Data exchange is the problem of finding an instance of a target schema, given an instance of a source schema and a specification of the relationship between the source and the target. Such a target instance should correctly represent information from the source instance under the constraints imposed by the target schema, and it should allow one to evaluate queries on the target instance in a way that is semantically consistent with the source data. Data exchange is an old problem that re-emerged as an active research topic recently, due to the increased need for exchange of data in various formats, often in e-business applications. In this lecture, we give an overview of the basic concepts of data exchange in both relational and XML contexts. We give examples of data exchange problems, and we introduce the main tasks that need to addressed. We then discuss relational data exchange, concentrating on issues such as relational schema mappings, materializing target instances (including canonical solutions and cores), query answering, and query rewriting. After that, we discuss metadata management, i.e., handling schema mappings themselves. We pay particular attention to operations on schema mappings, such as composition and inverse. Finally, we describe both data exchange and metadata management in the context of XML. We use mappings based on transforming tree patterns, and we show that they lead to a host of new problems that did not arise in the relational case, but they need to be addressed for XML. These include consistency issues for mappings and schemas, as well as imposing tighter restrictions on mappings and queries to achieve tractable query answering in data exchange. Table of Contents: Overview / Relational Mappings and Data Exchange / Metadata Management / XML Mappings and Data Exchange
Author(s): Marcelo Arenas, Pablo Barcelo, Leonid Libkin, Filip Murlak
Series: Synthesis Lectures on Data Management
Edition: 1
Publisher: Morgan and Claypool Publishers
Year: 2010
Language: English
Pages: 112
A data exchange example......Page 9
XML data exchange......Page 14
Overview of the main tasks in data exchange......Page 15
Key definitions......Page 16
Bibliographic comments......Page 18
Relational schemas and constraints......Page 19
Relational schema mappings......Page 20
Materializing target instances......Page 22
Existence of Solutions......Page 24
Universal Solutions......Page 25
Materializing Universal Solutions......Page 28
Cores......Page 34
Answering first-order and conjunctive queries......Page 37
Query Rewriting......Page 41
Bibliographical comments......Page 43
Introduction......Page 45
Composition of schema mappings......Page 47
Extending st-tgds with second-order quantification......Page 49
A first definition of inverse......Page 56
Bringing exchanged data back: The recovery of a schema mapping......Page 61
Computing the inverse operator......Page 67
Bibliographic comments......Page 72
XML documents and DTDs......Page 75
Expressing properties of trees......Page 76
XML schema mappings......Page 82
Consistency......Page 85
Absolute consistency......Page 92
Data exchange problem......Page 93
Hardness of query answering......Page 95
Tractable query answering......Page 99
Summary......Page 102
Bibliographic comments......Page 103
Bibliography......Page 105
Authors' Biographies......Page 111
