# Understanding OR mappings

The Dali OR (object-relational) Mapping Tool allows you to describe how your entity objects map to the data source (or other objects). This approach isolates persistence information from the object model–developers are free to design their ideal object model, and DBAs are free to design their ideal schema.

These mappings transform an object data member type to a corresponding relational database data source representation. These OR mappings can also transform object data members that reference other domain objects stored in other tables in the database and are related through foreign keys.

You can use these mappings to map simple data types including primitives (such as `int`), JDK classes (such as `String`), and large object (LOB) values. You can also use them to transform object data members that reference other domain objects by way of association where data source representations require object identity maintenance (such as sequencing and back references) and possess various types of multiplicity and navigability. The appropriate mapping class is chosen primarily by the cardinality of the relationship.

Mapping an entity