CSC/ECE 517 Fall 2009/wiki3 10 OT

Topic : CRC cards are useful, but have some limitations. For example, they require that a group be present; it is sometimes hard to get a group together. One alternative technique is "Object Think." Compare CRC cards with Object Think and any other alternatives for the first stages of analysis and design.

Object Think

Simon Horwith defines “Object Think” as an approach to Object Oriented Programming based on the practice of object personification.

Object Think represents a way to think of the domain model in terms of objects, which further helps in developing or designing classes. Object Think was suggested as a practical alternative to CRC cards in 1993 by Coad and Nicola. The primary benefit of Object Think is that unlike CRC cards, it can be done individually and no group is required.

In Object Think perspective, objects are modeled to carry out real world functions. Then the responsibilities are distributed across objects as part of the design. Object Think therefore helps to create an accurate domain model where every object in the domain model handles all of its own responsibilities. The advantage of this approach is that as the software system is initially designed, the designers might start with fewer objects carrying out many functionality. As the system grows over time, Object Think will lead to design a community of objects sharing those responsibilities.

Object Think also bridges the traditional process-oriented thinking with the object mindsets. For example, the real world scenario of communication translates to Messaging in the Object Oriented paradigm.

Object Think perceives Objects as independent entity performing actions and making decisions on its own. Mike Abney, in the article -"Object Think: A Perspective on Objects" suggests that an object's capability to act is one of its three categories of responsibilities: "whom I know," "what I do," and "what I know." Peter Coad and Edward Youdon (in Object-Oriented Analysis, 2nd ed., Prentice Hall, 1990) refers this to object's services. Although technically services refer to an operation or procedure, when an object performs the services they are viewed as actions on the objects. As an example, an account object provides a debit method. So, when the debit method is acted on the object, it is viewed as debit action being carried upon the object. This means the state of the object changes based on the action that is being performed on the object.

Guildelines for design using Object Thinking

1. Everything in the domain model is an object. This means that a class technically cannot have free-floating functions that are not related to an object of the class. Functions generally represent the actions on an object or a concept in the domain model. So, they have to be associated with an object that represent the concept

2. Think like an Object

3. Model the objects of a system using the language of the domain model. This helps designers to focus on the domain model and design a system with a high level perspective instead of bogged down with low level implementation details.The purpose and capabilities of an object has to be designed and stated clearly. Also, the implementation should statisfy the stated goal.

4. Objects should have context free behavior - This really means that Objects should be designed with the object oriented principles like encapsulation, cohesion, coupling, reuse etc. and Objects should be modeled as autonomous agents that perform the operations in isolation.

5. Design using simulation - Simulating a domain model by representing it in terms of various objects will help to identify the details of the design.

6. Design to keep functions and data together - Domain model's operations can be represented as actions on objects. Since these operations affect the state of the object, it is a good practice to tie objects and their operations together.

Benefits of Object Thinking

1. Unlike CRC, Object thinking can be carried out by individuals

2. Design using Object think provides a maintainable code as in a long run, a system will have objects sharing ther responsibilities and collaborating to complete a domain operation

3. Design using object think also results in a reusable code

4. Since Object Think insists on stating the purpose and capabilities of the objects, this will result in a better definition of data and the responsibility on the objects

5. Also, Object Think can be used as a platform to educate developers to become object oriented thinkers

References

Object Think - Common Sense Software Architecture by Simon Horwith on cfunited conference 2006

Object Think: A Perspective on Objects by Mike Abney on http://www.informit.com/articles/article.aspx?p=25184&seqNum=4

http://net.educause.edu/ir/library/text/c95/c95-ps04.txt

http://corfield.org/blog/index.cfm/do/blog.entry/entry/Object_Think