Software design vs. software architecture

Question

Could someone explain the difference between software design and software architecture? More specifically; if you tell someone to present you the 'design' - what would you expect them to present? Same goes for 'architecture'.

My current understanding is:

design: UML diagram/flow chart/simple wireframes (for UI) for a specific module/part of the system

architecture: component diagram (showing how the different modules of the system communicates with each other and other systems), what language is to be used, patterns...?

Correct me if I'm wrong. I see Wikipedia has articles on http://en.wikipedia.org/wiki/Software_design and http://en.wikipedia.org/wiki/Software_architecture, but I'm not sure if I have understood them correctly.

Answer 1

Yep that sounds right to me. The design is what you're going to do, and architecture is the way in which the bits and pieces of the design will be joined together. It could be language agnostic, but would normally specify the technologies to be used ie LAMP v Windows, Web Service v RPC.

Answer 2

You're right yes. The architecture of a system is its 'skeleton'. It's the highest level of abstraction of a system. What kind of data storage is present, how do modules interact with eachother, what recovery systems are in place. Just like design patterns, there are architectural patterns: MVC, 3-tier layered design, etc.

Software design is about designing the individual modules / components. What are the responsibilities, functions, of module x? Of class Y? What can it do, and what not? What design patterns can be used?

So in short, Software architecture is more about the design of the entire system, while software design emphasizes on module / component / class level.

Answer 3

Software architecture is best used at the system level, when you need to project business and functions identify by higher architecture levels into applications.

For instance, your business is about "Profit and Loss" for traders, and your main functions involved "portfolio evaluation" and "risk computation".

But when a Software Architect will details his solution, he will realize that:

"portfolio evaluation" can not be just one application. It needs to be refined in manageable projects like:

• GUI
• Launcher
• Dispatcher
• ...

(because the operations involved are so huge they need to be split between several computers, while still being monitored at all times through a common GUI)

a Software design will examine the different applications, their technical relationship and their internal sub-components.
It will produce the specifications needed for the last Architecture layer (the "Technical Architecture") to work on (in term of technical framework or transversal components), and for the project teams (more oriented on the implementation of the business functions) to begin their respective projects.