1. A method of managing access to a pool of computer and network resources made available by a cloud computing system to an entity having a plurality of users, the method comprising: an updating process: of updating a first model describing the pool of computer and network resources; and of updating a second model describing the entity, the second model being hierarchical and having a plurality of levels, each level of the second model having at least one element containing one or more users of the entity, each element of a said hierarchical level being associated with an algorithm for allocating at least a portion of the pool of resources, the union of the elements of a hierarchical level containing all of the users of the entity, wherein at least one algorithm for allocating at least a portion of the pool of resources associated with an element of a hierarchical level of the second model is an algorithm that allocates a fixed portion of the resources to said element, with the resources that are not allocated to said element being shared among the other elements of the hierarchical level; said updating process being performed in such a manner that the first model and the second model represent a current state of the pool of resources and a current state of the entity; on receiving a request from at least one user of the entity to access at least one resource of the pool of resources as specified in the request: an identification process of identifying resources for said at least one user from within the pool of resources, by applying resource allocation algorithms associated with the elements of the second model kept up to date with the current state of the pool of resources represented by the first model; a verification process of verifying compatibility between the resources identified for said at least one user and said at least one resource specified in the request; and a rejection process of rejecting the request in the event of incompatibility.