Spatial Metadata are used to describe the existing data sources in order to facilitate their access and sharing between different actors. The problem of exploitation of these metadata arises when they should be catalogued within the framework of a platform for spatial data federation. We describe a service oriented approach for structuring this component, with an implementation based on LDAP. To achieve this, we start from a canonical language that unifies the major known geographic metadata standards, and then we define new classes of LDAP objects which map syntactic units of canonical language.