Monday, October 09, 2006

Different aspects of software design

Yesterday while talking about goals of software design with some learning participants, we had an interesting discussion about the various aspects of software design. It is analogous to designing a housing complex. There is the macro level design of the buildings, gardens, club house, and jogging track. Then within every building we design the floor plan and the elevation. Each apartment has it's interiors designed separately. Beyond these designs, we also design the electrical systems, drainage systems, etc. The purpose of each design is different.

Similarly in an enterprise software system, we have various aspects of design. Some of them are:

  1. Enterprise and deployment design
  2. Component design
  3. Class design
  4. User Interface design

Each of these deals with a different aspect of the software system and has different goals.

Enterprise design  addresses high level components like naming and directory servers, application server, messaging server, databases, clusters, high level components and their deployment. The purpose of enterprise and deployment design is to create a deployment that fulfills the performance, budget, connectivity, and scalability needs of the enterprise. An enterprise designed must understand the capability of application servers, databases, clusters and other services such as naming and directory services. He must be able to balance requirement with capabilities and costs. An enterprise designer needs to figure out which components get deployed on which servers and how they interact with each other.

Component design usually addresses using and creating reusable components. While creating a software system, we often have to make build vs. buy decisions for certain reusable components. If we come across functionality that we feel can be reused across projects, then we factor out that functionality into a separate component. Each component should ideally have clear responsibilities which should be represented by the public interface of a facade class. This facade class will serve as the point of interaction for the rest of the software system.

Class design deals with flexibility, extensibility, and maintainability. It is all about identifying classes, assigning responsibilities, and understanding how the classes will interact with each other to fulfill their responsibilities. Here is where we deal with concepts like loose coupling, inheritance, polymorphism, and software design patterns. To learn more about object oriented class design, you can refer to the free (under development) course on object oriented analysis and design hosted on our site.

User Interface design addresses usability issues of a software system. Through usability design we ensure that the user interface is intuitive and easy to use. It should be easy and quick to do common tasks, and impossible to do things the user is not allowed to do. It should present information in a way that is easy to use.

All of these are various aspects of software design. Each has a specific goal and a process to achieve good design. 

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