Introduction to Software Engineering/Architecture/Design

Software Design

The result of the software requirements analysis (SRA) usually is a specification. The design helps us turning this specification into a working system. As we have seen there are different kinds of software designs, the IEEE Std 610.12-1990 Standard Glossary of Software Engineering Terminology^[1] defines the following distinctions:

• Architectural Design: the process of defining a collection of hardware and software components and their interfaces to establish the framework for the development of a computer system.
• Detailed Design: the process of refining and expanding the preliminary design of a system or component to the extent that the design is sufficiently complete to begin implementation.
• Functional Design: the process of defining the working relationships among the components of a system.
• Preliminary Design: the process of analyzing design alternatives and defining the architecture, components, interfaces, and timing/sizing estimates for a system or components.

Hence software design includes architectural views, but also low-level component and algorithm implementation issues. Depending on the type, a software design may be platform-independent or platform-specific.

Design Considerations

There are many aspects to consider in the design of a piece of software. The importance of each should reflect the goals the software is trying to achieve. 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.
• Fault-tolerance - The software is resistant to and able to recover from component failure.
• Maintainability - The software can be restored to a specified condition within a specified period of time. For example, antivirus software may include the ability to periodically receive virus definition updates in order to maintain the software's effectiveness.
• Modularity - the resulting software comprises well defined, independent components. That 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.
• Packaging - Printed material such as the box and manuals should match the style designated for the target market and should enhance usability. All compatibility information should be visible on the outside of the package. All components required for use should be included in the package or specified as a requirement on the outside of the package.
• Reliability - The software is able to perform a required function under stated conditions for a specified period of time.
• Reusability - the software is able to add further features and modification with slight or no modification.
• Robustness - The software is able to operate under stress or tolerate unpredictable or invalid input. For example, it can be designed with a resilience to low memory conditions.
• Security - The software is able to withstand 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.

Modeling Language

Designers are assisted be the existence of modeling languages. They can be used to express information, knowledge or systems in a structure that is defined by a consistent set of rules. A modeling language can be graphical or textual. Examples of graphical modelling languages for software design are:

• Unified Modeling Language (UML) is a general modeling language to describe software both structurally and behaviorally. It has a graphical notation and allows for extension with a Profile (UML).
• Flowchart is a schematic representation of an algorithm or a stepwise process,
• Business Process Modeling Notation (BPMN) is an example of a Process Modeling language.
• Systems Modeling Language (SysML) is a new general-purpose modeling language for systems engineering.

There is quite a few more, but we will concentrate mostly on the UML as we will see in the next chapter.

References

2. Software Engineering[8th edition]-lan Sommerville publisher- Pearson

External Links

• IEEE Std 1016-1998 IEEE Recommended Practice for Software Design Descriptions
• A Software Design Specification Template