Detailed herein is a technology which, among other things, allows a search engine to utilize a user-defined relevance function. In one approach to the technology, a method of applying a user-defined relevance function is described. In this approach, a complex search query is decomposed into a simple operator. The simple operator is associated with the user-defined relevance function. A document which matches the search query is retrieved, and a rank is calculated for the document, using the user-defined relevance function.