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 various techniques like Use Case and Process Modeling

Systems Analysis and Design: Phase 2

A process model is a formal way of representing how a business system operates

It illustrates the processes or activities that are performed and the data that 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 or database to the report generation


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.


Four basic symbols of a data-flow diagram

There are four basic symbols of a data flow diagram:

ProcessProcess Data FlowData Flow Data StoreData Store External EntityExternal Entity


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.


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


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).


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


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.)


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


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


Context DiagramContext Diagram


Look at balancing of Data Look at balancing of Data Flows between the two Flows between the two

diagramsdiagrams

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


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


Level 0 DiagramLevel 0 Diagram


Explosion of FILL ORDER Process


diagramsdiagrams

Level 0 DiagramLevel 0 Diagram


Explosion of

APPLY PAYMENT Process


diagramsdiagrams

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


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


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


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,…………………………………)


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


• Draw a 0-level Data Flow diagram of Draw a 0-level Data Flow diagram of an online store to order some an online store to order some products which involves at least products which involves at least three processes, few external three processes, few external entities, few input and output data entities, few input and output data flows, few data stores to complete a flows, few data stores to complete a business cycle.business cycle.

• You can use Microsoft Office VisioYou can use Microsoft Office Visio


PHASE 2: SYSTEMS ANALYSIS

Documents

Transcript of PHASE 2: SYSTEMS ANALYSIS