Example of Design Pattern:

Classification and intent:

Composite is a structural design pattern. Its intent is to compose objects into tree structures to represent part-whole hierarchies. It lets clients treat individual objects and compositions of objects uniformly.

Motivation:

Lesson presenter/planner of an educational system for individualized learning may decide to build an agenda of the topics to be presented during the lesson. Complex topics can be divided into simple elements like concepts, text, graphics, and the like, or into a sequence of subtopics. Each subtopic can be further divided into a lower level of sequence of simple elements and other subtopics, producing an agenda like in the following example:

1.   Topic  1
      Text
      Graphics
      Concept A
      1.1      subtopic1.1
      1.2      subtopic1.2
                Text
                Concept  B
                1.2.1    subtopic    1.2.1
                1.2.2    subtopic    1.2.2

2.    Topic  2