Common Mechanisms of UML

Object Diagrams

• Object diagram is a set of objects and their relationships
• Graphically, a class diagram is a collection of vertices and arcs

Contents
Object diagram contains

• Objects
• Links

Uses

• To model a snapshot of a set of objects in a system at a given point in time
• To model an instance of interaction diagrams

Common Modeling Techniques
Modeling Object Structure:

• Decide on the mechanism to model
• A mechanism refers to some function or behavior of the system achieved through the interaction of a set of cooperating classes, interfaces, and other things 

• Build a collaboration to explain a mechanism
• Find out the classes, interfaces, and other elements that take part in this collaboration and the relationships among them
• Consider one scenario that walks through this mechanism
• Using a snapshot of the scenario, show each object that participates in the mechanism
• Show the state and attribute values of each such object to understand the situation
• Likewise, expose the links among these objects, that represent instances of associations among them

Reverse Engineering
To reverse an object diagram:

• Select the target to reverse engineer
• Usually, the context is inside an operation or relative to an instance of one particular class
• Using a tool or walkthrough freeze execution of a scenario at a certain point in time
• Check out the set of objects that collaborate in that context and depict them in an object diagram
• To understand their semantics better, expose these objects states
• To understand their semantics, find out the links that exists among these objects
• If the diagram becomes complex, simplify it by eliminating objects that are not significant in the scenario
• As necessary, expand the neighbors of the objects and expose the state of each object in more detail
• Structure needs to be added or labeled, which is not clear in the target code
• The missing information explains the design objective