The invention proposes a directory server, capable of interacting with entries organized in a tree structure. Each entry has attributes, these attributes comprising real attributes each having a value stored in the entry. The directory server comprising: a mechanism capable of associating a virtual attribute to an entry, subject to a virtual attribute condition being verified, the virtual attribute condition being derived from data located elsewhere in the tree structure, and a resolving function, capable of receiving a first filter expression, based on a virtual attribute, for converting it into one or more second filter expressions, containing real attributes, and being computed from the first filter expression and from the virtual attribute condition.