1. A non-transitory, computer-readable recording medium having stored therein a program for causing a computer to execute a process, the process comprising: specifying a relevance between machine part documents which include design information of machine parts, and specifying a keyword of each of the machine part documents; specifying a relevance between electronic part documents which include design information of electronic parts which control the machine parts, and specifying a keyword of each of the electronic part documents; specifying a relevance between program documents which include operations of programs causing the electronic parts to perform a processing, and specifying a keyword of each of the program documents; and associating documents having a common keyword among the specified keywords of the program documents, the electronic part documents, and of the machine part documents so that the program documents, the electronic part documents, and the machine part document are associated with each other, respectively.