This is the data model for the Chinook Database, which supports a fictitious music e$-$commerce site. Each track is stored in a particular digital format and has an associated genre. The site also supports playlists, where one single track can be part of multiple playlists but may not be included in any playlist. Each customer order is memorialized in an Invoice which is composed of one or more InvoiceLines, each representing one track purchased. Note that the Quantity attribute of InvoiceLine indicates the number of copies of the particular track that was purchased as part of the associated invoice. Every customer is assigned an employee representative, and each employee is supervised by another employee. Since the CEO does not report to another employee, this is stored in the database as the CEO reporting to themselves.