In this chapter we have described a wide variety of retrieval models and ranking algorithms. From the point of view of someone involved in designing and implementing a search application, the question is which of these techniques should be used and when? The answer depends on the application and the tools available.
Most search applications involve much smaller collections than the Web and a lot less connectivity in terms of links and anchor text. Ranking algorithms that work well in web search engines often do not produce the best rankings in other applications.
Customizing a ranking algorithm for the application will nearly always produce the best results.