Web services are becoming a significant part of Web applications in different fields such as e-commerce applications. A problem that is facing Web services is that the Web services datatype descriptions inside Web Services Description Language are difficult to be understood by service providers or requesters due to many reasons; one of these reasons is the lack of expressiveness of the Schema based datatype system that is used to describe provider side datatypes inside Web Services Description Language. This problem leads to producing vague, custom and inconsistent datatype descriptions by different Web services development techniques inside the auto-generated Web Services Description Languages. This paper proposes an approach to formally model Web services datatype descriptions in order to solve the previous problem. The approach is based on mapping the datatype section inside a Web Services Description Language into a more understandable tree and models. Following the paper’s approach, service requesters can understand the datatype descriptions of the provided operations by a Web service inside Web Services Description Language and consequently this will make it easier to invoke these operations. A prototype tool has been built and it proved to be efficient in enhancing Web services understandability.