1 BTEC HNC Systems Support Castle College 2007/8 Systems Analysis Lecture 9 Introduction to Design

2 BTEC HNC Systems Support Castle College 2007/8 Lecture Objectives The transition to design Design Guidelines Design Trade-offs Prototypes Design Modelling Tools Process Flowcharts & Data Flow Models

3 BTEC HNC Systems Support Castle College 2007/8 Transition to Design If management decide to develop the system in-house then the transition to the system Design phase begins This phase uses systems design guidelines It sometimes requires prototyping methods and tools System Requirements Specification / Document is key Logical and Physical Designs

4 BTEC HNC Systems Support Castle College 2007/8 Design Guidelines The systems analyst must understand the logical design of a system before beginning the physical design First step is to revue the system requirements document The actual design process can then begin

5 BTEC HNC Systems Support Castle College 2007/8 Steps in Design Phase

6 BTEC HNC Systems Support Castle College 2007/8 Stages and Steps The systems design stage is not a series of clearly defined steps Many system components are interdependent Sometimes changes to one thing can cause a knock on effect to other areas of design

7 BTEC HNC Systems Support Castle College 2007/8 System Design Objectives To satisfy the defined requirements and constraints Must be accepted by the user Must support the organisation’s business objectives Must do what it was meant to do

8 BTEC HNC Systems Support Castle College 2007/8 System Design Objectives The system must be reliable in order to adequately handle errors, hardware failures and human mistakes A good system will plan for errors, detect them as soon as possible and allow for their correction without damaging the system itself Must be stable and resilient

9 BTEC HNC Systems Support Castle College 2007/8 System Design Objectives The system must be maintainable Should be well designed and flexible Allow for future modifications Clearly and accurately documented

10 BTEC HNC Systems Support Castle College 2007/8 System Design Considerations

11 BTEC HNC Systems Support Castle College 2007/8 Activity As the previous slide demonstrates design considerations should include the following: –users –data –Architecture Consider what is meant by this… (Steps Slide)

12 BTEC HNC Systems Support Castle College 2007/8 Logical Design Logical design defines the functions and features of the system (What) –Inputs –Outputs –Processes This does not take into account how the tasks will be accomplished physically (How)

13 BTEC HNC Systems Support Castle College 2007/8 Logical and Physical Design Physical design is the actual blueprint of the system describing the construction of the system It is built upon the logical design specification It is concerned with how the system will meet the requirements

14 BTEC HNC Systems Support Castle College 2007/8 Physical Design “In a typical system the physical design will describe the actual processes of entering, verifying and storing data. The physical layout of data files Sorting procedures, format of reports etc”. p222 shelley cashman et al

15 BTEC HNC Systems Support Castle College 2007/8 Data Design (NB) Data design defines the Physical data structures Elements Relationships NOTE: Data design and user interface will influence each other; could be data design driven

16 BTEC HNC Systems Support Castle College 2007/8 Data Considerations Delays cause Data Errors therefore: Data should be entered when it occurs It should be verified immediately to catch any errors Automated data entry should be used whenever possible

17 BTEC HNC Systems Support Castle College 2007/8 More Data Error Guidelines Data should be entered into the system only once as data duplication should be avoided Every instance of entry and change to the data should be logged Changes to critical values should be reported to trace the changes (audit facility)

18 BTEC HNC Systems Support Castle College 2007/8 User Considerations Design of the system should include consideration of how the system will affect the user – points to remember 1.Input processes should be easy to follow and forgiving of errors 2.Output should be attractive and easy to understand – with an appropriate level of detail

19 BTEC HNC Systems Support Castle College 2007/8 User Interface Guidelines Focus on business objectives Build an interface that is easy to learn and use Provide features that promote efficiency Make it easy for users to correct errors

20 BTEC HNC Systems Support Castle College 2007/8 User Interface Guidelines Minimise input data problems Provide feedback to users Create an attractive layout and design Use familiar terms and images (More in Lecture 10)

21 BTEC HNC Systems Support Castle College 2007/8 Software Architecture Considerations Consider the design of the architecture Modular design creates individual processing components (modules) which then connect to a higher level program Single function design modules are easy to understand, implement and maintain

22 BTEC HNC Systems Support Castle College 2007/8 Component Architecture Considerations Requirements and Constraints regarding physical system architecture (e.g. server/workstation locations, networking, etc) Physical location of components, and their interaction Backup/Recovery Security considerations

23 BTEC HNC Systems Support Castle College 2007/8 Design Trade-offs “Design goals often conflict with each other. In the system design phase you must constantly analyse alternatives and weigh trade offs” (Shelley Cashman et al) Programming requirements might be more complex to make a system easier to use. Making the system more flexible may make maintenance more difficult

24 BTEC HNC Systems Support Castle College 2007/8 Using Prototypes in Design “Prototyping produces an early, rapidly constructed working version of the proposed information system. It is a common technique which can be used to design anything from a new home to a computer network” – Shelly Cashman et al p228 Ref: Tutorial 4

25 BTEC HNC Systems Support Castle College 2007/8 Other Modelling Tools Process Flowcharts Data flow models Object modelling tools CASE tools System flowcharts Activity Diagrams (more detailed) Sequence Diagrams etc

26 BTEC HNC Systems Support Castle College 2007/8 System Flowcharts Another method of describing the physical design of a system Definition: “A system flowchart is a tool that uses various symbols to identify input, output processes and files”

27 BTEC HNC Systems Support Castle College 2007/8 American National Standards Institute (ANSI) Symbols Display Library / Pre-defined Program Decision Manual Input

28 BTEC HNC Systems Support Castle College 2007/8 Flowchart using ANSI standard Shelly et al Fig 5.32

29 BTEC HNC Systems Support Castle College 2007/8 Data Flow Diagrams Process Data Flow Real-time Link External Agent Data Store

30 BTEC HNC Systems Support Castle College 2007/8 External agent, data flows, and the process come from information about the event in the event table: 1 Look up item availability Catalogue Product Item Inventory Item Data stores come from Entity- relationship diagram Customer Item inquiry Item availability details SourceTriggerActivity Destination Response

31 BTEC HNC Systems Support Castle College 2007/8 In Conclusion The transition to design Design Guidelines Design Trade-offs Prototypes Design Modelling Tools Process Flowcharts & Data Flow Models