Systems Analysis & Design

Transcription

1 Systems Analysis & Design Dr. Ahmed Lawgali Slide 1

2 Systems Analysis & Design Course Textbook: Systems Analysis and Design With UML 2.0 An Object-Oriented Approach, Second Edition Introduction to Systems Analysis and Design PowerPoint Presentation for Alan Dennis, Barbara Wixom, and David Tegarden 2005 John Wiley & Sons, Inc. Slide 2

3 Key Ideas Many failed systems were abandoned because analysts tried to build wonderful systems without understanding the organization. The primarily goal is to create value for the organization. Quality is satisfaction of requirements, not goodness Slide 3

4 Key Ideas The systems analyst is a key person analyzing the business, identifying opportunities for improvement, and designing information systems to implement these ideas. It is important to understand and develop through practice the skills needed to successfully design and implement new information systems. Slide 4

5 Slide 5

6 THE SYSTEMS DEVELOPMENT LIFE CYCLE (SDLC) The systems development life cycle (SDLC) is the process of understanding how an information system (IS) can support business needs by designing a system, building it, and delivering it to users. Slide 6

7 Major Attributes of the Lifecycle The project Moves systematically through phases where each phase has a standard set of outputs Produces project deliverables Uses deliverables in implementation Results in actual information system Uses gradual refinement Slide 7

8 4 Main Project Phases Planning Why build the system? Analysis What, when, where will the system be? Design How will the system work? Implementation System construction & delivery Slide 8

9 Planning Identifying business value (is it worth doing?) Analyze feasibility (is it possible?) Develop work plan (when?) Staff the project (who?) Control and direct project Slide 9

10 Analysis Analysis (what do we want? Who will use the system?) Information gathering Process modelling (what happens?) Data modelling and to what? Slide 10

11 Design Design strategy Architectural design Interface design (HCI) Database and file design Program design (what will the programs do?) Slide 11

12 Implementation Construction (Programming, testing, validation etc) Installation (including migration, change management) Slide 12

13 Processes and Deliverables Process Product Planning Project Plan Analysis System Proposal Design Implementation System Specification New System and Maintenance Plan Slide 13

14 Slide 14

15 What Is a Methodology? A formalized approach or series of steps Writing code without a well-thought-out system request may work for small programs, but rarely works for large ones. Slide 15

16 System Development Methodologies Structured Design Rapid Application Development Agile Development Slide 16

17 1. STRUCTURED DESIGN Projects move methodically from one to the next step Generally, a step is finished before the next one begins Slide 17

18 Waterfall Development Method With waterfall development based methodologies, the analysts and users proceed in sequence from one phase to the next. Slide 18

19 Waterfall Development Method The key deliverables for each phase are typically very long (often hundreds of pages in length) and are presented to the project sponsor for approval as the project moves from phase to phase. Once the sponsor approves the work that was conducted for a phase, the phase ends and the next one begins. Slide 19

20 Waterfall Development Method Slide 20

21 Pros and Cons of the Waterfall Method Pros Identifies systems requirements long before programming begins Cons Design must be specified on paper before programming begins Long time between system proposal and delivery of new system Slide 21

22 Parallel Development Parallel development methodology attempts to address the problem of long delays between the analysis phase and the delivery of the system. Slide 22

23 Parallel Development Instead of doing design and implementation in sequence, it performs a general design for the whole system and then divides the project into a series of distinct subprojects that can be designed and implemented in parallel. Once all subprojects are complete, the separate pieces are integrated and the system is delivered Slide 23

24 Parallel Development Slide 24

25 Parallel Development The approach still suffers from problems caused by paper documents. It also adds a new problem: Sometimes the subprojects are not completely independent; design decisions made in one subproject can affect another, and the end of the project can require significant integration efforts. Slide 25

26 2. RAPID APPLICATION DEVELOPMENT (RAD) RAD-based methodologies attempt to address both weaknesses of structured design methodologies by adjusting the SDLC phases to get some part of the system developed quickly and into the hands of the users. In this way, the users can better understand the system and suggest revisions that bring the system closer to what is needed Slide 26

27 2. RAPID APPLICATION DEVELOPMENT (RAD) Most RAD-based methodologies recommend that analysts use special techniques and computer tools to speed up the analysis, design, and implementation phases, such as computer-aided software engineering (CASE) tools, joint application design (JAD) sessions, fourth-generation or visual programming languages Slide 27

28 Rapid Application Development Categories Phased development a series of versions, later combined Prototyping System prototyping Throw-away prototyping Design prototyping Slide 28

29 Phased Development A phased development-based methodology breaks an overall system into a series of versions that are developed sequentially. The analysis phase identifies the overall system concept, and the project team, users, and system sponsor then categorize the requirements into a series of versions. Slide 29

30 Phased Development Slide 30

31 Phased Development The major drawback to phased development is that users begin to work with systems that are intentionally incomplete. It is critical to identify the most important and useful features and include them in the first version and to manage users expectations along the way. Slide 31

32 Prototyping A prototyping-based methodology performs the analysis, design, and implementation phases concurrently, and all three phases are performed repeatedly in a cycle until the system is completed. Slide 32

33 How Prototyping Works Slide 33

34 Prototyping The key advantage of a prototyping-based methodology is that it very quickly provides a system with which the users can interact, even if it is not ready for widespread organizational use at first. Rather than attempting to understand a system specification on paper, the users can interact with the prototype to better understand what it can and cannot do. Slide 34

35 Prototyping The major problem with prototyping is that its fast-paced system releases challenge attempts to conduct careful, methodical analysis. Often the prototype undergoes such significant changes that many initial design decisions become poor ones. This can cause problems in the development of complex systems because fundamental issues and problems are not recognized until well into the development process. Slide 35

36 Throwaway Prototyping Throwaway prototyping-based methodologies are similar to prototyping-based methodologies in that they include the development of prototypes; however, throwaway prototypes are done at a different point in the SDLC. Slide 36

37 Throwaway Prototyping The throwaway prototyping based methodologies have a relatively thorough analysis phase that is used to gather information and to develop ideas for the system concept. However, users might not completely understand many of the features they suggest, and there may be challenging technical issues to be solved. Each of these issues is examined by analyzing, designing, and building a design prototype. Slide 37

38 Throwaway Prototyping Slide 38

39 Throwaway Prototyping A design prototype is not a working system; it is a product that represents a part of the system that needs additional refinement, and it contains only enough detail to enable users to understand the issues under consideration. Slide 39

40 Throwaway Prototyping It can take longer to deliver the final system as compared to prototyping-based methodologies (because the prototypes do not become the final system), but this type of methodology usually produces more stable and reliable systems. Slide 40

41 3. AGILE DEVELOPMENT Simple iterative application development One of the more popular examples of agile development methodology is : Extreme programming (XP) Slide 41

42 Extreme Programming (XP) Extreme programming (XP) is founded on four core values: communication, simplicity, feedback, and courage. Three of the key principles that XP uses to create successful systems are: continuous testing, simple coding performed by pairs of developers, close interactions with end users to build systems very quickly. Slide 42

43 Extreme Programming (XP) Slide 43

44 Extreme Programming (XP) An XP project begins with user stories that describe what the system needs to do. Then, programmers code in small, simple modules and test to meet those needs. Users are required to be available to clear up questions and issues as they arise. Slide 44

45 Selecting the Appropriate Methodology Clarity of User Requirements Familiarity with the Technology System Complexity System Reliability Length of Time Schedules Time Schedule Visibility Slide 45

46 Criteria for Selecting a Methodology Slide 46

47 Slide 47

48 Project Team Roles Business analyst (business value) Systems analyst (IS issues) Infrastructure analyst (technical issues how the system will interact with the organization s hardware, software, networks, databases) Change management analyst (people and management issues) Project manager (budget, time, planning, managing) Slide 48

49 Summary The Systems Development Life Cycle (SDLC) consists of four stages: Planning, Analysis, Design, and Implementation The Major Development Methodologies: Structured Design Waterfall Method Parallel Development Rapid Application Development (RAD) Phased Development Prototyping (system prototyping) Throwaway Prototyping (design prototyping) Agile development extreme Programming Project Team Roles Slide 49

50 Summary -- Part 2 There are five major team roles: business analyst systems analyst infrastructure analyst change management analyst project manager. Slide 50