Vertical search engines focus on specific slices of content, such as the Web
of a single country or the document collection of a large corporation. Despite
this, like general open web search engines, they are expensive to maintain,
expensive to operate, and hard to design. Because of this, predicting the
response time of a vertical search engine is usually done empirically through
experimentation, requiring a costly setup. An alternative is to develop a model
of the search engine for predicting performance. However, this alternative is
of interest only if its predictions are accurate.