Now, you need to let the Tapestry engine know about this implicit mapping, by making it explicit.
现在，需要通过显式化，让Tapestry引擎知道这个隐式映射。
By making a view, rather than an explicit table, we avoid the main disadvantage of a vertical schema, namely that many queries require it to be joined with itself, which can be expensive.
通过定义视图而不是显式的表，可以避免垂直模式的主要缺点，即许多查询要求它与本身进行联结，而这种操作是很昂贵的。
Making explicit domain assumptions underlying an implementation makes it possible to change these assumptions easily if our knowledge about the domain changes.
在实现时，使领域假设显性使得容易的改变假设变得容易，如果我们关于领域的知识改变了。
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