In this research, we try to show the major features of prolog which make it a strong expressive language about writing the expert systems and the traditional languages lacks them as Pascal language. We also provide expert system, the purpose of it is the Inventory Control by apply the Fixed-Order Quantity Model, and we clearified concept of the static and dynamic data in Prolog. Finally, we compared between the databases in prolog and some of their quires with Access and SQL. Expert systems are considered as one of the main applications of artificial intelligence, which are known as knowledge based systems. And the expert systems are computer applications which embody some non-algorithmic expertise for solving certain types of problems. For example, the problems which provide advice, analysis, classification, diagnostic, explanation, teaching, or designing…etc.