You can find the first part of what promises to be a very educational series over here: http://blogs.msdn.com/adonet/archive/2007/01/30/entity-data-model-part-1.aspx.
One of the things that I love about this technology is how crisp it is about defining separately elements that are independent. This article, for example, focuses on conceptual associations, entity types, their properties. In the next post (according to the last paragraph at least), entity sets and association sets are introduces. These are related, but not strictly the same; they are therefore declared in separate elements in the model.
There are more bits like this that I will point out just because I find them interesting, where different concepts are given independent forms of declaration and thus introduce the possibility of better clarity, greater reuse and more flexible mappings.