Computer systems in which the knowledge of experts can be incorporated into the system (hence they are also known (loosely) as knowledge-based systems). An expert system has two parts – a knowledge base, and an inference engine which works on the knowledge base. Such systems are particularly useful for dealing with highly complex tasks (e.g., network management, medical diagnosis) in which it is difficult to make the expertise of specialists sufficiently explicit to incorporate in a conventional computer program. IBM forays into expert systems have included CSF DEDALE, Epistle, ESCE/PC, ESE, Handy, KnowledgeTool, KEE, TQA, YES/MVS, TIRS, Integrated Reasoning Shell, GPSI, Neural Network Utility. Unfortunately, expert systems never really delivered on their promise, and their failure gave Artificial Intelligence (AI) a black eye in the business world. AI has been quietly used in many successful software products in the last few years, now that the processing power exists to actually make it work properly.