Structured system analysis

Structured System Analysis

•Modeling System Function•Data Flow Diagram•System Flowchart

•Modeling Stored DataEntity-RelationshipData Dictionary

Structured Analysis

• Throughout the phases of analysis anddesign, the analyst should proceed step bystep, obtaining feedback from users andanalyzing the design for omissions anderrors.

• Moving too quickly to the next phase mayrequire the analyst to rework portions of thedesign that were produced earlier.

Structured Analysis

• They Structured a project into small, well-definesactivities and specify the sequence and interactionof these activities.

• They use diagrammatic and other modelingtechniques to give a more precise (structured)definition that is understandable by both users anddevelopers.

• Structured analysis provides a clearrequirements statements that everyone canunderstand and is a firm foundation forsubsequent design and implementation.

• Part of the problem with systems analystsjust asking ‘the right questions’ that it isoften difficult for a technical person todescribe the system concepts back to the usercan understand.

Structured Analysis

• Structured methods generally include the use ofeasily understood, non technical diagrammatictechniques.

• It is important that these diagram do not containcomputer jargon and technical detail that the userwont understand – and does not needunderstand.

Structured Analysis

Why do we use these tools?

•Use graphics whenever possible to helpcommunicate better with the user.

•Differentiate between logical and physicalsystem

•Build a logical system model to familiarize theuser with system characteristics andinterrelationships before implementation.

Structured Analysis

• Data Flow Diagram (DFD)

• System Flowchart

•A Data Flow Diagram (DFD) is a graphical

representation of the "flow" of data through

an information system.

•It differs from the system flowchart as it shows the

flow of data through processes instead of computer

hardware.

•Data flow diagrams were invented by Larry

Constantine, developer of structured design, based

on Martin and Estrin's "data flow graph" model of

computation.

•It is common practice to draw a System Context

Diagram first which shows the interaction between

the system and outside entities.

•The DFD is designed to show how a system is

divided into smaller portions and to highlight the

flow of data between those parts.

•This context-level Data flow diagram is then

"exploded" to show more detail of the system being

modeled.

PASSENGER

AIRLINE

RESERVATION

SYSTEM

AIRLINE

TRAVEL AGENT

Travel Request

Preference and Available Flights

Ticketing Information

Passenger Reservation

0

Context –level flow diagram for an airline

reservation system

•A concrete, physical model that

documents, in an easily visualized,

graphical form, the system’s

discrete physical components (its

programs, procedures, files,

reports, screens, etc.).

•A system flowchart is a valuable presentation aid

because it shows how the system’s major components

fit together and interact.

• In effect, it serves as a system roadmap. During the

information gathering stage, a system flowchart is an

excellent tool for summarizing a great deal of technical

information about the existing system.

• A system flowchart can also be used to map a

hardware system.

•System flowcharts are valuable as project planningand project management aids.

•Using the system flowchart as a guide, discreteunits of work (such as writing a program orinstalling a new printer) can be identified, costestimated, and scheduled.

• On large projects, the components suggest howthe work might be divided into subsystems.

Flowcharting Symbols and Conventions

Sample Flowchart using predefined process

Sample Flowchart showing the predefined process

Shows one physical alternative

for implementing an inventory

system.

At the top left, a Sales receipt is

prepared as output from the Sell

appliance predefined process.

The data from the Sales

receipt are then input to

the Inventory program.

Subsequently, a printed Cash

flow report goes to the Financial

system.

Below the symbols that represent the system files are procedures to send advertising to customers, perform a physical inventory, process incoming shipments from suppliers, and reorder stock.

Except for the predefined processes, each symbol represents one of the system’s discrete components at a black-box level.

• Predefined process —On a systemflowchart, a high-level process that ismore fully documented in a separate,lower-level flowchart.

• System flowchart —A tool fordocumenting a physical system in whicheach component is represented by asymbol that visually suggests itsfunction.

• Entity-Relationship Diagram

• Data Dictionary

• An entity-relationship model is a systematic way ofdescribing and defining a business process.

• The process is modeled as components (entities) thatare linked with each other by relationships that expressthe dependencies and requirements between them,such as: one building may be divided into zero or moreapartments, but one apartment can only be located inone building.

• Entities may have various properties (attributes) thatcharacterize them. Diagrams created to represent theseentities, attributes, and relationships graphically arecalled entity–relationship diagrams.

• The elements that make up an organizational

system can be referred to as entities.

• An Entity may be a person, a place, or a thing,

such as a passenger on an airplane, a

destination, or a plane.

• Alternatively that entity may be an event, such

as the end of the month, a sales period, or a

machine breakdown.

• A relationship is the association that describes

the interaction among entities.

EMPLOYEE

PHONE EXTENSION

is listedfor

is assignedto

EMPLOYEE

DEPARTMENT

is a member of

contains

Relationships are normally given names that are verbs, while attributes and entities arenamed after nouns. This convention makes it easy to express relationships.

For example, if we name our Person/City relationship "Lives In", we can string them togetherto say "A person lives in a city."

We express relationships in E-R diagrams by drawing a line between the related entities andplacing a diamond shape that contains the relationship name in the middle of the line.

Here's how our Person/City relationship would look:

•A structured place to keep details of

the contents of data flows,

processes, and data store.

•It is a structured repository of data

about data.

•It is a set of definitions of all DFD

elements

•Documentation- it is a valuable referencein any organization.

•It improves analyst/user communicationby establishing consistent definitions ofvarious elements, terms and procedures

•It is important step in building a database