Software engineering involves techniques for the design, testing and evaluation of software systems, focusing on reliability attributes. Design is a meaningful engineering representation of something that has to be built. It can be traced to a customer's requirements and at the same time assessed for quality against a set of predefined criteria for 'good' design. Design for reliability is achieved by fault-tolerance techniques that keep the system working in the presence of software faults. Testing for reliability is achieved by fault-removal techniques that detect and correct software faults before the system is deployed. Evaluation for reliability is achieved by fault-prediction techniques that model and measure the reliability of the system during its operation. In the software engineering context, design focuses on four major areas of concern, data, architecture, interfaces, and components.