A method and apparatus for generating composite documents from document containers using a set of rules to populate slots in the containers with variable content is presented. The present invention allows the user to produce many individual, customized documents from a single container or set of linked containers and a set of content items stored in a database. Each container includes a set of rules that establish one-to-one, one-to-many, many-to-many, or circular mappings between slots and content items. In one or more embodiments, the present invention may be used to create customized composite photograph collages, such as custom school pictures, where each generated document is a photograph collage that features a photograph of an individual student in a central, enlarged, or more prominent position, with smaller photographs of the other students in the class or school in less prominent positions in the collage.