The present invention provides a method, apparatus and computer program product for combining a plurality of run units into a single executable file. According the invention each run unit may contain one or more data entities which are designated as being required only once in an executable file. As a result when the executable file is built, if a run unit with a data entity of a given value is to be added to an executable file, if a previous run unit with a data entity with a matching value has previously been added to the executable file, the run unit is added to the executable file but without the data entity.