The work presented in this thesis is related to XML which is a dominant standard on the Web used to encode data. In order to retrieve data from the Web, query languages are needed. A well known standard for querying XML data is the language XQuery where data retrieval is based on path navigation. A different approach using pattern matching instead of path navigation is developed in the declarative rule-based query language Xcerpt,which is inspired by logic programming. Further development of Xcerpt is one of the objectives of the Network of Excellence REWERSE1. This thesis is a contribution to this effort.
Contents
1 Introduction
2 Background
2.1 Introduction to Xcerpt
2.1.1 Language Overview
2.1.2 Formal Semantics
2.2 XML Schema Languages
2.2.1 DTD
2.2.2 XML Schema
2.2.3 Relax NG
2.3 XQuery and its Type System
2.3.1 Data Model
2.3.2 Language Constructs
2.3.3 Type System
2.4 DIG Interface
3 Type Specification
3.1 Type Definitions
3.1.1 Proper Type Definitions
3.2 Operations on Types
3.2.1 Emptiness Check
3.2.2 Intersection of Types
3.2.3 Type Inclusion
3.3 Type Definitions and XML Schema Languages
3.3.1 DTD
3.3.2 XML Schema
3.3.3 Relax NG
4 Reasoning about Types
4.1 Motivation
4.2 Type Inference for Xcerpt
4.2.1 Variable-type Mappings
4.2.2 Typing of Query Rules
4.2.3 Typing of Progra
4.2.4 Exactness of Type Inference
4.2.5 Type Inference Algorithm for Query Rules
4.2.6 Typing of Remaining Xcerpt Constructs
4.3 Type-based Rule Dependency
4.4 Discovering of Type Errors
4.5 Relation to XQuery Type System
5 Type System Prototype
5.1 Usage of the Prototype
5.2 Overall Structure of the Source Code
6 Use Cases
6.1 CD Store
6.2 Bibliography
6.2.1 No Result Type Specified
6.2.2 Result Type Specified
6.3 Bookstore
6.4 Clique of Friends
7 Semantic Types
7.1 Ontology Classes in Type Definitions
7.2 DigXcerpt: Ontology Queries in Xcerpt
7.2.1 Syntax and Semantics
7.2.2 Implementation
7.2.3 Discussion
8 Conclusions
A Proofs
A.1 Type System Correctness
A.1.1 Type Inference for Rules
A.1.2 Type Inference for Programs
A.2 Exactness of Inferred Type
A.3 Soundness of DigXcerpt Implementation
B Typechecker Results
Bibliography
Author: Wilk, Artur
Source: Linköping University
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