WSDIR is a federated directory system which allows registration and discovery of semantic web services. The typical use of this directory system is in a context where ubiquitous business application services should be flexibly coordinated and pervasively provided to the mobile user by intelligent agents in dynamically changing environments. The system has been modeled, designed and implemented as a backbone directory system to be searched by an infrastructure made up by such kind of agents coordinating web services. The system is modeled as a federation: directory services form its atomic units, and the federation emerges from the registration of directory services in other directory services. Directories are virtual clusters of service entries stored in one or more directory services. To create the topology, policies are defined on all possible operations to be called on directories. For instance, they allow for routed registration and selective access to directories. WSDir has been applied as a backbone in the trials of an ehealth emergency application.

UDDI has become the de-facto standard to provide a general framework to describe and discover services and Web service providers. More specifically, WSDL descriptions of web services can be mapped to UDDI data structures, allowing to find web service descriptions using the standard UDDI query interface.
Within the academic world, a number of approaches exist that try to build semantically enhanced discovery components on top of UDDI, augments the standard UDDI registry APIs with semantic annotations, uses a set of distributed UDDI registries as a storage layer, where each registry is mapped to a specific domain based on a registry ontology. This paper presents a new federated directory (or registry) system called WSDir, which allows registration and discovery of OWL-S semantic web services . Our directory system is used in the CASCOM platform where ehealth services should be flexibly coordinated and pervasively provided to the mobile user by intelligent agents in dynamically changing environments.
We modeled, designed and implemented WSDir as a backbone directory system to be searched by an infrastructure made up by such kind of agents coordinating web services. This agent infrastructure therefore is deployed on mobile users: it queries our directory system for OWL-S service descriptions, composes them to achieve a target higher functionality and executes them. WSDir has also been used in the trials of an ehealth emergency application. We followed specific requirements for designing WSDir:

• i) it should have itself a Web service interface to be universally invoked.
• ii) it should be distributed.
• iii) the construction of the network should induce minimal overhead and should be scalable; also, the network should be robust to changes in topology and the number of interactions with the system.
• iv) the directory should allow a great number of services to be registered, and this in a very dynamic way, including lease times.
  

These requirements lead us to model WSDir as a federation: directory services form its atomic units, and the federation emerges from the registration of directory services in other directory services. Directories are virtual clusters of service entries stored in one or more directory services. To create the topology, policies are defined on all possible operations to be called on directories. For instance, they allow for routed registration and selective access to directories.