As a first step toward standardization of a practical programming language for fuzzy system applications, we proposed Fuzzy system Description Language (FDL) in 1996. The specification of the first version of FDL was not definitive edition. This specification was designed for hardware-coding of fuzzy control systems based on fuzzy inference as a prerequisite. So although it fulfills the intended functions, several problems arise for unexpected applications.
In this article, we first describe the specification of standardized FDL with its background and properties. Then, we consider some problems (the assignment operation, the comparison operation and the internal expressions, etc.) arised from wide applications of FDL. We describe the improvements of FDL. At last, we describe the fuzzy inference systems based on the indirect inference method with FDL and discuss some properties.