Creation

Now that we can define the objects (though not rigourously, that's coming later), we need to know how to create them. Obviously, object creation could possibly mean invoking the database for lookups and the like, so it needs to be well abstracted. In this case, we'll use the abstract factory pattern to create factory objects which will create our entities. For example, if you define the following entity:

class PersonAtAddress(Entity):
name as Name
ssn as SSN
birthday as Date
address as Address

Then you will end up with the following abstract factory

class AbstractFactory:
def getNameFactory:
...
def getAddressFactory:
...
def getPersonAtAddressFactory:
...

class PersonAtAddressFactory:
def Create(name_key as Name.ID, ssn as SSN, birthday as Date, addr_key as Address.ID):
...

Now, we have a consistent, programmatic way to create entities. We can wrap these calls in CORBA or SOAP or whatever, but the foundation is solid.

Next time, we'll start looking at how the objects map to a relational database.