Instead of storing duplicate data for each object, you can make an association in relational databases with a “foreign ID.” The foreign ID refers back to the primary object, but it doesn’t store any information about the foreign object. Therefore only one object needs to be aware of the relationship. A relational database schema includes tables, each containing rows and columns. Columns represent attributes for the table, and rows represent an instance of that object. If an object has a foreign ID, the table will store this information in a column.