A new expert system can be developed by adding domain knowledge to the shell. The figure depicts generic components of expert system.

Expert System Shell:

Knowledge acquisition system: It is the first and fundamental step. It helps to collect the experts knowledge required to solve the Problems and build the knowledge base.

Knowledge Base: This component is the heart of expert systems. It stores all factual and heuristic knowledge about the application domain. It provides with the various representation techniques for all the data.

Inference mechanism: Inference engine is the brain of the expert system. This component is mainly responsible for generating inference from the given knowledge from the knowledge base and produce line of reasoning in turn the result of the user's query.

Explanation subsystem: This part of shell is responsible for explaining or justifying the final or intermediate result of user query. It is also responsible to justify need of additional knowledge.

User interface: It is the means of communication with the user. It decides the utility of expert system.

Building expert systems by using shells has significant advantages. It is always advisable to use shell to develop expert system as it avoids building the system from scratch.

To build an expert system using system shell, one needs to enter all necessary knowledge about a task domain into the shell.