desirable features and design issues

desirable features

There are many aspects to consider in the design of a piece of software. The importance of each consideration should reflect the goals and expectations that the software is being created to meet. Some of these aspects are:

• Compatibility - The software is able to operate with other products that are designed for interoperability with another product. For example, a piece of software may be backward-compatible with an older version of itself.
• Extensibility - New capabilities can be added to the software without major changes to the underlying architecture.
• Modularity - the resulting software comprises well defined, independent components which leads to better maintainability. The components could be then implemented and tested in isolation before being integrated to form a desired software system. This allows division of work in a software development project.
• Fault-tolerance - The software is resistant to and able to recover from component failure.
• Maintainability - A measure of how easily bug fixes or functional modifications can be accomplished. High maintainability can be the product of modularity and extensibility.
• Reliability (Software durability) - The software is able to perform a required function under stated conditions for a specified period of time.
• Reusability - The ability to use some or all of the aspects of the preexisting software in other projects with little to no modification.
• Robustness - The software is able to operate under stress or tolerate unpredictable or invalid input. For example, it can be designed with resilience to low memory conditions.
• Security - The software is able to withstand and resist hostile acts and influences.
• Usability - The software user interface must be usable for its target user/audience. Default values for the parameters must be chosen so that they are a good choice for the majority of the users.
• Performance - The software performs its tasks within a time-frame that is acceptable for the user, and does not require too much memory.
• Portability - The software should be usable across a number of different conditions and environments.
• Scalability - The software adapts well to increasing data or number of users.

design issues

The Problem of scale:    A fundamental problem of software engineering is the problem of scale; development of a very large system requires a very different set of methods compared to developing a small system. In other words, the methods that are used for developing small systems generally do not scale up to large systems. A different set of methods has to be used for developing large software. Any large project involves the use of technology and project management.

For software projects, by technology we mean the methods, procedures, and tools that are used. In small projects, informal methods for development and management can be used. However, for large projects, both have to be much more formal.

While dealing with a small software project, the technology requirement is low and the project management requirement is also low. However, when the scale changes to large systems, to solve such problems properly, it is essential that we move in both directions-the methods used for development need to be more formal, and the project management for the development project also needs to be more formal.

            Cost, schedule and quality: The cost of developing a system is the cost of the resources used for the system, which, in the case of software, are the manpower, hardware, software, and the other support resources. Generally, the manpower component is predominant, as software development is largely labor-intensive and the cost of the computing systems is now quite low.

Hence, the cost of software project is measured in terms of person-months, i.e. the cost is considered to be the total number of person-months spent in the project. Schedule is an important factor in many projects. Business trends are dictating that the time to market of a product should be reduced; that is, the cycle time from concept to delivery should be small. Any business with such a requirement will also require that the cycle time for building a software needed by the business be small.

One of the major factors driving any production discipline is quality. We can view quality of a software product as having three dimensions:

             Product Operation
             Product Transition
             Product Revision        

The Problem of consistency: Though high quality, low cost and small cycle time are the primary objectives of any project, for an organization there is another goal: consistency. An organization involved in software development does not just want low cost and high quality for a project, but it wants these consistently.