The SQL repository allows you to define multiple named item types. Each item type is defined by an item descriptor. You can define different kinds of objects with different item descriptors, and ATG will manage them in a single repository. Each named type corresponds to an item descriptor, and each item descriptor corresponds to a RepositoryView of the same name.
For example, suppose we have a simple database with two kinds of entities: book and author. A book has exactly one author, and an author has zero or more books. This is depicted in the figure below.
DAF lets you represent this in a single repository using two independent types named book and author. They are independent in that they do not share any properties in their item descriptors. They may happen to each have properties like name or weight, but their properties are independently defined. Another way to look at it is that they each have their own item descriptor.
The SQL repository also supports a simplified form of inheritance for item descriptors. See Item Descriptor Inheritance in the SQL Repository Data Models chapter.
