As we read in Oppel and Sheldon (2009), an entity is "[a] person, place, thing, event, or concept about which data is collected, such as a recording artist, a book, or a sales transaction."
We also noted in Database Principles (in Welling and Thomson, 2001), that a relationship is a "link between tables; can be one-to-one, one-to-many, or many-to-many, 'according to the number of things on each side of the relationship.'" Strictly speaking, a many-to-many relationship is not permitted in an ER diagram or in any database schema.
"In a many-to-many relationship between Table A and Table B, each row in Table A is linked to 0, 1 or many rows in Table B and vice versa. A 3rd table called a mapping table [or, bridging table] is required in order to implement such a relationship. (www.databaseprimer.com)
Let us now take a look at an ER diagram of a relational database (that is, one with multiple tables and relationships between them) and see what we can tell about it upon closer examination.
Figure 17: ER diagram from our James Bond database (November 2016)
Figure 18: Information Engineering style of how to depict cardinality.