ABSTRACT It has become highly desirable to provide users with flexible ways to query/search information over databases as simple as keyword search like Google search. This book surveys the recent developments on keyword search over databases, and focuses on finding structural information among objects in a database using a set of keywords. Such structural information to be returned can be either trees or subgraphs representing how the objects, that contain the required keywords, are interconnected in a relational database or in an XML database. The structural keyword search is completely different from finding documents that contain all the user-given keywords.The former focuses on the interconnected object structures, whereas the latter focuses on the object content. The book is organized as follows. In Chapter 1, we highlight the main research issues on the structural keyword search in different contexts. In Chapter 2, we focus on supporting structural keyword search in a relational database management system using the SQL query language. We concentrate on how to generate a set of SQL queries that can find all the structural information among records in a relational database completely, and how to evaluate the generated set of SQL queries efficiently.In Chapter3,wediscussgraph algorithms forstructural keywordsearch by treating an entire relational database as a large data graph. In Chapter 4,we discuss structural keyword search in alarge tree-structured XML database.In Chapter5,we highlight several interesting research issues regarding keyword search on databases. The book can be used as either an extended survey for people who are interested in the structural keyword search or a reference book for a postgraduate course on the related topics. KEYWORDS keyword search, interconnected object structures, relational databases, XML databases, data stream, rank To my wife, Hannah my children, Michael and Stephen Jeffrey Xu Yu To my wife, Michelle my parents, Hanmin and Yaping Lu Qin To my parents, Qiyuan and Yumei Lijun Chang ix Contents Preface xi 1 Introduction 1 2 Schema-Based Keyword Search on Relational Databases 3 2.1 Introduction 3 2.2 Candidate Network Generation 12 2.3 Candidate Network Evaluation 21 2.3.1 Getting All MTJNT s in a Relational Database 22 2.3.2 Getting Top-k MTJNT s in a Relational Database 29 2.4 Other Keyword Search Semantics 34 3 Graph-Based Keyword Search 45 3.1 Graph Model and Problem Definition 45 3.2 Polynomial Delay and Dijkstra’s Algorithm 49 3.3 Steiner Tree-Based Keyword Search 53 3.3.1 Backward Search 53 3.3.2 Dynamic Programming 55 3.3.3 Enumerating Q-subtrees with Polynomial Delay 57 3.4 Distinct Root-Based Keyword Search 69 3.4.1 Bidirectional Search 69 3.4.2 Bi-Level Indexing 71 3.4.3 External Memory Data Graph 73 3.5 Subgraph-Based Keyword Search 76 3.5.1 r-Radius Steiner Graph 76 3.5.2 Multi-Center Induced Graph 78 x CONTENTS 4 Keyword Search in XML Databases 83 4.1 XML and Problem Definition 83 4.1.1 LCA, SLCA, ELCA, and CLCA 84 4.1.2 Problem Definition and Notations 87 4.2 SLCA-Based Semantics 88 4.2.1 Properties of LCA and SLCA 89 4.2.2 Efficient Algorithms for SLCAs 90 4.3 Identify Meaningful Return Information 98 4.3.1 XSeek 99 4.3.2 Max Match 102 4.4 ELCA-Based Semantics 106 4.4.1 Efficient Algorithms for ELCAs 107 4.4.2 Identifying Meaningful ELCAs 111 4.5 Other Approaches 112 5 Other Topics for Keyword Search on Databases 115 5.1 Keyword Search Across Databases 115 5.1.1 Selection of Databases 115 5.1.2 Answering Keyword Queries Across Databases 119 5.2 Keyword Search on Spatial Databases 120 5.2.1 Points as Result 120 5.2.2 Area as Result 121 5.3 Variations of Keyword Search on Databases 123 5.3.1 Objects as Results 123 5.3.2 Subspaces as Results 125 5.3.3 Terms as Results 126 5.3.4 sql Queries as Results 128 5.3.5 Small Database as Result 129 5.3.6 Other Related Issues 130 Bibliography 133 Authors’ Biographies 143 . required keywords, are interconnected in a relational database or in an XML database. The structural keyword search is completely different from finding documents that contain all the user-given keywords.The. 49 3.3 Steiner Tree-Based Keyword Search 53 3.3.1 Backward Search 53 3.3.2 Dynamic Programming 55 3.3.3 Enumerating Q-subtrees with Polynomial Delay 57 3.4 Distinct Root-Based Keyword Search 69 3.4.1. on the structural keyword search in different contexts. In Chapter 2, we focus on supporting structural keyword search in a relational database management system using the SQL query language.