An accessible implementation of MAC for file access is proposed. Instead of traditional but unfamiliar MAC aware tools such as secure-OSs, the security enforcement mechanism of our proposal is FSG (file server group) which is structured so that they reflect a security policy of the organization. Using ordinal file servers, it is accessible to the most of commercial office environment. We also propose the use of FCA (formal concept analysis), a technology for knowledge extraction, to derive the structure of FSG for information flow enforcement. An advantage of use of FCA is that it directly produces configuration parameters such as access points of users as the knowledge extracted from organizational security policy. The configuration of the file server group is easy to understand, and the management cost of FSG is lower than that of the ordinary flat structured file servers.