This research proposes to modernize a legacy software system by using web services as the main building blocks of the software reengineering. For this purpose, a legacy theorem proof checking and derivation tool called Bertie3 is reengineered in terms of service-oriented architecture, service-oriented componentization, and external data representation and serialization. With the web services of derivation checking engines and first-order markup languages, a minimal amount of development time can be spent working on well-known and well-developed components. More time can be spent updating the features that make the tool unique. This case study shows that modernizing a software system with web services will allow the business components of the system to be easily expanded and integrated with other application components for future demands.