What do Gamma et al. suggest are the four essential elements of a design pattern?

What do Gamma et al. suggest are the four essential elements of a design pattern?

Answer: 1. A name that is a meaningful reference to the pattern.

2. A description of the problem area that explains when the pattern may be applied.

3. A solution description of the parts of the design solution, their relationships, and their responsibilities. This is not a concrete design description. It is a template for a design solution that can be instantiated in different ways. This is often expressed graphically and shows the relationships between the objects and object classes in the solution.

4. A statement of the consequences—the results and trade-offs—of applying the pattern. This can help designers understand whether or not a pattern can be used in a particular situation.