Google Code University
From Introduction to Databases and MySQL:<p><i>Such keys make it possible to relate the tables to one another, so we can, for example, find the customer information given a key value in the order table. A foreign key is a key used to link two tables together. Typically you take the primary key field from one table (customer) and insert it into the other table (order) where it becomes a foreign key (it remains a primary key in the original (customer) table). This type of structure is called a relational database: we have multiple tables that connect to one another via keys.</i><p>It's really jarring to see such wrongness published under the banner of "Google Code University." I've come to terms with the fact that in the minds of most web/MySQL programmers the term "relational database" means graph/network database. But I still don't expect to see it published by the denizens of a top engineering firm that hires only the best and brightest.