Let us imagine that we want to build a simple PhoneBook application, capable of storing a set of contacts for each registered person. A person has a name and each contact is represented by a name and a phone number.
The domain model of the PhoneBook application consists only of three entities: PhoneBook,
Person and Contact. The PhoneBook entity represents the class that knows all registered people.
Each person maintains his/her own set of contacts.
Using the DML, we could textually describe the domain model of our PhoneBook application through the following DML code:
1. class PhoneBook;
2.
3. class Person {
4. String name;
5. }
6.
7. class Contact {
8. String name;
9. String phoneNumber;
10. }
There are other business rules that should be implemented. For instance, consider that it
should be possible to remove a Contact given its name, and getting all Contact instances
whose name contains a given substring. These would correspond to the implementation of
methods in the Person class with the desired functionality.