Laurent Mignet

The XML web: a first study

Although originally designed for large-scale electronic publishing, XML plays an increasingly important role in the exchange of data on the Web. In fact, it is expected that XML will become the lingua franca of the Web, eventually replacing HTML. Not surprisingly, there has been a great deal of interest on XML both in industry and in academia. Nevertheless, to date no comprehensive study on the XML Web (i.e., the subset of the Web made of XML documents only) nor on its contents has been made. This paper is the first attempt at describing the XML Web and the documents contained in it. Our results are drawn from a sample of a repository of the publicly available XML documents on the Web, consisting of about 200,000 documents. Our results show that, despite its short history, XML already permeates the Web, both in terms of generic domains and geographically. Also, our results about the contents of the XML Web provide valuable input for the design of algorithms, tools and systems that use XML in one form or another.

Studying the XML Web: Gathering Statistics from an XML Sample

XML has emerged as the language for exchanging data on the web and has attracted considerable interest both in industry and in academia. Nevertheless, to date, little is known about the XML documents published on the web. This paper presents a comprehensive analysis of a sample of about 200,000 XML documents on the web, and is the first study of its kind. We study the distribution of XML documents across the web in several ways; moreover, we provided a detailed characterization of the structure of real XML documents. Our results provide valuable input to the design of algorithms, tools and systems that use XML in one form or another.

Efficient incremental validation of XML documents

We discuss incremental validation of XML documents with respect to DTDs and XML schema definitions. We consider insertions and deletions of subtrees, as opposed to leaf nodes only, and we also consider the validation of ID and IDREF attributes. For arbitrary schemas, we give a worst-case n log n time and linear space algorithm, and show that it often is far superior to revalidation from scratch. We present two classes of schemas, which capture most real-life DTDs, and show that they admit a logarithmic time incremental validation algorithm that, in many cases, requires only constant auxiliary space. We then discuss an implementation of these algorithms that is independent of, and can be customized for different storage mechanisms for XML. Finally, we present extensive experimental results showing that our approach is highly efficient and scalable.

Goals and benchmarks for autonomic configuration recommenders

We are witnessing an explosive increase in the complexity of the information systems we rely upon, Autonomic systems address this challenge by continuously configuring and tuning themselves. Recently, a number of autonomic features have been incorporated into commercial RDBMS; tools for recommending database configurations (i.e., indexes, materialized views, partitions) for a given workload are prominent examples of this promising trend.In this paper, we introduce a flexible characterization of the performance goals of configuration recommenders and develop an experimental evaluation approach to benchmark the effectiveness of these autonomic tools. We focus on exploratory queries and present extensive experimental results using both real and synthetic data that demonstrate the validity of the approach introduced. Our results identify a specific index configuration based on single-column indexes as a very useful baseline for comparisons in the exploratory setting. Furthermore, the experimental results demonstrate the unfulfilled potential for achieving improvements of several orders of magnitude.

Xyleme, a dynamic warehouse for XML data of the Web

The current development of the Web and the generalization of XML technology provide a major opportunity which can radically change the face of the Web. Xyleme intends to be a leader of this revolution by providing database services over the XML data of the Web. Originally, Xyleme was a research project functioning as an open, loosely coupled network of researchers. At the end of 2000, a prototype had been implemented. A start-up company, also called Xyleme, is now turning into a product. The authors summarize the main research efforts of the Xyleme team. They concern: a scalable architecture; the efficient storage of huge quantities of XML data (hundreds of millions of pages); XML query processing with full-text and structural indexing; data acquisition strategies to build the repository and keep it up-to-date; change control with services such as query subscription; and semantic data integration to free users from having to deal with many specific DTDs when expressing queries.

Improving DB2 performance expert – a generic analysis framework

The complexity of software has been dramatically increasing over the years. Database management systems have not escaped this complexity. On the contrary, this problem is aggravated in database systems because they try to integrate multiple paradigms (object, relational, XML) in one box and are supposed to perform well in every scenario unlike OLAP or OLTP. As a result, it is very difficult to fine tune the performance of a DBMS. Hence, there is a need for a external tool which can monitor and fine tune the DBMS. In this extended abstract, we describe a few techniques to improve DB2 Performance Expert, which helps in monitoring DB2. Specifically, we describe a component which is capable of doing early performance problem detection by analyzing the sensor values over a long period of time. We also showcase a trends plotter and workload characterizer which allows a DBA to have a better understanding of the resource usages. A prototype of these tools has been demonstrated to a few select customers and based on their feedback this paper outlines the various issues that still need to be addressed in the next versions of the tool.