【正文】 of the implementation of directives. Machinery orders are executable software in the form of the bottom. Hexadecimal or other special code can be used to represent the CPU can lead to specific steps to deal with the binary bit mode. Machine code, assembly language (machinelevel language), and highlevel programming languages are often referred to as the first three generations of puter language. The use of a language, programmers must take into account both the information provided should also consider whether the structure of the control process itself. Therefore, the process of the first three generations of language as language. In the past 10 years, there has been a group of fourth generation language or process language. Nonprocess language requirement does not require software developers details of the process, it is referred to the procedure provides for the appointment rather than the result of the oute of the requirements to achieve its behavior [COB85]. The results show that support software translated into machine executable. So far, the fourthgeneration language (4 GLs) database has been used for other mercial applications and data processing areas. Software applications The software can be applied to the prior provisions of the steps (algorithm) has been defined under any circumstances (this obviously does not meet the rules example is the expert system software). Information content and software applications uncertainty is to determine the nature of the important factors. Content refers to the input and output of the significance of the information and forms. For example, many mercial applications that use highly structured losers were data (databases) and generates formatted statements. Automatic machine control (for example, NC) software to accept a limited form of the structure of discrete and continuous data quickly from the machinegenerated orders. Information certainty that the losers were the timing and sequencing data predictability. Engineering analysis procedures for accepting predefined sequence data, analysis algorithm for implementation, and to give statements or chart form of result data. This application is uncertainty. On the other hand, a multiuser operating system to accept arbitrary changes in the content and timing of transmission, the implementation of external circumstances may be interrupted algorithm and generates with the environment and time for a change in the output function. With the application of these characteristics is uncertain. It is difficult to find a meaningful general classification software applications (Law). With the increase in plexity of the software, the full and plete separation would not exist. Below the software described the breadth of potential applications software. System software System software for other services the procedures set procedures. Some system software (for example, the piler, editor and file management utility) dealing with plex information structure but identified. Other applications (such as operating system ponents, drivers and remote munications processors) to deal with a large number of nondeterministic data. No matter under what circumstances, the system software is characterized by: frequent interaction with the puter hardware。 Demand scheduling, resource sharing and management of the plex process of concurrent operation。 Or adapted to cope with the purchase of new hardware. These are generally referred to as software maintenance. Software maintenance costs in the energy, its alarm rate to the frequency of troubleshooting source. But even worse is that many of the personal characteristics of procedures they have in fact made it is impossible to maintain. This appeared software crisis. The development of puter systems from the third era began in the mid1970s until now: Distribution System more puters, with various puter operation and mutual munication greatly increased the plexity of puter systems. Global works and local area works, broadband digital munications and the growing of the instant data access request, the software developers raised very high demands. Many personal puter software panies has been the driving force for development. Despite the second era of software panies sold only a few hundred, a few thousand sets, the third era of software panies have sold tens of thousands, even hundreds of thousands of sets. Personal puter hardware will soon bee a modity, and puter software will enable the characteristics are different. In fact, in the mid1980s, when the personal puter sales growth rate tends to slow, sales of software products still continue to grow. Many people spent on household and industrial use of the software purchase money than necessary puter software more money. The fourth puter software era has just begun. Feigenbaum and McCorduck [FEI83] These authors predicted: fifthgeneration puter and related software in the world will be on political power and the balance of industrial power have a farreaching impact. The fourth generation of software development technology (4 GT) is changing the software in the Community of certain sectors of the puter program design methods. Expert systems and artificial intelligence software has been the ultimate laboratory to the people from the reality of the problems in the practical application. With the era came to the fourth, the software crisis continues to deepen. Now we can describe software crisis following ways: 1. Hardware plex procedures have been beyond our hardware design to the development potential of software capabilities. 2. The design of the new procedures failed to keep pace with the ability of the new procedural requirements. 3. Maintenance has been the ability of poor design and lack of resources threats. As a so