Abstract: Disclosed are various embodiments for using applications of items in conducting item searches. It is determined, in one or more computing devices, whether a search query string includes an application key. A non-key portion of the search query string that excludes the application key is obtained when the search query string includes the application key. A search is executed on a subset of items in an item catalog using the non-key portion of the search query string to obtain a result set of items. Each item in the subset of items is associated with an item application that matches the application key.

Abstract: Systems, methods, and apparatus are provided for determining relevance of documents to queries. An optimized relevance function is configured to determine a relevance value of documents of a first type that are linked to documents of a second type. The relevance function is optimized to satisfy certain criteria. According to one criterion, a relevance value produced by the optimized relevance function, when invoked for documents of the first type, should have a locally maximal degree of fit to the results of the existing relevance function for the sample training documents of the second type. An assessed degree of fit of a document can be increased or decreased to arrive at an optimized relevance function that ranks the documents of the first type in a desired position relative to documents of the second type in search results. The degree of fit can be assessed by a user-provided objective function.