of pages which we consider to be good sources of links on specific topics, albeit unknown. This is done as follows: Considering all pages with out-degree greater than a threshold, k (e.g., k=5) we test to see if these URLs point to k distinct non-affiliated hosts. Every such page is considered an expert page. If a broad classification (such as Arts , Science , Sports etc.) is known for every page in the search engine database then we can additionally require that most of the k non-affiliated URLs discovered in the previous step point to pages that share the same broad classification. This allows us to distinguish between random collections of links and resource directories. Other properties of the page such as regularity in formatting can be used as well. 2.3 Indexing the Experts To locate expert pages that match user queries we create an inverted index to map keywords to experts on which they occur. In doing so we only index text contained within "key phrases" of the expert. A key phrase is a piece of text that qualifies one or more URLs in the page. Every key phrase has a scope within the document text. URLs located within the scope of a phrase are said to be "qualified" by it. For example, the title, headings (e.g., text within a pair of &lt;H1&gt; &lt;/H1&gt; tags) and anchor text within the expert page are considered key phrases. The title has a scope that qualifies all URLs in the document. A