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Separation of issues is an important design concept, leading to the use of entity, boundary and control objects 

It is good object oriented design to provide two additional object types, as well as the normal business objects.  A boundary object is used to provide the interaction between a user and the system- with normally one boundary object per Use case.  A control object is design to provide the control for the transaction and normally sits between a boundary object and the remaining objects.  The real substance of the system- the objects which do the work and hold the data, are known as entity objects.

Introduction to components and nodes 

Components and nodes are means of implementing classes, combining them together into physical implementation units and deploying them across one or more system nodes.

The importance of different system architectures in implementing a specification 

Systems can be implemented across a range of architectures where the issues of mixing client-based or server-based implementations is dependent upon a range of issues including cost of infrastructure, cost of development and ease of development.