Software design
- 1. DESIGN CONCEPTS & PRINCIPLES SAVYASACHI SHARMA MUZAFFARPUR INSTITUTE OF TECHNOLOGY Muzaffarpur4/11/2020 1
- 2. DESIGN - Definition • The process of applying various techniques and principles for the purpose of defining a device, a process or a system in sufficient detail to permit its physical realization. • It is an architectural representation, a format, a guideline represented as symbols, notations, pictorial forms, that guides us how construct/ develop a product/process/system most economically, efficiently and effectively, that reduces the risk of failures. • Design is the highly creative phase in the software development where the designer plans how a software system should be produced in order to make it functional, reliable and reasonably easy to understand, modify and maintain.4/11/2020 2
- 3. • The goal of the design phase is to take the SRS document as input and to produce the output as a design document leading to final product. • System design is the representation of an object being created. • A system must be designed in such a way that it meets the performance requirements. • The designer’s goal is to produce a model of an entity that will later be built. • Software design changes continually. • Importance of s/w design is stated with a Quality • Design is the place where quality is fostered in s/w development 4/11/2020 3
- 4. • Design provides us with representations of s/w that can be assessed for quality. • Design is the only way that we can accurately translate requirements into finished s/w product. • Serves as foundation for s/w engineering and s/w maintenance steps. • Without design we risk building an unstable product – one that will fail when small changes are made, one that is difficult to test, one whose quality can not be assessed. 4/11/2020 4
- 5. Data Dictionary DFD STD ERD CSPEC PSPEC DATA DESIGN ARCHITECTURAL DESIGN INTERFACE DESIGN PROCEDURAL DESIGN Translating the Analysis Model into a S/W Desgn 4/11/2020 5
- 6. Designing the software System • Data design: transforms the information domain into data structures. (ERD/DD) • Architectural Design: defines relationship among major structural elements of program. It is modular framework of a computer program derived from interaction of sub-systems • Interface design: describes how the software interacts within itself, to systems that interoperates with it, and with humans who use it. An interface implies a flow of information (data/control) (DFD/CFD) • Procedural design: transforms structural elements of the program architecture into a procedural description of software components. (PSPEC,CSPEC,STD) 4/11/2020 6
- 7. General tasks involved in design process • Design the overall system process • Segment the system into modules • Design the database • Specify details of program • Design input and output • Design controls of the system • Document the system design • System reviews 4/11/2020 7
- 8. Design Objectives • Correct • Complete • Reduction of complexities • Understandable • Modular construction • Maintainable • Risk mitigation • Optimal utilisation of resources • Better scheduling • Meeting the schedules and deadlines 4/11/2020 8
- 9. Design Goals • To rationalise and streamline or simplify processing • To extend processing capability and flexibility • To increase productivity by reducing redundant activities and eliminating unnecessary activities • To increase management visibility • Better control over operating processes • To facilitate managerial planning and analysis of business activities. 4/11/2020 9
- 10. Design Constraints • Budget • Time • Customer • Attitude of the user • Technical people / skill • Standards • Hardware and software platforms • Integration with other systems 4/11/2020 10
- 11. Design and s/w Quality • S/W design is assessed with a series of FTR and walkthroughs. • McGlaughlin suggests 3 characteristics that serve as a guide for the evaluation of a good s/w design. • The design must implement all the explicit requirements contained in the analysis model, and it must accommodate all of the implicit requirements desired by the customer. • The design must be readable, understandable guide for those who generate code and for those who test and subsequently maintain the s/w. • The design must provide a complete pictures of the software, addressing the data, functional, and behavioural domains from implementation perspective4/11/2020 11
- 12. Technical criteria for good design • Hierarchical organisation • Modular construction • Functional • Efficient • Response times • Flexible • Portable • Reliable • Economical • Both data and procedural abstractions • Should lead to modules (subroutines/procedures) • Should lead to interfaces • Reduced complexity of connections b/w modules • Should be derived using a repeatable method • Secure • Usable4/11/2020 12