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
• 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
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 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
Systems Analysis and Design: Phase 2
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 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
Systems Analysis and Design: Phase 2
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
Systems Analysis and Design: Phase 2
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
Systems Analysis and Design: Phase 2
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
Systems Analysis and Design: Phase 2
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
Systems Analysis and Design: Phase 2
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
Look at balancing of Data
Flows between the two
diagrams
Systems Analysis and Design: Phase 2
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
Systems Analysis and Design: Phase 2
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
Look at balancing of Data
Flows between the two
diagrams
Explosion of
FILL ORDER
Process
Systems Analysis and Design: Phase 2
Level 1 Diagram
Level 0 Diagram
Explosion of
APPLY PAYMENT
Process
Look at balancing of Data
Flows between the two
diagrams
Systems Analysis and Design: Phase 2
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 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 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 Diagrams
Conventions for Data-Flow Diagram (contd..)
• Use abbreviated identification for external entities and dataflows. 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 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
Systems Analysis and Design: Phase 2
Mistakes in Data Flow Diagrams
Systems Analysis and Design: Phase 2
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