The xsd:choice data type describes a structure in which only one of its child elements can be active or selected.
choice 数据类型描述了这样一个结构，其中只有一个子元素可以是活动的或者可供选择。
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Active fuzzy data model is studied based on relation data model. Following an introduction to active fuzzy database technology, the structure of active fuzzy database is analyzed.
Through the observational data which was transmitted back to the ground by space telescopes, we have seen many kinds of the three-dimensional structure of the active phenomena in solar atmosphere.