模型中各系数与运行工况有关，可根据当前的汽包压力、锅炉物理结构数据及水蒸汽性质得到。
The parameters of the model can be obtained from the pressure in the drum, the physical dimensions and characteristics of the boiler and the steam and water parameters table.
这个特点与非dbms系统非常不同，在那种系统中，程序员必须知道数据的物理结构。
Compare this with non-DBMS systems in which the programmer must know the physical structure of the data.
这些文档的物理结构—兄弟元素的次序、数据是存储在属性中还是在PC DATA元素中、是否使用实体—往往是不重要的。
Their physical structure — the order of sibling elements, whether data is stored in attributes or PCDATA-only elements, whether entities are used — is often unimportant.
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