Challenges in Web Search Engines

This article presents a high-level discussion of some problems that are unique to web search engines. The goal is to raise awareness and stimulate research in these areas. Web search engines are faced with a number of difficult problems in maintaining or enhancing the quality of their performance. These problems are either unique to this domain, or novel variants of problems that have been studied in the literature. Our goal in writing this article is to raise awareness of several problems that we believe could benefit from increased study by the research community. We deliberately ignore interesting and difficult problems that are already the subject of active research.