WHAT IS A ALEXANDRIAN FORM OF A PATTERN?

Alexandrian form

The pattern name : A name by which the pattern is called. For example, we might create a pattern called `C++ Type Promotion,' just so we can refer to it conveniently.
The problem the pattern is trying to solve : If people know what problem the pattern solves, they'll know when to apply it. For example, Type Promotion solves the problem of promotion between objects of different C++ types, zero or one of which is a built-in type, or a type exported by a library for which the programmer does not have source.
Context : A pattern solves a problem in a given context, and it may not make sense elsewhere. For example, C++ type promotion applies to C++, and potentially to other object-oriented languages with strong compile-time type systems; the decision of which promotion to apply is made at compile time; and the context is inadequate to apply built-in translation rules (e.g., from a derived class to one of its public base classes).
Forces, or tradeoffs : Not all problems are clear-cut. Forces make clear the intricacies of a problem. For example, in Type Promotion , we need to point out the tension between using constructors and using conversion operators. We must also point out that we can redefine some properties for class types that we cannot redefine for built-in types. A good pattern resolves one or more forces.
Solution : This describes the structure, behavior, etc., of the solution, which is often tantamount to telling how to build the solution. For Type Promotion , a program should promote class objects to built-ins using a member conversion operator, and should use constructors for all other promotions.
Examples : are present in all good patterns. Visual analogies are also powerful and frequent adornments for a pattern: you can draw a picture for most (but not all) good software patterns.
Force resolution, or resulting context : Few patterns are perfect or stand on their own. A good pattern tells what forces it leaves unresolved, or what other patterns must be applied, and how the context is changed by the pattern.
Design rationale : This tells where the pattern came from, why it works, and why experts use it. Good designers are most effective when they apply patterns insightfully, and that means being able to understand how the patterns work.