中文摘要：

为解决普通用户对XML文档的近似查询问题,提出了一种基于文档属性单元松弛的XML近似查询方法.该方法将XML文档中的叶子结点和属性结点作为属性单元处理,基于一致集的概念导出最大集,生成最小非平凡函数依赖集,从而找出属性单元之间的近似函数依赖关系,进而求出近似候选码和近似关键字.在此基础上,根据属性单元支持度将属性单元按重要程度排列并据此对初始查询条件进行松弛,最不重要的属性单元最先松弛并且松弛程度最大.利用松弛后的查询条件对XML文档进行查询,可得到与初始查询条件近似的查询结果.实验结果和分析表明：提出的XML近似查询方法能够很好地满足用户的查询意图,具有较高的执行效率.

英文摘要：

To deal with the problem of approximate query against XML documents,based on the extensions of document attribute units,the authors propose a novel XML approximate query approach which can provide the relevant query results to the user＇s original query.The leaf nodes and attribute nodes of XML documents are treated as attribute units.Then based on the concept of the agree set,the maximum set is exported and the minimum nontrivial functional dependence sets are generated consequently.Thus the approximate dependence relations can be found.By using the approximate dependence relations,the approximate candidate keys and approximate keywords are found.After that,this approach ranks the attribute units according to their supported degree and expands the original query by regarding the importance sequence of attribute units.The first attribute unit to be relaxed must be the least important attribute unit and has the maximum relaxation degree.The relaxed query is used to query the XML documents and the relevant query results of the original query are obtained.The experimental results and analysis demonstrate that the XML approximate query approach presented can efficiently meet the user＇s query intentions and has a high performance as well.