chapter 5 systemdesign2008.pptx for cimputer science students
- 1. Chapter 5 System Design Design is highly creative stage in software development. designer plans how the system or program should meet the customer’s needs how to make system effective and efficient. System design is the transformation of the analysis model into a system design model blueprint or a plan for a solution
- 2. Con’t…. Design is about the HOW the system will perform its functions provides the overall decomposition of the system allows to split the work among a team of developers also lays down the groundwork for achieving nonfunctional requirements (performance, maintainability, reusability, etc.) coming up with solution models taking the target implementation technology into account
- 3. cont… Software design provides a (traceability) link between requirements and an implementable specification. We have to used designing methodology or principles to define system design/ for physical realization. Designing methodology is systematic approach used to create a design by applying a set of techniques and guidelines.
- 4. Design process Study and understand the problem from different viewpoints Identify potential solutions and evaluate the tradeoffs Design experience, reusable artifacts, simplicity of solutions Sub-optimal, but familiar solutions often preferred -advantages/disadvantages well known Design is about making tradeoffs! Develop different models of system at different levels of abstraction and for different perspectives
- 5. Con’t…..
- 6. Software Design Levels Architectural design Structure system into components Define the interfaces between components Detailed design of each component Define internal logic Define internal data structures •High-level design Define file structures Logical database design
- 7. Challenges in Design Complexity Often arbitrary, dependent on designer rather than problem (“accidental complexity”) Conformity Often expected to conform to other software (e.g. legacy, standards) Changeability Needs to support change due changing requirements, constraints, etc. Invisibility No visible link from between design plans and product
- 8. Design Objectives/Properties Correctness: find the best possible design within the limitations Verifiability: how easily the correctness of the design can be checked Completeness: Include all the things (data structures, modules, external interfaces,) Traceability: the entire design element be traceable to the requirements. Efficiency: the proper use of scarce resources by the system Simplicity. Especially related to maintainability
- 9. User Interface Design System users often judge a system by its interface rather than its functionality A poorly designed interface can cause a user to make catastrophic errors and never be used Most users of business systems interact with these systems through graphical user interfaces (GUIs) In some cases, legacy text-based interfaces are still used
- 10. Cont’ GUI characteristics Characteristic Description Windows Multiple windows allow different information to be displayed simultaneously on the user’s screen. Icons Icons different types of information.On some systems, icons represent files; on others, icons represent processes. Menus Commands are selected from a menu rather than typed in a command language. Pointing A pointing device such as a mouse is used for selecting choices from a menu or indicating items of interest in a window. Graphics Graphical elements can be mixed with text on the same display.
- 11. GUI advantages They are easy to learn and use. Users without experience can learn to use the system quickly. The user may switch quickly from one task to another and can interact with several different applications. Information remains visible in its own window when attention is switched. Fast, full-screen interaction is possible with immediate access to anywhere on the screen
- 12. UI design principles User familiarity The interface should be based on user-oriented terms and concepts rather than computer concepts E.g., an office system should use concepts such as letters, documents, folders etc. rather than directories, file identifiers, etc. Consistency The system should display an appropriate level of consistency Commands and menus should have the same format, command punctuation should be similar, etc. Minimal surprise If a command operates in a known way, the user should be able to predict the operation of comparable commands
- 13. Cont…. Recoverability The system should provide some resilience to user errors and allow the user to recover from errors This might include an undo facility, confirmation of destructive actions, 'soft' deletes, etc. User guidance Some user guidance such as help systems, on-line manuals, etc. should be supplied User diversity Interaction facilities for different types of user should be supported E.g., some users have seeing difficulties and so larger text should be available
- 14. User-system interaction How the user interacts with the system ? Direct manipulation Easiest to grasp with immediate feedback Difficult to program Menu selection User effort and errors minimized Large numbers and combinations of choices a problem Form fill-in Ease of use, simple data entry Tedious, takes a lot of screen space Command language Easy to program and process Difficult to master for casual users Natural language Great for casual users Tedious for expert users
- 15. Cont…. Information presentation Colour displays Error messages System and user-oriented error messages Generally UI design should be Attractive Simple to use Responsive in short time Clear to understand Consistent on all interfacing screens