A selection system and method. The selection method comprises receiving, by a computing system, a taxonomy of data related to a specified domain of knowledge on the web. A taxonomy tree is constructed from the taxonomy. A sub tree related to a sub-domain from specified domain is selected from the taxonomy tree. A first list comprising user expected universal resource locators (URLs) related to the sub-domain is received. A second list comprising topic expressions defining each node of the taxonomy sub-tree is generated. A query based on the second list is generated. The query is applied on an index of URLs generated from a web crawling process to generate a third list. A recall value is calculated based on the first list and the third list.