Products and Contributors

A product is a thing which can be sold or contributed to. _Examples of products include books, games, podcast, software product._ 
Each product has:
* title;
* subtitle;
* web page where people find info about the product;
* type (book, game, software product);
* brands;
* parent product. _Example: an original version of a book to a translated version_

A contributor is a person or an organization which invest its money or time to develop a new product or to improve an existing one. Each contributor has a role he played in contributing to a product.

For parent/child products a contributor can play two roles at once. _Example: Vladimir Livshits translated “How to Change the World” into Russian. For original version of the book he made a Russian translation. For Russian version of the book he made a translation._