During search and discovery of Web Services (WS) the user specifies a set of parameters that is compared against the WS operations, this means that one of the main steps in WS discovery is the comparison process. Most of related work aim at improving the WS search process based in the following approaches: semantic description of operations, semantic relation on name functions, workflows, and functions signatures. In this work, a mechanism for evaluating the similarity of WS through comparing the input and output data types of WS operations is presented.