A system for selecting a candidate information unit for linking to a given information unit based on the content of the given information unit. The content of the given information unit may be automatically determined and then compared to content of the candidate information unit to determine which unit of candidate information to select. When the unit of candidate information is selected, it bears a chosen given information unit and it is linked with the given information unit. The system can be used to implement a structured advertising system for the World Wide Web. Web pages (given information) are searched and indexed, producing indexed content data. This indexed content data is then ranked according to relevancy. The ranked content data are compared to content data of advertisements (candidate information) and an advertisement is selected. The advertisement is then copied onto (linked to) the Web page.