The paper discusses the problem of building a unified system for a metallurgical enterprise that integrates heterogeneous information systems of various purposes, such as Computerized Information Systems (CIS), Manufacturing Execution Systems (MES), Enterprise Resource Planning (ERP), and Process Automation Systems (PAS). Data exchange with various automated systems of the enterprise is carried out by a special Data Exchange Module with Automated Systems of the Enterprise (DEMAS), which is implemented as a web service. DEMAS aims to ensure guaranteed information exchange between information systems and store information in a single data repository.