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PHASE 2: SYSTEMS ANALYSIS. Introduction At the beginning of the systems analysis phase, the systems analyst gathered information about the existing system using various techniques such as interview, questionnaire, observation, product sampling or JAD session

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phase 2 systems analysis
PHASE 2: SYSTEMS ANALYSIS

Introduction

  • At the beginning of the systems analysis phase, the systems analyst gathered information about the existing system using various techniques such as interview, questionnaire, observation, product sampling or JAD session
  • The analyst also gathered information regarding the need of the new system
  • The next activity is to understand the gathered information and develop a business model of the new system through process modeling

Systems Analysis and Design: Phase 2

process modeling
Process Modeling
  • A process model is a formal way of representing how a business system operates
  • It illustrates the processes or activities that are performed and data moves among them
  • Data flow diagrams are used to graphically represent the flow of data in a business system
  • It describes the processes that are involved in an information system to transfer data from the input to the file storage to the report generation

Systems Analysis and Design: Phase 2

data flow diagrams
Data Flow Diagrams

Logical and Physical Data Flow Diagrams

  • Data flow diagrams can be divided into logical and physical diagrams.
  • The logical data flow diagram describes flow of data through a system to perform certain functionality of a business.
  • The physical data flow diagram describes the implementation of the logical data flow through specific methods.

Systems Analysis and Design: Phase 2

data flow diagrams1
Data Flow Diagrams

Four basic symbols of a data-flow diagram

  • There are four basic symbols of a data flow diagram:
      • Process
      • Data Flow
      • Data Store
      • External Entity

Systems Analysis and Design: Phase 2

data flow diagram symbols
Data Flow Diagram Symbols

Systems Analysis and Design: Phase 2

data flow diagrams2
Data Flow Diagrams

Process Symbol

  • A process receives input data and produces output with a different content or form
  • Processes can be as simple as collecting input data and saving in the database, or it can be complex as producing a report containing monthly sales of all retail stores in the northwest region
  • The details of a process are not shown in the data flow diagram. They are documented separately in a process description in data dictionary.

Systems Analysis and Design: Phase 2

data flow diagrams3
Data Flow Diagrams

Data Flow Symbol

  • A data-flow is a path for data to move from one part of the information system to another.
  • A data-flow may represent a single data element such the Customer ID or it can represent a set of data element (or a data structure). Examples of data structure are: customer information (LastName, FirstName, SS#, Tel #, etc.) or order information (OrderId, Item#, OrderDate, CustomerID, etc.)
  • Because every process changes data from one form into another, at least one data-flow must enter and one data-flow must exit each process symbol

Systems Analysis and Design: Phase 2

data flow rules
Data Flow Rules

Systems Analysis and Design: Phase 2

data flow diagrams4
Data Flow Diagrams

Data Store Symbol

  • A data store or data repository is used to represent a situation when the system must retain data because one or more processes need to use the stored data in a later time
  • For example, transaction report of a customer bank account is printed at the end of a monthly cycle. Thus a record of each customer account transaction must be kept in the system.
  • A data store must be connected to a process with a data-flow:Each data store must have at least one input data-flow and at least one output data-flow (even if the output data-flow is a control or confirmation message).

Systems Analysis and Design: Phase 2

data store rules
Data Store Rules

Systems Analysis and Design: Phase 2

data flow diagrams5
Data Flow Diagrams

External Entity Symbol

  • An external entity is a person, department, outside organization, or other information system that provides data to the system or receives outputs from the system.
  • External entities are components outside of the boundaries of the information systems. They represent how the information system interacts with the outside world. (Compare this with an Entity in the E-R diagram.)
  • External entities also are called terminators because they are data origins or final destinations
  • An external entity must be connected to a process through a data-flow

Systems Analysis and Design: Phase 2

external entity rules
External Entity Rules

Systems Analysis and Design: Phase 2

data flow diagrams6
Data Flow Diagrams

Developing Data Flow Diagrams

  • Data flow diagrams are developed in a series of steps, starting with
    • a context diagram that represents the overall business system
    • The context diagram is then further exploded to a child diagram called level 0 diagram
    • The level 0 diagram is then exploded further to several child diagrams, called level 1 diagrams
    • The explosion of diagrams continues to level 2, 3, and so on until a business process is defined by a functional primitive that represents a single business function (add, delete, etc.)

Systems Analysis and Design: Phase 2

developing data flow diagrams
Developing Data Flow Diagrams

Systems Analysis and Design: Phase 2

data flow diagrams7
Data Flow Diagrams

Context Diagram

  • The context diagram is the highest level in a data flow diagram
  • It contains only one process (labeled 0) representing the entire business system
  • All external entities are shown on the context diagram as well as major data flow to and from them
  • The diagram does not contain any data storage

Systems Analysis and Design: Phase 2

context diagram
Context Diagram

Systems Analysis and Design: Phase 2

data flow diagrams8
Data Flow Diagrams

Level 0 Diagram

  • The context diagram is exploded into a level 0 diagram that contains all major processes of the business system
  • In addition to all external entities, major processes, and major data flows, it contains major data stores
  • Normally nine processes are included (to limit the number of processes in a page)
  • The processes are numbered as 1 through 9

Systems Analysis and Design: Phase 2

level 0 diagram

Context Diagram

Level 0 Diagram

Look at balancing of Data

Flows between the two

diagrams

Systems Analysis and Design: Phase 2

data flow diagrams9
Data Flow Diagrams

Another way of Creating Level 0 Diagram

  • First create DFD fragments from the Use Cases of the system – without including details of the processing
  • Then combine all DFD fragments to draw a 0-level diagram

Systems Analysis and Design: Phase 2

dfd fragment from a use case
DFD Fragment from a Use Case

Systems Analysis and Design: Phase 2

data flow diagrams10
Data Flow Diagrams

Level 1 Diagram

  • Each of the processes in the level 0 diagram is exploded further to include the detail functionality of the process
  • Thus there can be nine (9) level 1 diagrams
  • The processes are numbered as 1.1, 1.2, 1.3, …2.1, 2.2, 2.3, …3.1, 3.2, 3.3, … and so on

Systems Analysis and Design: Phase 2

level 1 diagram

Level 0 Diagram

Level 1 Diagram

Explosion of FILL ORDER Process

Look at balancing of Data

Flows between the two

diagrams

Systems Analysis and Design: Phase 2

level 1 diagram1

Level 0 Diagram

Level 1 Diagram

Explosion of

APPLY PAYMENT Process

Look at balancing of Data

Flows between the two

diagrams

Systems Analysis and Design: Phase 2

data flow diagrams11
Data Flow Diagrams

Data Flow Splits and Joins

  • A data flow split shows where a flow is broken into its component parts for use in separate processes
  • Data flow splits need not be mutually exclusive nor use all the data from the parent flow
  • As we move to lower levels we become more precise about the data flows
  • A data flow join shows where components are merged to describe a more comprehensive flow

Systems Analysis and Design: Phase 2

data flow diagrams12
Data Flow Diagrams

Conventions for Data-Flow Diagram

  • The context diagram must fit in one page
  • The process name in the context diagram should be the name of the information system.
    • For example, Grading System, Order Processing System, Registration System
  • Use unique names within each set of symbols
    • For example, there can be only one entity CUSTOMER in all levels of the data-flow diagrams. There can be only one process name CALCULATE OVERTIME among all levels of data-flow diagrams

Systems Analysis and Design: Phase 2

data flow diagrams13
Data Flow Diagrams

Conventions for Data-Flow Diagram (contd..)

  • On lower-level data-flow diagrams with multiple processes, one should not have more than nine (9) process symbols
  • Do not cross lines
    • One way to achieve this is to restrict the number of processes in a data-flow diagram
    • Another way to avoid crossing lines is to duplicate an external entity or data store. Use a special notation such as an asterisk, to denote the duplicate symbol

Systems Analysis and Design: Phase 2

data flow diagrams14
Data Flow Diagrams

Conventions for Data-Flow Diagram (contd..)

  • Use abbreviated identification for external entities and data-flows. For example, C for entity CUSTOMER, and D1 for data store STUDENT
  • Use a unique reference number for each process symbol
    • The process number in the context-level diagram is 0 (zero)
    • Other process numbers are in the hierarchy of (1, 2, 3,…); (1.1, 1.2, 1.3, …., 2.1, 2.2, 2.3,….); (1.1.1, 1.1.2, 1.1.3,…………………………………)

Systems Analysis and Design: Phase 2

data flow diagrams15
Data Flow Diagrams

Balancing and Leveling Data-Flow Diagrams

  • Balancing refers to the preservation of input and output data flows of the parent diagram on the child diagrams
  • Leveling means that the information system is first displayed as a single process, and then shows more detail in subsequent child diagrams until all processes become functional primitives

Systems Analysis and Design: Phase 2

balancing data flow diagrams
Balancing Data Flow Diagrams

Systems Analysis and Design: Phase 2

mistakes in data flow diagrams
Mistakes in Data Flow Diagrams

Systems Analysis and Design: Phase 2

class assignment
Class Assignment
  • Draw a 0-level Data Flow diagram of an online store to order some products which involves at least three processes, few external entities, few input and output data flows, few data stores to complete a business cycle.
  • You can use Microsoft Offcie Visio

Systems Analysis and Design: Phase 2