WebCrawler: Finding what people want.

摘要

WebCrawler, the first comprehensive full-text search engine for the World-Wide Web, has played a fundamental role in making the Web easier to use for millions of people. Its invention and subsequent evolution, spanning a three-year period, helped fuel the Web's growth by creating a new way of navigating hypertext.; Before search engines like WebCrawler, users found Web documents by following hypertext links from one document to another. When the Web was small and its documents shared the same fundamental purpose, users could find documents with relative ease. However, the Web quickly grew to millions of pages making navigation difficult. WebCrawler assists users in their Web navigation by automating the task of link traversal, creating a searchable index of the web, and fulfilling searchers' queries from the index. To use WebCrawler, a user issues a query to a pre-computed index, quickly retrieving a list of documents that match the query.; This dissertation describes WebCrawler's scientific contributions: a method for choosing a subset of the Web to index; an approach to creating a search service that is easy to use; a new way to rank search results that can generate highly effective results for both naive and expert searchers; and an architecture for the service that has effectively handled a three-order-of-magnitude increase in load.; This dissertation also describes how WebCrawler evolved to accommodate the extraordinary growth of the Web. This growth affected WebCrawler not only by increasing the size and scope of its index, but also by increasing the demand for its service. Each of WebCrawler's components had to change to accommodate this growth: the crawler had to download more documents, the full-text index had to become more efficient at storing and finding those documents, and the service had to accommodate heavier demand. Such changes were not only related to scale, however: the evolving nature of the Web meant that functional changes were necessary, too, such as the ability to handle naive queries from searchers.