What is the best way to represent an album and song entity in an e-commerce schema?
There really is not a One True Answer, but there are plenty of samples available on the web.  One site is: http://www.databaseanswers.org/data_models/

This is actually a site with many simple data models. I would not call these a complete solution, but it is a good resource for getting started.

For a CD Collection there is a sample model, that focuses on content, not on the commercial side of selling content.

http://www.databaseanswers.org/data_models/cd_collection/index.htm

In addition if you search for something like example database model music you will find other examples.