| Alfalfa is widely grown as a forage crop due to its good quality characteristics and high adaptability. Alfalfa has a long history of being cultivated in our country, and it is called 'the King of forages' because of its good economic and ecological benefits. In the world, China is one of the largest countries for the planted alfalfa area. As a large Province of planting alfalfa, in Gansu it plays an important role in daily life for most of farmers and agricultural technicians. However, alfalfa disease not only reduces its yield and edibility, but finally causes certain harm as well through direct or indirect interactions with animals and human beings. Therefore, the study of an expert system based on specialists' intelligence and experience in disease prevention has a very significant meaning for improving alfalfa yield and increasing income of farmers.Based on the characteristics of alfalfa diseases, three knowledge acquirement approaches of traditional manual knowledge acquirement, automatic knowledge acquirement and semiautomatic knowledge acquirement were analyzed and compared. In this system GIS-based semiautomatic knowledge acquirement was selected as the knowledge acquirement, and traditional knowledge expression approach was chosen as knowledge expression method. Knowledge base is a core of any expert systems, and its creation is one of "bottle neck" problems. In the process of creating diagnosis base for alfalfa diseases, three approaches of literature search, visiting related field experts and field investigation were integrated applied, and the database of alfalfa diseases with spatial geographic attributes in Gansu Province was constructed. In area of reasoning mechanics, it is classed according to the knowledge expression character of alfalfa diseases, whether the reasoning process of solving a problem has applied revelatory knowledge, and whether a result is precise. By taking easy use and understand for farmers into considerations, an integrated approach of combining with positive and reverse reasoning was used in this system. Under the environment of VB.NET in Visual Studio 2005 .NET software package and embedded Mapobjects2.3 component, the alfalfa disease diagnosis expert system was designed and developed. By means of interface programs, the functions of zoom in, zoom out, pan and etc. for a map were realized.The following findings were achieved in this research: 1) based on soft project principle, database technique and expert system principle, the design of alfalfa disease diagnosis expert system in Gansu Province was finished, and the major program codes of key modules and components were developed. 2) The spatial distribution database of alfalfa diseases in Gansu Province was constructed using ArcGIS 9.1 and Access 2003 by consulting reference, visiting related filed experts and investigating in the filed. 3) on the basis of systematically analyzing traditional manual knowledge obtainment, half-automatic knowledge obtainment and automatic knowledge obtainment, the GIS-based half-automatic knowledge obtainment technique was used to acquire knowledge of alfalfa diseases. 4) the knowledge source was verified repeatedly by the related field experts, and it accumulated knowledge and experience of experts who have been worked in alfalfa diseases for many years. So it is close to real situation, and it may be used to direct practice. 5)for knowledge base maintaining, the knowledge bases in this system were constructed by Access 2003, the knowledge updating, such as appending, deleting and modifying a record, could be finished by varied approaches, and its expansion is simple, which a knowledge base could not only be maintained by itself, but updated by other programs as well. |
