This chapters shows off some more complex association mappings. The following model of the relationship between Employer and Employee uses an actual entity class (Employment) to represent the association. This is done because there might be more than one period of employment for the same two parties. Components are used to model monetory values and employee names. Heres a possible mapping document: employer_id_seq employment_id_seq employee_id_seq ]]> And heres the table schema generated by SchemaExport. Consider the following model of the relationships between Work, Author and Person. We represent the relationship between Work and Author as a many-to-many association. We choose to represent the relationship between Author and Person as one-to-one association. Another possibility would be to have Author extend Person. The following mapping document correctly represents these relationships: ]]> There are four tables in this mapping. works, authors and persons hold work, author and person data respectively. author_work is an association table linking authors to works. Heres the table schema, as generated by SchemaExport. Now consider a model of the relationships between Customer, Order and LineItem and Product. There is a one-to-many association between Customer and Order, but how should we represent Order / LineItem / Product? I've chosen to map LineItem as an association class representing the many-to-many association between Order and Product. In Hibernate, this is called a composite element. The mapping document: ]]> customers, orders, line_items and products hold customer, order, order line item and product data respectively. line_items also acts as an association table linking orders with products.