Module 3: Analysis

Yogesh Kumar

Asst. Prof.

SCSE

Contents

• Structured Analysis • Data Flow Analysis

• Features• Data Flow Diagrams (DFDs)• Data Dictionary

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Structured Analysis Development Strategy

• A SA is expected to perform many tasks like learn, develop, document, evaluate, recommend the system, etc.  (pg 151)

• In order to be successful, he structure the process they follow in developing new systems.

• Structured Analysis is a development method for the analysis of existing manual or automated system, leading to the development of specifications for a new or modified system.

• Structured Analysis allows the SA to learn about a system or process (activity) in a manageable  and a logical way while providing a basis for ensuring that important details are not overlooked.

• Structured Analysis means to organize task in Requirement Determination to provide an accurate and complete understanding of a current system.

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• Components of Structured Analysis• Graphic Symbols: 

• Icons and conventions for identifying and describing the components of a system and the relationship among these components.

• Data Dictionary:• Description of all data used in the system

• Procedure and Process Description• Formal statements using techniques and languages to describe important activities

• Rules• Standards for describing and documenting the system correctly and completely.

• Structured Analysis == Data flow analysis

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Data Flow Analysis

• SA want to know the answer to the following questions:• What processes make up a system?• What data are used in each process?• What data are stored?• What data enter and leave the system?

• Data flow analysis studies the flow/use of data in various activities like input, processing, storing, retrieving, using, changing and output.

• It documents these activities in data flow diagrams which graphically shows the relation between processes and data, and in data dictionaries.

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• Features of Data Flow strategy:• Data Flow strategy uses both requirement determination and systems design.• It views the activities of a system from the viewpoint of the data: where they originate, how they are used or changed, and where they go, including the stops along the way from their origin to their destination.

• Tools of Data flow strategy:• Data flow strategy shows the use of data in the system pictorially.• It can be difficult to fully understand a business process through a verbal description alone; data flow tools help by illustrating the essential components of a system and their interactions.

• Data flow analysis make use of the following tools:• Data Flow Diagram (DFD)• Data Dictionary (DD)• Data Structure diagram• Structure Chart

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Data Flow Analysis Tools

• Data Flow Diagram (DFD)• A graphical tool to describe and analyse the movement of data through a system – manual or automated – including the processes, stores of data, and delays in the system.

2 types:• Logical DFD

• The transformation of data from input to output, through processes, may be described logically and independentally of the physical components (for eg., computers, file cabinets, disk units, and word processors) associated with the system.

• Physical DFD• They show the actual implementation and the movement of data between people, departments, and workstations.

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Data Flow Analysis Tools

• Data Dictionary• The logical characteristics of current systems data stores, including name, description, aliases, contents, and organization. 

• Identifies processes where the data are used, and where immediate access to information is needed.

• Identifies database requirements during system design.

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Data Flow Analysis Tools

• Data Structure Diagram

• A pictorial description of the relation between entities (people, places, events, and things) in a system and the set of information about the entity.

• Does not deal with physical data storage.

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Data Flow Analysis Tools

• Structure Chart

• A design tool that pictorially shows the relation between processing modules in computer software.

• Describes the hierarchy of component  modules and the data that are transmitted between them.

• Includes analysis of input‐to‐output transformations and analysis of transactions.

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Relation of structured analysis components

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Data Flow Diagram• A DFD lets a system analyst study how existing systems work, locate possibleareas prone to failure, track faulty procedures and reorganise components toachieve better efficiency or effectiveness.

• Components:A data flow diagram graphically represents:• processes ‐ jobs that are done with the data. A process transforms incomingdata flow into outgoing data flow.

• data‐stores ‐ files, databases, archives. They can be manual, digital ortemporary.

• external entities/terminators in a business or other system ‐ other systemsor people beyond the control of the current system. These are the placeswhich provide the organisation with data, or have data sent to them by theorganisation (e.g. customers, partners, government bodies). External entitiesare sources and destinations of the system's inputs and outputs.

• connecting data flows ‐ arrows show how data flows from one place toanother. Flows that cross the system boundary are known as Input OutputDescriptions. Label the arrows with the name of the data that moves throughit.

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Notations for DFDThere are 2 notations available to make DFD:

• The Yourdon and Coad style, • The Gane and Sarson style.• They have slight differences in the way components are shaped and where their numbering goes, for example:

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Gane and Sarson datastore notation

Yourdon and Coad datastore notation

DFD Naming Guidelines

• External Entity  Noun• Data Flow  Names of data• Process  Verb Phrase

• A system name• A subsystem name

• Data Store  Noun

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Context level Diagram

• A data flow diagram (DFD) is a design tool torepresent the flow of data through an informationsystem.

• A "context level" DFD can be used to show theinteraction between a system and outside entities;it can also show the internal data flows within asystem. This version is also called a contextdiagram.

• It often shows the information system as a singlecircular shape with no details of its inner workings:what it shows is its relationships with the externalentities.

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StudentQuiz 

Software System

Submitted Answers

Result/Feedback

Fig 1: Context Diagram (0‐level) for Quiz Software System

• For a diagram to be called a DFD, it needs to showthe inner workings of an information system.

• The different levels of a DFD indicate how detailed itis, e.g. a Level 0 DFD is a broad overview of asystem, showing hardly any detail within thesystem. Level 0 DFD is aka Context Diagram.

• Level 1 DFD:• A level 1 DFD explodes more summarised processes and

shows another level of complexity within them.• The Level 1 DFD shows how the system is divided into sub‐

systems (processes), each of which deals with one or moreof the data flows to or from an external agent.

• It also identifies internal data stores that must be present inorder for the system to do its job, and shows the flow ofdata between the various parts of the system.

• A level 2 or 3 DFD shows even more componentsopened up to show their inner details.

• After context diagram, different levels are termed asDetailed DFD.

• Question: Draw detailed DFD for Quiz softwareSystem from its context diagramBCA205: SA&D 16

Box represents whole system boundary

Context diagram (level 0 DFD)

Level 1 DFD

Level 2 DFD

Fig 2: Relationship between different levels of DFD

Detailed DFD for Quiz Software

17Fig 3: Detailed DFD for Quiz Software System

DFD Conventions/Rules:• Do not allow a single page of a DFD to get too complex ‐ it should have no more than 10 components. If ithas more than this, combine some components into a single self‐contained unit and create a new DFD forthat unit.

• Each component and subcomponent should be numbered. e.g. a top level DFD has components 1 2 3 4 5.The subcomponent DFD of component 3 would have components 3.1, 3.2, 3.3, and 3.4; and thesubcomponent DFD of component 3.2 would have components 3.2.1, 3.2.2, and 3.2.3. This enables adeveloper to plan in a top‐down manner: starting with representing large concepts, and then repeatedlybreaking these objects into their components.

• All processes must have at least one data flow in and one data flow out.

• All processes should modify the incoming data, producing new forms of outgoing data.

• Each data store must be involved with at least one data flow.

• Each external entity must be involved with at least one data flow.

• A data flow must be attached to at least one process.

• Data flows cannot go directly from one external entity to another external entity: such flows need to gothrough at least one process.

• Data flows cannot go directly from an external entity to a data store in the system: such flows need to gothrough at least one process.

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To Do in the class:

• Student Registration System• Context Diagram• Detailed Diagram

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• Student Registration System• Context Diagram

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• Student Registration System• Detailed Diagram

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Assignment:

• Make a Context level diagram for Railway Reservation System.• Also make its detailed DFD diagrams.• Need to email it to notesmicro@gmail.com till 22nd April, 5pm.

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Railway Reservation System

• To Solve • Context Diagram • Detailed Diagram

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Railway Reservation SystemContext Diagram

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PassengerRailway 

Reservation System

Passenger queries/details

Result/Confirmed Ticket/SMS

Railway Reservation SystemDetailed Diagram

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Data Dictionary• A Data Dictionary is a document that describes the basic organization of a database.

• Typically a data dictionary will contain a list of variables in the database as well as the assigned variablenames and a description of each type of variable (e.g. character, numeric, dates).

• The data dictionary should also include the values accepted for each variable, and any helpful commentssuch as important exclusions and skip patterns.

• The data dictionary is used primarily for data analysis.

• Example (Taken from the CDC Manual: Indicators and methods for cross sectional surveys of vitamin andmineral status of populations):

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Variable Variable name Variable type Variable Width Values/notesParticipant ID number ID Numeric 3 001‐900Cluster number CLUSTER Numeric 2 1‐30Age in months AGE Numeric 2.1 6.0‐59.9Date of birth DOB dd/mm/yyyy 1‐31/1‐12/1900‐2011Gender GENDER Numeric 1 1 = male 2 = femaleDate of survey SURVEY dd/mm/yyyy 15/06/2004 – 20/08/2004Hemoglobin HB Numeric 2.1 4.0 – 18.0Iodine IOD Numeric 4.1 0.0 – 1000.0

Assignment:

Make data dictionary for the following systems:1. Student Registration System2. Railway Reservation System

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• Student Registration System

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Variable Variable name Variable type Variable Width Values/notesStudent Roll No. ID Numeric 3 001‐900Salutation SAL Text 2 Mr|MsStudent First Name FNAME Text 10 A‐ZStudent Last Name LNAME Text 10 A‐ZAge AGE Numeric 2.1 6.0‐59.9Date of Birth DOB dd/mm/yyyy 1‐31/1‐12/1900‐1995Gender GENDER Numeric 1 1 = male 2 = femaleCourse Applied For COURSE Text 10 A‐ZSession SESSION Numeric 4 2013‐2014Mobile Phone MOB Numeric 10 9xxxxxxxxx‐9xxxxxxxxxEmail Id EMAIL Alphanumeric 15@5.3.2 notesmicro@gmail.com

• Railway Reservation System

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Variable Variable name Variable type Variable Width Values/notesPNR No. PNR AlphaNumeric XXX‐5 NWR‐12345Train No. ID Numeric 5 00000‐99999Train Name TNAME Alphabets 10 A‐ZTime TIME HHMM 4 0000‐2359Boarding Station BNAME Alphabets 10 A‐ZDestination Station DNAME Alphabets 10 A‐ZCoach Number COACH_NO AlphaNumeric X1 S1‐S6Seat Number SEAT_NO Numeric 2 01‐99Passenger First Name FNAME Text 10 A‐ZPassenger Last Name LNAME Text 10 A‐ZCategory CATEGORY Numeric 1 1 = Adult, 2 = Child, 3 = Senior 

CitizenID Proof Type ID_PROOF Numeric 1 1 = Voter Card, 2 = Ration 

Card, 3 = Driving LicenceDate of Birth DOB dd/mm/yyyy 1‐31/1‐12/1900‐2013Gender GENDER Numeric 1 1 = male 2 = femaleMobile Phone MOB Numeric 10 9xxxxxxxxx‐9xxxxxxxxx

• Convert the following detailed DFD in more apprehend‐able form:

• (Hint: Align all processes together, entities separate and database apart)

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References: 

• Book• Chapter 4: James A Senn ‐ Analysis and Design of Information systems‐McGraw‐Hill International Edition, 1989.

• DFD ‐ Student Registration Form http://viu.eng.rpi.edu/lab/3/s3_2.html• Quiz Software ‐ http://vceit.com/p/dfd.htm• Leveling of DFD: http://www.tutorsglobe.com/homework‐help/software‐engineering/levelling‐of‐dfd‐7766.aspx

• Making DFD online: https://www.draw.io

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