Information extraction from Web sites is nowadays a relevant problem, usually performed by software modules called wrappers. A key requirement is that the wrapper generation process should be automated to the largest extent, in order to allow for large-scale extraction tasks even in presence of changes in the underlying sites. So far, however, only semi-automatic proposals have appeared in the ...

Wrapper induction techniques traditionally focus on learning wrappers based on examples from one class of Web pages, i.e. from Web pages that are all similar in structure and content. Thereby, traditional wrapper induction targets the understanding of Web pages generated from a database using the same generation template as observed in the example set. Applying such techniques to Web sites gene...

Data extraction from web pages is performed by software modules called wrappers. Recently, some systems for the automatic generation of wrappers have been proposed in the literature. These systems are based on unsupervised inference techniques: taking as input a small set of sample pages, they can produce a common wrapper to extract relevant data. However, due to the automatic nature of the app...

Introduction The Semantic Web is still a vision. The unstructured Web of today contains millions of documents which cannot be queried and where layout and structure are heavily mixed. Moreover, they are not annotated at all. There is a huge gap between Web information and the qualified, structured data as required in corporate information systems. According to the vision of the Semantic Web, al...

To simplify the task of obtaining information from the vast number of information sources that are available on the World Wide Web (WWW), we are building tools to build information mediators for extracting and integrating data from multiple Web sources. In a mediator based approach, wrappers are built around individual information sources, that provide translation between the mediator query lan...

There exist two types of wrappers: the string based wrapper such as the LR wrapper, and the tree based wrapper. A tree based wrapper designates extraction regions by nodes on the trees of semistructured documents. The tree based wrapper seems to be more powerful than the string based one. There exist, however, many HTML documents on the Web such that a standard tree based wrapper fails to extra...

Various web applications in e-business, such as online price comparisons, competition monitoring and personalised newsletters require retrieval of distributed information from the Internet. This paper examines the suitability of software toolkits for the extraction of data from web sites. The term wrapper is defined and an overview of presently available toolkits for generating wrappers is prov...

Literature search and delivery in the World Wide Web becomes a rapidly expanding market. Up to now the search is mostly cost-free. But in the future we expect the appearance of more and more providers charging for their services. The main problems are finding the right provider and extracting the information. UniCats is a system for intelligent information search and extraction from multiple pr...

Web information extraction is a fundamental issue for web information management and integrations. A common approach is to use wrappers to extract data from web pages or documents. However, a critical issue for wrapper development is how to generate extraction rules. In this paper, we propose a novel two-phase rule generation and optimization (2P-RULE) approach for wrapper generation. 2P-RULE c...

The World Wide Web has become one of the most important connections to various sources of information. A large proportion of the data is embedded in HTML documents. This language serves the visual presentation of data in Internet browser, but does not provide semantic information for the data presented. This form of data presentation is, therefore, inappropriate for the demands of automated, co...