Attributes can't contain other elements. White spaces can't be ignored in attributes. Attribute values are harder to search for in search engines. Attribute values often don't appear on the screen in editing tools. Attributes can be slightly more awkward to access in processing API's.
Attributes are unordered.
Example 1 - Books 1. The only important thing is that the object is a book. Encoding of a title inline, where the title will be printed as part of the paragraph. The Authors name can be extracted for use in index lists etc. An example of the two extremes in object modeling.