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农产品市场价格web信息分析方法研究
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摘要
近年来,我国农产品市场价格呈现的异常波动已成为社会关注的焦点。农产品价格波动不仅会对农民收入和农民生产积极性产生直接影响,更关乎百姓的日常生活和切身利益。为保持经济平稳健康发展、保障群众生活,稳定物价的宏观调控尤为重要。价格监测和预测是维持价格稳定的一个重要环节,精确地价格监测和低误预测是涉农科研工作者的一个重要研究方向。我国农产品市场价格Web信息分布广、更新快,迫切需要建立一套垂直搜索引擎系统实现定期抓取网络中农产品价格数据,迫切需要建立一个农产品价格分析、预测和监测平台,提供全面、清晰的分析结果。为政府部门管理人员提供生产调控、决策分析的依据,成为农民种植植物的决策依据,为农产品市场价格稳定做出积极的贡献。
     某些农网等价格信息网提供的农产品价格信息有数据单位不统一、产品名称不规范等问题,经过对分布在不同网站上的农产品市场价格数据的分析和总结,提出了规范产品名称、规范市场名称、初始化农产品类别、初始化省市、规范数据单位、去重策略选择和零价格数据处理7个数据规范化原则。研究了DOM树方式、正则表达式、HTMLParser提取网页文本信息,利用Heritrix等软件搭建了农产品市场价格垂直搜索引擎系统实现了抽取不同农网上的价格信息,经规范化后形成了统一、完整的SQL server农产品价格数据库。
     为进一步提高农产品市场价格预测精度,及时发现价格异常的农产品,选取了山西晋城绿欣农产品批发市场胡萝卜、白萝卜、大白菜、大葱、豆角、黄瓜、尖椒、韭菜、茄子、青椒、土豆、西红柿和油菜十三种农产品进行预测算法对比研究。在加权算术平均预测法中对比分析了5种权数设置方法,实验结果表明以当年价格为权数误差最低,优于其它权数设置方法,在平均数预测法中优于简单算术平均法;对比分析了时间序列非季节11种预测方法,研究结果表明二次曲线趋势延续法和龚伯兹曲线趋势延续法不适用于农产品价格预测,在简单算术平均法、加权算术平均法、时间序列平均增长量预测法、时间序列几何平均法、一次移动平均预测法、二次移动平均预测法、一次指数平滑法、二次指数平滑法和直线趋势延续法9种预测方法中二次移动平均预测法和二次指数平滑法误差低于其它预测方法,适用于农产品价格预测,在此基础上提出了一种改进的二次指数平滑预测法,二次指数平滑预测法中一次、二次平滑系数不同时,所有的误差平方和都小于或等于一次和二次平滑系数相同时的误差平方和。改进后的二次指数平滑预测法误差最低,优于末改进的二次指数平滑法,也优于二次移动平均预测法;对比了时间序列季节指数水平法和季节指数趋势法,从实验结果中可以看出,大多数农产品两种预测方法误差平方和相差很多,实际预测价格可以采用误差平方低的预测值;在价格异常农产品判定方面提出了从预测值与实际价格误差平方和历史误差2种排名方式,确定当月价格异常农产品和确定去年价格异常,今年价格仍然异常的农产品的判定方法。
     目前与农产品价格有关的信息网站大多只提供了原始价格信息显示,针对规划好的从不同网站抓取出的价格数据利用企业级工作平台MyEclipse开发出了农产品市场价格Web信息分析系统,实现了价格查询、价格分析、价格预测和价格监测等功能,价格分析功能包括价格走势、各省对比、品种对比、同比环比和市场对比,价格预测功能包括单值预测和趋势预测,各省对比包括某一天对比和某一段时间对比等,分析结果以折线图、柱形图或地图的形式显示,界面美观,功能实用。可满足农业管理部门、农业企业、农户准确掌握不同地区、不同农产品价格的变化动态与走势的需要。
In recent years, the abnormal fluctuation of market price of produce has become a focus of attention in our society, which not only has a direct influence on farmers'income and their enthusiasm for production, but also plays an important role in common people's daily life and their vital interests. A macro-management of prices is especially important to ensure a stable and healthy development of economy and to secure people's lives. The prediction and monitoring of price is an important element to maintain a stable price, at the same time a precise monitoring as well as a prediction with low error rate is an important part for agricultural research. It is urgent to establish a vertical search engine system to regularly record produce's prices on the Web because the information there is usually widely distributed and quickly updated in our country. A platform to analyze, monitor and predict produce's price is imminently needed so as to provide comprehensive and clear results for the reference of governmental production regulation and decision-making, as well as farmers' planting, and to make a contribution for the stability of produce's market price.
     The information released by some agricultural website has the problem of non-standard product name and non-uniform data unit. Through the analysis of market price of various produce from different websites, the research puts forward the following7principles, such as the standardization of produce name, that of market and data unit, the initialization of produce categories and provinces, the choice of a material-removal strategy and data processing of a price around zero, studies the tree system of DOM, the regular expression, extracts text messages from the Web through HTMLParser, establishes a vertical search engine system by taking advantage of softwares such as Heritrix, and finally forms a unified and integrated price-database of produce in the form of SQL server.
     In order to improve the prediction accuracy of produce's market price and timely find the produce with an abnormal market price, the research selects carrots, white turnips, Chinese cabbages, green onions, kidney beans, cucumbers, Chinese chives, eggplants, peppers, green peppers, potatoes, tomatoes and rapes to make a comparative analysis with prediction algorithms. Meanwhile, the methods to set up5kinds of weights are comparatively analyzed with the weighted arithmetic average prediction, the experiment results show that the latter is better than the other five methods if current year's prices are taken as with the lowest errors of weights, and the prediction with mean value is superior to a simple arithmetic average method. In addition,11different kinds of time-series non-seasonal exponential prediction methods are also studied, the results show that the curvilinear trend duration method of B-Gompartz and double exponential are not suitable for the prediction of produce's market price, among the methods of simple and weighted arithmetic averaging, of series with an average increment and with geometric averaging, of single and double moving averaging, of single and double exponential smoothing and of a rectilinear trend duration, the double moving averaging and the double exponential smoothing are superior to other methods and suitable for the prediction of produce's market price for their lower errors. On the basis of the experiment results, the research puts forward an improved prediction method of double exponential smoothing which is superior to the previous one and the double moving averaging for its lowest errors, when there is a different quotient of single and double exponential, all the sums of squared errors is no more than those when there is the same quotient. At the same time, the research compares the horizontal prediction and the tendency prediction with seasonal indices, the results show that there is a distinct difference between the sums of squared errors with these two methods, and the actual predictive price should be predicted with the lower squared errors. As to the determination of produce with an abnormal price, the research puts forward two methods, that is, the squared errors of predictive price and actual errors as well as historical errors, so as to determine the produce with monthly abnormal price and that with an abnormal price last year and this year.
     Websites which provide produce prices usually give an initial price. On the basis of data taken from various websites, the research develops a Web-based analytic system of produce price with the help of MyEclipse enterprise workbench so as to achieve the function of price search, price analysis and price prediction, and so forth. The function of price analysis includes the analysis of price trend, the comparison of price from different provinces, that of different varieties, that of chain relative and year-on-year ratio and that from different markets. The function of price prediction includes the prediction of unit value and that of trend, and the comparison of price from different provinces includes the comparison of price of a certain day and within a certain period of time, and so on, meanwhile the analytic results are shown in the form of line charts, bar charts or maps with a beautiful interface and a practical function. The intelligent Web information analysis method of market price of various produce can help the agricultural administrations, agricultural enterprises and farmers master the variety of price and the tendency of different regions and different produce.
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