1Lecture 8 Introduction to Systems Analysis l Objectives –Explain how systems analysis relates to business needs, problems, and opportunities –List and describe the types of system requirements that must be identified during systems analysis –Describe the symbols used in data flow diagrams and explain the rules for their use –Explain the sequence of data flow diagrams, from general to specific, and what each data flow contains –Draw a complete set of data flow diagrams for an information system

2Lecture 8 l Objectives of Systems Analysis –Learn how the current system works –Determine and document fully how the system could work better –Develop a logical model of the new system –Make recommendations to management Introduction

3Lecture 8 Overview of the Systems Analysis l Systems analysis phase tasks –Gather and record facts about the current system and what is required to support business needs l Three-step approach to decision-making –Determine the facts –Analyze the facts –Make a decision l Two steps in the systems analysis phase –Requirements determination (fact-finding) –Requirements analysis

4Lecture 8 The Challenge of Systems Analysis l Requirements determination questions –Who does it? –What is done? –Where is it done? –When is it done –How is it done l Another important question –Why?

5Lecture 8 Fact-finding Techniques l Interviewing l Documentation review l Observation l Questionnaires l Sampling l Research

6Lecture 8 The Challenge of Systems Analysis l Requirements analysis questions –Who should do it? –What should be done? –Where should it be done? –When should it be done? –How should it be done?

7Lecture 8 Systems Requirements l Characteristics or features that must be included to satisfy business requirements –Outputs –Inputs –Processes –Timing –Controls –Volumes. sizes, and frequencies

8Lecture 8 Structured Analysis l Examines inputs, outputs, and processes l Uses three main tools –Data flow diagrams (DFDs) –Data dictionary –Process descriptions l Tools can be applied using computer- aided software engineering (CASE) tools

9Lecture 8 Data Flow Diagrams l Data flow diagrams (DFDs) are graphical aids that describe an information system l DFDs represent a logical model that shows what a system does, not how it does it

10Lecture 8 Data Flow Diagrams l Data flow diagram symbols –Four basic symbols l Process l Data flow l Data store l External entity

11Lecture 8

12Lecture 8 Data Flow Diagrams –Process symbol l Symbol is a rectangle with rounded corners l Documented with process descriptions l Receive input data and produces output l Output has a different form, or content, or both l Details are shown in a process description l In DFDs the process symbol appears as a black box, underlying details not shown

13Lecture 8 Data Flow Diagrams –Data flow symbol l Symbol is a line with an arrowhead showing direction l A path for data to move from one part of the system to another l Might represent one or many pieces of data l At least one data flow must enter and exit each process

14Lecture 8

15Lecture 8 Data Flow Diagrams –Data flow symbol l Incorrect process and data flow combinations cause problems àSpontaneous generation (miracle) àBlack hole àGray hole

16Lecture 8

17Lecture 8 Data Flow Diagrams –Data store symbol l Symbol is a rectangle open on the right side l Data store also is called a data repository l Represents data that is retained for later processing l Must be connected to a process with a data flow l Must have at least one outgoing and incoming data flow

18Lecture 8

19Lecture 8

20Lecture 8 Data Flow Diagrams –External entity symbol l Symbol is a square, usually shaded l Represents a person, organization, or other system that provides data or receives output from the system l External entities are called terminators àSource (supplies data to the system) àSink (receives data from the system)

21Lecture 8

22Lecture 8

23Lecture 8 Data Flow Diagrams l Context diagrams –Top-level view that shows the overall boundaries of the system –Represent the results of fact-finding –One process symbol, numbered 0 (zero) is drawn in the center –Data flows connect the process to the entities –Abbreviated symbols can be used to identify entities

24Lecture 8

25Lecture 8

26Lecture 8 Data Flow Diagrams l Conventions for data flow diagrams –Each context diagram must fit on one page –Process name in the context diagram should be the name of the information system –Use unique names within each set of symbols –Do not cross lines –Use abbreviated identifications –Use a unique reference number for each process symbol

27Lecture 8

28Lecture 8 Data Flow Diagrams l Lower-level diagrams –Usually necessary to show more detail –Design must consider l Leveling l Balancing l Data stores

29Lecture 8 Data Flow Diagrams –Leveling l Process of drawing increasingly detailed diagrams l Also called exploding, partitioning, or decomposing –Balancing l Maintains consistency among an entire set of DFDs l Parent’s input and output data flows are preserved on the child –Data stores l Might not appear on higher-level DFDs l Are shown on the the highest-level DFD that has two or more processes using that data store

30Lecture 8

31Lecture 8

32Lecture 8