whole step
4.For the convenience of reader to understand the structure of STEP-NC, thus to know the design of the whole system, we outline the STEP standard and its file structures in chapter 2, and the context of STEP-NC and the relationship between STEP and STEP-NC in chapter 3.In the process of designing Pre-Processor, we emphasize the data source of STEP-NC and the format of describing these data in STEP-NC file.

