Identify Structures

Structure

A structure is a manner of organization which expresses a strong semantic organization within a problem domain.

Types

There are 2 types: 1. Generalization-Specialization (Hierarchy) 2. Whole-part (Aggregation)

Define Attributes

When defining attributes of objects, remember to define them in such a way that the system needs it and there is no other way of knowing those attributes.

Problems

There are some problems that need to be addressed while defining the attributes. 1. An attribute which varies with time should be replaced by class with effective date and time. e.g. Price of an item. 2. An attribute which can have multiple values should be replaced by a class with object connection. 3. An attribute of a boolean nature should be named something like status. 4. If there are common attributes between the classes then they should be abstracted away into a common generalized class.

Show Collaborations

This is the 2nd step of evaluating the responsibilities of an object.
It can be done through 8 sub-steps: 1. For an actors, include an object connections to its participant ( #association). 2. For a participant, include an object connections to its actors and its transactions. 3. For a location, include object connections to the objects it can hold ( #association), to its part objects ( #aggregation) and to the transactions which take place at that location. ( #association). 4. For a transaction, include connections to its participant, subsequent transactions ( #aggregation) and its line items ( #aggregation). 5. For a line item , include connections to its transactions, its items ( #association), an item description object ( #association) and a subsequent line item ( #association). 6. For an item, include connections to its line item and item description object ( #association). 7. For a composite object, include connections to its parts ( #aggregation). 8. For all the objects mentioned above, include connections to objects which either receive messages from them or sends messages to them ( #association).

Define Services

This is the 3rd and last step in defining the responsibilities of an object, that is to define what services it provides.
While establishing the services for the objects, following fundamental questions need to be asked: 1. Why does the system need this object? 2. What useful questions can it answer? 3. What useful action can it perform? 4. What this object can do, based upon what it knows? 5. What this object can do, based upon whom it knows? 6. What calculations can it do? 7. What on going monitoring it can do? 8. What calculations across a collection could it make (letting each worker do its part)? 9. What selections across a collection could it make (letting each worker do its part)?