Implementation Of XQuery, A XML Query Language

As a markup language, XML(eXtensible Markup Language) will be the next internet standard of information exchanging for its capability of representing various kind of data and interoperability through heterogenous applications. Combined with database techniques, there comes forth the concept of XML database. Researches on XML database theory and techniques are becoming more hot. In this filed, XML query language constitutes one of the most important facets of XML data processing.On October ,2001, the W3C(World Wide Web Consortium)proposed a working draft specification on XML query language-XQuery. XQuery is a descriptive language which can query any XML-structured data, physically store in medium or viewed as XML. As a developing language, its hierarchy and features were studied. Based on the research of XQuery, we implement the XQuery process engine using Java.We will compare some other query language implements' technique based on our research, then we will illustrate the structure of our implement query engine. Directed by this structure, we define 4 main procedures in XQuery processing: lexical/grammar analysis, conversion between two grammars, typing and evaluation. In this paper, all these steps are covered.Particularly, instead of using in-memory tree nodes and pointers, we use XML to store and represent all data in our processing engine. As the medium of data exchanging, we will show that using XML gives the foundation of distribute process.XQuery is strongly typed descriptive language, its typing system will be one of the focus we make. We will give the most important two relationships' algorithms : subtype and inDOM.At the end of this paper, we will give the performance analyzing and optimizing strategies. Further works and developments will also be given.In particular, we make four contributions mainly:1. A XQuery process engine is proposed and we implement it. Based on this engine, which is the core of XML database, there can be much relative theoretic researches and applications.2. Using XML as the main data structure of XQuery process. This reduces lots of complexities of implements and give the bases of distributive processing.3. Two TA-based algorithms : subtype and inDOM are developed to supply the typing system.4. Evaluation of performance and optimize strategy are given for further develop.