Search Engines are now relying on the science of Information Retrieval (IR) and the two critical components for the functionality. First, is relevance in which the degree of the documents is being returned by search engine, depending on the purpose and terms that matched the user’s query. Second, the popularity when relative importance is being measured by citation of a given document that matches the terms or phrase of the user’s.
The two critical components have been translated to web search in the form of document analysis and link analysis. In document analysis, SE looks at in the form of Essential HTML; Meta Tags, heading, Alt text, body, and the quality itself. While, in link analysis is not only measure the quality of link but also consider what they say about that page or site.