Note that there should one provider per repository - if the list contains multiple providers that works for the same repository, the order becomes important as the first one matched will be used.
The body of the relation usually contains the correspondences that need to be applied to the properties of the matched values, in order to propagate the execution of the transformation.
关联的主体通常包含需要用于匹配的值属性的通讯,这样可以传递转换的执行。
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Note that because you don't specify a type for the pattern-matched case, anything will match and the message is bound to the MSG name (which you need in order to print it).