What are the Key Concepts?

OT models systems using 2 key concepts:
 

1. It defines the business world (or domain) that a system encompasses in terms of objects.
   • Objects may be physical objects (a car) or abstract ideas (commission scheme) or events (a delivery).
2. It classifies the objects into similar concepts by looking for their common characteristics (or properties) and groups them into hierarchies.
   • Common characteristics need only be defined once.

Principles

In order to then build the system, OT uses 4 key principles:
 

1. Abstraction - the describing of objects by defining their unique and relevant characteristics (properties).
   • Whilst an object may have 100s of properties normally only those properties of importance to the situation are described. (e.g. life policies premiums are normally important; whereas the time of day a policy was purchased is not usually of value).
      
2. Encapsulation - the decoupling of the external use of an object from the object itself.
   • Objects have behaviours (e.g. formula to work out monthly premium) with individual behaviours called services (e.g. provide monthly premium). Services are invoked by sending messages (inputs) which in return produce output. Involving a service causes a state change (e.g. monthly premium has been paid). Encapsulation leads to more stable systems.
      
3. Inheritance - Inheritance is the ability to write one definition as an extension of another.
   • Only the properties and behaviours which are different need be described in the child object. (e.g. a monthly savings plan and a single premium bond have different collection frequencies). All the properties and behaviours which are unchanged are obtained by reference to the parent.
      
      
4. Polymorphism - the ability to make one object able to be coupled with a wide variety of others, relying on their all having a common external interface.
   • Polymorphism separates the different uses of an object (e.g. print text from print a drawing). New uses (e.g. print a picture) can be added with no impact on the existing uses of the object.

This can get rather technical, so don't worry if it seems obtuse. For those that are interested in knowing more, there are links at then end of the page.

Next is What are the Benefits, especially in respect of SIM?

JS

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