis of Gastric Carcinoma Tumors by Classification on Feature Projections

H. Altay Güvenir, Narin Emeksiz and Necati Örmeci

A new classification algorithm, called BCFP (for Benefit Maximizing Classifier on Feature Projections), is developed and applied to the problem of diagnosis of gastric carcinoma tumors. The domain contains records of patients with known diagnosis through gastroscopy results. Given a training set of such records, the BCFP classifier learns how to differentiate a new case in the domain. BCFP represents a concept in the form of feature projections on each feature dimension separately. Classification in the BCFP algorithm is based on a voting among the individual predictions made on each feature. In the gastric carcinoma tumors domain, a lesion can be an indicator of one of nine different levels of gastric carcinoma tumors, from early to late stages. The benefit of correct classification of early levels is much more than that of late cases. Also, the cost of wrong classification is not symmetric. In the training phase, the BCFP algorithm learns classification rules that maximize the benefit of classification. In the querying phase, using these rules, the BCFP algorithm tries to make a prediction maximizing the benefit. A genetic algorithm is applied to select the relevant features. The performance of the BCFP classifier is evaluated in terms of accuracy and running time. It is also compared with human experts.

Keywords: Machine learning, voting, multi-class classification, benefit maximization, feature selection, gastric carcinoma tumors.

BU-CE-0207: PDF

Predicting Next Page Access by Time Length Reference in the Scope of Effective Use of Resources (M. Sc. Thesis)

Berkan Yalçınkaya

Access log file is like a box of treasure waiting to be exploited containing valuable information for the web usage mining system. We can convert this information hidden in the access log files into knowledge by analyzing them. Analysis of web server access data can help understand the user behavior and provide information on how to restructure a web site for increased effectiveness, thereby improving the design of this collection of resources. We designed and developed a new system in this thesis to make dynamic recommendation according to the interest of the visitors by recognizing them through the web. The system keeps all user information and uses this information to recognize the other user visiting the web site. After the visitor is recognized, the system checks whether she/he has visited the web site before or not. If the visitor has visited the web site before, it makes recommendation according to his/her past actions. Otherwise, it makes recommendation according to the visitors coming from the parent domain. Here, "parent domain" identifies the domain in which the identity belongs to. For instance, "" is the parent domain of the "". The importance of the pages that the visitors are really interested in and the identity information forms the skeleton of the system. The assumption that the amount of time a user spends on page correlates to whether the page should be classified as a navigation or content page for that user. The other criterion, the identity information, is another important point of the thesis. In case of having no recommendation according to the past experiences of the visitor, the identity information is located into appropriate parent domain or class to get other recommendation according to the interests of the visitors coming from its parent domain or class because we assume that the visitors from the same domain will have similar interests. Besides, the system is designed in such a way that it uses the resources of the system efficiently. "Memory Management", "Disk Capacity" and "Time Factor" options have been used in our system in the scope of "Efficient Use of the Resources" concept. We have tested the system on the web site of CS Department of Bilkent University. The results of the experiments have shown the efficiency and applicability of the system.

Keywords: Access log file, personalization, identity information, recommendation.

BU-CE-0208: PDF

Benefit Maximizing Classification Using Feature Intervals (M. Sc. Thesis)

Nazlı Ikizler

For a long time, classification algorithms have focused on minimizing the quantity of prediction errors by assuming that each possible error has identical consequences. However, in many real-world situations, this assumption is not convenient. For instance, in a medical diagnosis domain, misdiagnosing a sick patient as healthy is much more serious than its opposite. For this reason, there is a great need for new classification methods that can handle asymmetric cost and benefit constraints of classifications. In this thesis, we discuss cost-sensitive classification concepts and propose a new classification algorithm called Benefit Maximization with Feature Intervals (BMFI) that uses the feature projection based knowledge representation. In the framework of BMFI, we introduce five different voting methods that are shown to be effective over different domains. A number of generalization and pruning methodologies based on benefits of classification are implemented and experimented. Empirical evaluation of the methods has shown that BMFI exhibits promising performance results compared to recent wrapper cost-sensitive algorithms, despite the fact that classifier performance is highly dependent on the benefit constraints and class distributions in the domain. In order to evaluate cost-sensitive classification techniques, we describe a new metric, namely benefit accuracy which computes the relative accuracy of the total benefit obtained with respect to the maximum possible benefit achievable in the domain.

Keywords: machine learning, classification, cost-sensitivity, benefit maximization, feature intervals, voting, pruning.

BU-CE-0209: PDF

KiMPA: A Kinematics-Based Method for Polygon Approximation

Ediz Şaykol, Gürcan Güleşir, Uğur Güdükbay, Özgür Ulusoy

In different types of information systems, such as multimedia information systems and geographic information systems, object-based information is represented via polygons corresponding to the boundaries of object regions. In many applications, the polygons have large number of vertices and edges, thus a way of representing the polygons with less number of vertices and edges is developed. This approach, called polygon approximation, or polygon simplification, is basically motivated with the difficulties faced in processing polygons with large number of vertices. Besides, large memory usage and disk requirements, and the possibility of having relatively more noise can also be considered as the reasons for polygon simplification. In this paper, a kinematics-based method for polygon approximation is proposed. The vertices of polygons are simplified according to the velocities and accelerations of the vertices with respect to the centroid of the polygon. Another property of the proposed method is that the user may set the number of vertices to be in the approximated polygon, and may hierarchically simplify the output. The approximation method is demonstrated through the experiments based on a set of polygonal objects.

BU-CE-0210: PDF

Rule-Based Spatio-Temporal Query Processing for Video Databases

Mehmet Emin Dönderler, Özgür Ulusoy and Uğur Güdükbay

In our earlier work, we proposed a novel architecture for a Web-based video database management system providing an integrated support for both spatio-temporal and semantic video queries. In this paper, we focus on the task of query processing for spatio-temporal queries, which may contain any combination of directional, topological, 3D-relation, external-predicate, object-appearance, trajectory-projection, and similarity-based object-trajectory conditions. We also propose an SQL-like textual video query language that has the capability to handle a broad range of spatio-temporal queries. The query language is rule-based in that it allows users to express the spatial query conditions on video data in terms of Prolog-type predicates. In our video database management system, called BilVideo (Bilkent Video), spatio-temporal query processing is carried out in five main stages: lexical analysis (lexer), syntax checking and parse-tree production (parser), query decomposition and query-tree construction, subquery and interval processing, and final query result formation.

Keywords: Spatio-temporal relations, spatio-temporal query processing, content-based retrieval, knowledge representation, inference rules, video databases, multimedia databases.

BU-CE-0211: PDF

Data Modeling and Querying for Video Databases (Ph. D. Thesis)

Mehmet Emin Dönderler

With the advances in information technology, the amount of multimedia data captured, produced and stored is increasing rapidly. As a consequence, multimedia content is widely used for many applications in today's world, and hence, a need for organizing this data and accessing it from repositories with vast amount of information has been a driving stimulus both commercially and academically. In compliance with this inevitable trend, first image and especially later video database management systems have attracted a great deal of attention since traditional database systems are not suitable to be used for multimedia data. In this thesis, a novel architecture for a video database system is proposed. The architecture is original in that it provides full support for spatio-temporal queries that contain any combination of spatial, temporal, object-appearance, external-predicate, trajectory-projection and similarity-based object-trajectory conditions by a rule-based system built on a knowledge-base, while utilizing an object-relational database to respond to semantic (keyword, event/activity and category-based) and low-level (color, shape and texture) video queries. Research results obtained from this thesis work have been realized by a prototype video database management system, which we call BilVideo. Its tools, Fact-Extractor and Video-Annotator, its Web-based visual query interface and its SQL-like textual query language are presented. Moreover, the query processor of BilVideo and our spatio-temporal query processing strategy are also discussed.

Keywords: Video databases, multimedia databases, information systems, video data modeling, content-based retrieval, spatio-temporal relations, spatio-temporal query processing, video query languages.

BU-CE-0212: PDF

A Content-Based Image Retrieval System for Texture and Color Queries (M. Sc. Thesis)

Eyüp Sabri Konak

In recent years, very large collections of images and videos have grown rapidly. In parallel with this growth, content-based retrieval and querying the indexed collections are required to access visual information. Two of the main components of the visual information are texture and color. In this thesis, a content-based image retrieval system is presented that computes texture and color similarity among images. The underlying technique is based on the adaptation of a statistical approach to texture analysis. An optimal set of five second-order texture statistics are extracted from the Spatial Grey Level Dependency Matrix of each image, so as to render the feature vector for each image maximally informative, and yet to obtain a low vector dimensionality for efficiency in computation. The method for color analysis is the color histograms, and the information captured within histograms is extracted after a pre-processing phase that performs color transformation, quantization, and filtering. The features thus extracted and stored within feature vectors are later compared with an intersection-based method. The system is also extended for pre-processing images to segment regions with different textural quality, rather than operating globally over the whole image. The system also includes a framework for object-based color and texture querying, which might be useful for reducing the similarity error while comparing rectangular regions as objects. It is shown through experimental results and precision-recall analysis that the content-based retrieval system is effective in terms of retrieval and scalability.

Keywords: Texture Analysis, Color Histograms, Texture Similarity Measurement, Content-Based Image Retrieval, Image Databases.

BU-CE-0213: PDF

An Efficient Query Optimization Strategy for Spatio-Temporal Queries in Video Databases (M. Sc. Thesis)

Gülay Ünel

The interest for multimedia database management systems has grown rapidly due to the need for the storage of huge volumes of multimedia data in computer systems. An important building block of a multimedia database system is the query processor, and a query optimizer embedded to the query processor is needed to answer user queries efficiently. Query optimization problem has been widely studied for conventional database systems, however it is a new research area for multimedia database systems. Due to the differences in query processing strategies, query optimization techniques used in multimedia database systems are different from those used in traditional databases. In this paper, a query optimization strategy is proposed for processing spatio-temporal queries in video database systems. The proposed strategy includes reordering algorithms to be applied on query execution tree. The performance results obtained by testing the reordering algorithms on different query sets are also presented.

Keywords: Video databases, query optimization, query tree, querying of video data.

BU-CE-0214: PDF

A Semantic Data Model and Query Language for Video Data (M. Sc. Thesis)

Umut Arslan

Advances in compression techniques, decreasing cost of storage, and high-speed transmission have facilitated the way video is created, stored and distributed. As a consequence, video is now being used in many application areas. The increase in the amount of video data deployed and used in today's applications not only caused video to draw more attention as a multimedia data type, but also led to the requirement of efficient management of video data. Management of video data paved the way for new research areas, such as indexing and retrieval of videos with respect to their spatio-temporal, visual and semantic contents. In this thesis, semantic content of video is studied, where video metadata, activities, actions and objects of interest are considered within the context of video semantic content. A data model is proposed to model video semantic content, which is extracted from video data by a video annotation tool. A video query language is also provided to support semantic queries on video data.

The outcome of this thesis work will be used in a project, which proposes a video database system architecture with spatio-temporal, object-trajectory and object-apperance query facilities so as to build a complete video search system to query video data by its spatio-temporal, visual and semantic features.

Keywords: Video databases, semantic video modeling, annotation of video data, semantic querying of video data

BU-CE-0215: PDF

Modeling and Animating Personalized Faces (M. Sc. Thesis)

Fatih Erol

A very important and challenging problem in computer graphics is modeling and animation of individualized face models. In this thesis, we describe a facial modeling and animation system attempting to address this problem. The system uses muscle-based generic face model and deforms it using deformation techniques to model individualized faces. Two orthogonal photos of the real faces are used for this purpose. Image processing techniques are employed to extract certain features on the photographs, which are then refined manually by the user through the facilities of the user interface of the system. The feature points located on the frontal and side views of a real face are used to deform the generic model. Then, the muscle vectors in the individualized face model are arranged accordingly. Individualized face models produced in this manner are animated using parametric interpolation techniques.

Keywords: Facial animation, rendering, texture mapping, deformation, feature extraction.

BU-CE-0216: PDF

Simplification of Tetrahedral Meshes by Scalar Value Assignment (M. Sc. Thesis)

Emre Can Sezer

A new approach to simplification of volumetric data over an unstructured tetrahedral mesh is presented. The data consist of sample values of a scalar field defined over a spatial domain, which is subdivided with a tetrahedral mesh. Simplification is performed by means of contraction of the tetrahedra and also of the edges. The simplification algorithm can provide a continuum of aproximate models of the given dataset with any desired degree of accuracy. Hence, the simplification method is suitable for multi-resolution modeling.

The novelty of the approach comes from the arbitrariness in the selection of the point to which a tetrahedron or an edge is contracted. Unlike most of the existing methods, the final vertex of the contraction need not be a vertex of the original mesh. The scalar value to be assigned to the final vertex of contraction is determined by an extremely simple method (both conceptually and computationally), which also provides an estimate of the error of simplification.

The proposed method is applied to two volumetric grids to illustrate its effectiveness in simplification of volumetric data.

Keywords: Volumetric dataset, tetrahedral mesh, tetrahedron contraction, edge contraction, scalar value assignment.

BU-CE-0217: PDF

Comparison of Four Approximating Subdivision Surface Schemes (M. Sc. Thesis)

Tekin Kabasakal

The idea of subdivision surfaces was first introduced in 1978, and there are many methods proposed till now. A subdivision surface is defined as the limit of repeated recursive refinements. In this thesis, we studied the properties of approximating subdivision surface schemes. We started by modeling a complex surface with splines that typically requires a number of spline patches, which must be smoothly joined, making splines burdensome to use. Unlike traditional spline surfaces, subdivision surfaces are defined algorithmically. Subdivision schemes generalize splines to domains of arbitrary topology. Thus, subdivision functions can be used to model complex surfaces without the need to deal with patches. We studied four well-known schemes Catmull-Clark, Doo-Sabin, Loop and the sqrt(3)-subdivision. The first two of these schemes are quadrilateral and the other two are triangular surface subdivision schemes. Modeling sharp features, such as creases, corners or darts, using subdivision schemes requires some modifications in subdivision procedures and sometimes special tagging in the mesh. We developed the rules of sqrt(3)-subdivision to model such features and compared the results with the extended Loop scheme. We have implemented exact normals of Loop and p3-subdivision since using interpolated normals causes creases and other sharp features to appear smooth.

Keywords: Computational geometry and object modeling, subdivision surfaces, Loop, Catmull-Clark, Doo-Sabin, sqrt(3)-subdivision, modeling sharp features.

BU-CE-0218: PDF

On-Line New Event Detection and Event Clustering Using the Concepts of the Cover Coefficient Based Clustering Methodology (M. Sc. Thesis)

Ahmet Vural

In this study, we use the concepts of the cover coefficient-based clustering methodology (C3M) for on-line new event detection and event clustering. The main idea of the study is to use the seed selection process of the C3M algorithm for the purpose of detecting new events. Since C3M works in a retrospective manner, we modify the algorithm to work in an on-line environment. Furthermore, in order to prevent producing oversized event clusters, and to give equal chance to all documents to be the seed of a new event, we employ the window size concept. Since we desire to control the number of seed documents, we introduce a threshold concept to the event clustering algorithm. We also use the threshold concept, with a little modification, in the on-line event detection. In the experiments we use TDT1 corpus, which is also used in the original topic detection and tracking study. In event clustering, we use both binary and weighted versions of TDT1 corpus. With the binary implementation, we obtain better results. When we compare our on-line event detection results to the results of UMASS approach, we obtain better performance in terms of false alarm rates.

Keywords: Clustering, on-line event clustering, on-line event detection.