A maintenance system for an offshore plant uses an optimal maintenance method, process, and period based on operation information data and economic evaluation techniques. Maintenance is performed after one or more indicators show that equipment is going to fail or that equipment performance is deteriorating. A maintenance system is based on the use of real-time data to prioritize and optimize the LNG-FPSO topside equipment resources. In this paper, a maintenance system is designed for LNG-FPSO topside equipment based on the IDEF0 and UML methodologies. First, the system is designed from the user requirements. Then, a standardized development environment and tools are selected. These tools are used to define and evaluate the core application technologies for the system development.