1. An access control system for mediating access to an electronic resource comprising: an object entity having the following attributes: an integrity level attribute, and a write control attribute; a subject entity having the following attributes: a read attribute, and a write attribute; an access mediation rules system that implements the following rules with respect to said object entity and said subject entity: a first rule whereby writing by said subject entity into said object entity is inhibited if the write attribute of said subject entity is lower than said write control attribute of said object entity; a second rule whereby reading by said subject entity of said object entity is inhibited if the read attribute of said subject entity is lower than said integrity level attribute of said object entity.