1. A mediation unit in a telecommunications network for mediating between an application service provider and a plurality of service providers, said unit comprising: recovery means for acquiring user indicators qualifying a user of an application provided by an application server and qualifying a type of data required on that user, the indicators being issued by said application service provider and providing an identification of the user, the recovery means being further for recovering data of said type concerning said user from various service providers; and means for identifying among the various service providers a selection of service providers holding data of said type of data required on the user, the recovery means taking into account said selection of service providers such that only the selected service providers are interrogated; wherein the recovery means include a subscriptions database that contains user indicators identifying users of the application associated with indicators describing types of data required by the application service provider on each user of the application; wherein the means for identifying the selection of service providers is associated with a second database comprising associations between each specific user managed by the means for identifying and service providers having information on said specific user, the selection being obtained from an association in said second database; wherein the recovery means are configured to acquire data from the selected service provider by setting up a notification link between the selected service provider and the recovery means by which the selected service provider provides a notification of data to the recovery means based on an initiative of the selected service provider; and wherein the selected service provider provides a notification of specific data to the recovery means in response to a modification of said specific data.