A Web service is a software functionality accessible through the network. Web services are intended to be composed into coarser-grained applications. Achieving a required composite functionality requires the discovery of a collection of Web services out of the enormous service space. Each service must be examined to verify its provided functionality, making the selection task neither efficient nor practical. Moreover, when a service in a composition becomes unavailable, the whole composition may become functionally broken. Therefore, an equivalent service must be retrieved to replace the broken one, thus spending more time and effort. In this paper, we propose an approach for Web service classification based on FCA, using their operations estimated similarities. The generated lattices make the identification of candidate substitutes to a given service straightforward. Thus, service compositions can be achieved more easily and with backup services, so as to easily recover the functionality of a broken service.