software architecture slide 3

6 differences between layer and tier

　　tier 是物理上的分离

　　layer是软件元素的分离

5 how many patterns can be used in a complex system?

　　Mulitple patterns can be used in architecture design of a complex system.

4 what is the relationiship between tactics and patterns?

　　Most of patterns consists of (are constructed from) several different tactics. 

　　Tactics are building blocks of design from which architectural patterns are created.

3 How to do architectural design?

　　Architectural design seldom starts from first principles. Experienced architects typically think of creating an architecture as process of selecting, tailoring, and combiing patterns.

2 where do patterns come from?

　　Patterns are found in practice, not invented, they are discovered.

　　　　There will never be a complete list of patterns. Patterns spontaneously emerge in reaction of environmental conditions, and as long as those conditions change, new patterns will emerge.

1 what is an architectural pattern?

　　An architectural pattern

　　　　is a pacakge of decisions that is found repeatedly in practice

　　　　has known properties that permit reuse and

　　　　describes a class of architectures