System:A system is  a organized combination of resources workingtogether to convert inputs into useful output. It is derivedfrom a Greek word ‘system’. A system is an organized groupingof interdependent components working together according aplan to fulfill predetermined objectives.

Characteristics of system:         Predetermined Objectives         It can be further subdivided         All components can be interdependent or interrelated

Types of System:        Physical System        Abstract System        Open System        Close System        Deterministic System        Probabilistic System        Introduction System

1.     Physical System :A physical system can be tangible or visible whichcan be touch and also be counted. Physical systemcan be operated statically or dynamically.

2.     Abstract System:It can be conceptual or intangible. For ex:    A model of organization represents theconcept.

3.     Open System:An open system is that interacts freely withoutside environment and also it can be affectedfrom outside environment. When the environment

changes the open system must also change in orderto adopt itself to the environment otherwise itwill be fail.

4.     Deterministic System:Deterministic system operates in a manner that statof the system at a time is already determined andwe can also predict the next state of the systemwithout error.For ex: The output of computer system isdeterministic.

5.     Probabilistic System:The probabilistic system works in a predictablemanner. If we can predict the stat of the systemthen it is probabilistic.For ex: Economic forecasting.

System Analyst:A system analyst is a person responsible for the development of software and hardware solution to the efficient working of the organization. Analystsstudy the environment and problems of an organization to determine whether a new informationmethod can provide solution to the problem.The main job of system analyst is to provide right type of information, in right quantity at the righttime in post effective manner to the management or the end user.

Roles of System Analyst:       Defining IT requirements of organization

       Gathering Data/Facts       Analyzing the problem       Setting priority amongst requirements       Problem solving       Drawing Specification       Designing System       Evaluating System

1.    Defining IT requirements of organization:The most imp and difficult task of an analystis to understand the organization’s requirement’s information. It includes interviewing users finding out what information is they are using in the current system.

2.     Gathering Data/Facts:For gathering data or facts, written documents are important because these documents represent the formal information flow in the system. The analyst studies documents such as input forms, output records, invoices etc to understand how data are passed and used in the present system.

3.    Analyzing the problem:After gathering data or facts the analyst analyses the working of current system and find out to what extent it meet the user’s needs.

4.    Setting priority amongst requirements:In the organization there are many types of users, each user has different types of information needs. It may not e possible to satisfy the requirements of everyone due to limited availability of resources so it is necessary to give priority. The priorities are set on the basis of urgency and importance of user’s need.

5.    Problem solving:The system analyst helps IT users to solve their information problems. In that role he must understand the problem and suggest solutions.

6.    Drawing specification:The analyst obtains the input and output specification for optimal functioning of the system to be developed.

7.    Designing system:Once the specifications are accepted by the management the analyst gets on to the design of the system. The analyst must be aware of the latest design tools for the system designso analyst also knows as architect.

8.    Evaluating system:

An analyst must critically test the performance of the designed system with specifications after it has been in use for areasonable period of time.

SDLC(Software/System Development Life Cycle):It is a well defined process by which a system is planned, developed and implemented. The system development starts with the requirement for improving their business system. There are following activities involves in SDLC :-

       Preliminary Investigation (Problem Identification)

       Feasibility study       System analysis       System designing       Development of software       System testing       Implementation & Evaluation       Maintenance

1.   Preliminary Investigation OR Problem Identification:One of most difficult task of the system analyst is identifying the real problem of the existing system. It defines the user requirements or what the user expects from the new system. This also includes the rough idea of the resource requirements as well as estimated time for completion and number of persons expected to be involve in each phase.

Problem identification helps in :-

                                                                   i.            Defining aproblem

                                                                 ii.            Setting proper system goal

                                                              iii.           

Determining the boundaries of the project by considering the limitations of available resources

2.   Feasibility study:It determine the possibility of either improving the existing system or developing the complete new system. It helps to obtain an overview of the problem and to get rough assessment of whether physical solution exist. The purpose of feasibility study is todetermine whether the requested system successfully realizable.

There are four aspects of feasibility study :-

                                                                                           i.           

Technical feasibility                                                                                         ii.           

Economical feasibility                                                                                      iii.           

Operational feasibility

                                                                                      iv.           

Behavioural feasibility

i.                   Technical feasibility:It involves the required and existing computer system, hardware, software & to whatextent it can support the proposed application. It answers following questions :-

o   Whether the system can be carried out with existing equipments ?

o   Whether the existing software is enough ?o   If a new technology is required how best it can be implemented ?

ii.                Economic feasibility:It involves post benefit analysis to determine the benefit and savings that are expected from new system and compared with costs. It benefits out weight cost then decision is made to design and implement new system.

iii.              Operational feasibility:It concerns with human, organisational and political aspects. It covers technical performance as well as acceptance within the organisation. It determines the general

attitude and job skills of existing personalsand whether any restructuring of jobs will beacceptable to the current user.

iv.              Behavioural feasibility:It includes how strong the reaction of staff will be towards the development of new systemthat involves computer’s use in their daily work. So resistant to change is identified.

          3.   System analysis:It involves detailed understanding of all important facts of the business area under investigation. This require data collection from a verity of sources such as questionnaires, forms, interviews, study of existing documents. It can be involved the direct observation in the organisation and collected documents to understand the whole existing system.

4.   System designing:In this process the primary object is to identify user requirements and to build a system that satisfies these requirements. Design of the system is mainly the logical design that can be sketch on a paper or on a

computer. It includes physical design elements, describes the data to be inputted.

The process involved in manipulation of data & output design represents:-

                                                                   i.            File structure, storage devices etc

                                                                 ii.            Database is also designed in this phase

                                                              iii.            Changes tobe made in the organisational structure of the firm are outlines

                                                              iv.            Input, Output, files, forms and procedures are planned

                                                                 v.            Finally standards for testing, documentation, system control are designed.

5.   Development of software:Development is a phase where detailed design is used to actually construct and build the system. In this phase the system is decided whether to buy commercial software or to develop new customized program with the help of the programmers. The choice depends upon the cost of software and cost of programming.

6.   System testing:

Testing is a process of making sure that the program performs the intended task. Once the system is designed it should be tested for validity. During this phase the system is used experimentally to ensure that software does not fail and it will work according to its specification. It is tested with special test data.

7.   Implementation & Evaluation:This is the final phase of development. It consists of installing hardware, programs, collecting data and organizing people to interact with and run the system. In this phase user actually starts using the system therefore it also involves training of users and provides friendly documentation.Evaluation is the process of verifying the capability of a system after it put into operation to see whether it meets the objective or not. It includes response time, overall reliability and limitations user behaviour.

8.   Maintenance:It is process of incorporating changes in theimplemented existing system.

                                                                   i.           

Enhancement:

Adding new functions or additional capabilityof the system.

                                                                ii.           

Adaptation:Customizing the software to run in a new environment.

                                                              iii.           

Correction:Correcting the bugs in the existing software.

System PlanningData & Fact gathering techniques:The specific methods that an analyst uses forcollecting data about the requirement of a new system are called fact finding techniques.

1.   Interview:In this technique analyst collects information from individuals. It is a formal meeting where the analyst can obtain information about the operation of the present system and requirements of planned system.

Advantages

                                                       i.            It is helpful for gathering information from individuals who do not communicate effectively by writing.

                                                     ii.            It allows discovering areas for unrealistic expectation, misunderstanding to the proposedsystem.

                                                  iii.            Analyst can observe the interviewee’s non verbal communication.

                                                  iv.            This method gives the analyst the opportunity to motivatethe interview to response freely & openly to questions.

Disadvantages                                                       i.            It is very timeconsuming.

                                                     ii.            Success of interview is dependent on system analyst’s human relation skills.

                                                  iii.            Interviewing may be impractical due to location of the interviewees.

Types of interview

                                          i.            Structured Interview:In structured interview interviewer has specific set of questions to ask. All questions prepared in advance and answers arealready available.

                                       ii.            Unstructured Interview:In this method questions and corresponding responses are open ended. This are conducted with a general goal or subject.

          Planning for interview1.    Purpose of interview should be clear. The purpose of          meeting clearly explainedto the all participant so that relevant document can be supplied in advance.

2.    Proper time, duration and place for interview must be selected before so this will allow the participants to scheduled workaccordingly.

2.   Group Communication/Discussion:When information is required from face to face communication but there is not enough time to conduct personal interview, group interviews can be held.

                    Advantages

                                           i.            There are many persons presents so more types of ideas and views can be discussed in short time.

                                         ii.            The comments of one person may prompt other person to contribute facts which they thoughts.

Disadvantages                                           i.            The group may be dominated by a few persons.

                                         ii.            The situation could lead to a verbal fight between the persons and may need moderation.

                                      iii.            Internal politics of an organisation may determine what is said and what is left thus resulting in false picture.

3.   Questionnaires:Questionnaires are special purpose documents that allow the analyst to collect informationand opinions from respondance. This is more structured and formal method of collecting data.

          Advantages

                                           i.            When it is used for group of users, it is relatively cheap.

                                         ii.            A questionnaire can be administered to larger no of individual simultaneously.

                                      iii.            The respondance feelsgreater confidence.

          Disadvantages                                                       i.            All the questions given in questionnaire are usually not answered completely.

                                                     ii.            It is not possible to observe and analyse the respondance body language.

                                                  iii.            Good questionnaires are difficult to prepare.

                                                  iv.            Cost may be high.

Types of questionnaires –                                                                               I.           

Structured – Answer and question are fixed                                                                             II.           

Unstructured – Not fix pattern

4.   On site observation:

It allows the analyst to gain information which cannot be obtained by other fact finding methods. It is also useful when analyst need to actually observe how documents are handled, what processes are carried on etc.          “On site observation provide close view of working of the real system. The analyst can observe people, objects, documents and occurrence of events.”

Advantages                                                       i.            Data collectionby observation highly reliable.

                                                     ii.            It is relatively inexpensive

          Disadvantages                                                       i.            People usually feel uncomfortable when being watched.

                                                     ii.            It is very timeconsuming.

                                                  iii.            Some activitiesmay take place odd time causing a scheduling inconvenience for system analyst.

Elements of system:

A system’s objectives are expressed in terms of output is needs to produce, the inputs arethe data which are processed while the outputi.e. information are the outcome of the process.In addition there are two more components

                             i.            ControlIt makes the system to operate within tolerable performance levels. Control of the system is the decision maker that controls the activities of accepting input, process & producing the output.

                          ii.            FeedbackIt is the information on how well a system isperforming & it is essential for system modifications.System may use feedback for control the information generated by comparing results with acceptable level of performance (standards) and informing the control elements of the difference is termed as feedback.In feedback control the output is fed back toinput. It allows to be majored against some standards and making adjustment in the processing accordingly.

Feasibility Study:Feasibility is a process that identifies , describes and evaluates proposed system and selects the best system for the job. During the study, the problem definition is solved and all aspects of problem to be included in the system are determined. Size of project, cost and benefits are also estimated with greater accuracy. The result of feasibility study is simply a report which is a formal document detailing the nature and scope of the proposed solution.Types-

1.    Technical feasibility2.    Economical feasibility3.    Operational feasibility4.    Behavioral feasibility

1.   Technical feasibility:It determines whether the technology needed for the proposed system is available and how it can be integrated within the organisation.Technical evaluation must also assess whether

the staff have technical expert to understandand use the new technology.

2.   Economical feasibility:The purpose of assessing economical feasibility is to identify the financial benefits and cost associated with the development of the system. Economic feasibility is often known as the cost benefit analysis. To carry out an economical feasibility study it is necessary to estimateactual money value against activities needed for implementing the system.

3.   Operational feasibility:It is concerned with human, organisational and political aspects. It includes two ways–

i.                   Technical performance:It includes issues such as whether the systemcan provide the right information for organisation’s personnel at right time and right place.

ii.                 Acceptance within the organisation:It determines the general attitudes and job skills of existing personnel and whether any changes in job work will be acceptable by thecurrent users.

4.   Behavioral feasibility:It includes how strong the reaction of staff will be towards the development of new systemthat involves computer’s use in their daily work. So resistant to change is identified.

After feasibility study feasibility report is prepared and submitted to the management.

System Design1.  System Model:A logical or mathematical representation of asystem is known as system model.Model can be built for the existing system tobetter understand the proposed system.

2.  Process Modelling:Process modelling is technique which involvesgraphical representation of functions or processes that capture , manipulates, stores or distribute data between a system & its environment or among components within a system. DFD(Data Flow Diagram) is one of the common form of process model.

3.  Logical & Physical design:System design involves two categories-

a.  Logical design:

It is concerned with the specification of major features of the system that would meet the objectives. The delivered product of logical design may be called as a blueprint of a new system.Logical design of a system includes content requirements and some of following components-

                                                                   i.           

Output(Reports & Displays)                                                                 ii.            Input forms

                                                              iii.           

Procedures(Structured of procedures to collect, transforms & output data)

                                                              iv.           

Storage(Requirements for data to be stored inthe database)

                                                                 v.           

Control(Requirements for data integrity, security & procedure for recovery)

b.  Physical design:It requires logical design or blueprint and produces the program specification, physical files or database definitions. It also includes user interface design and selects hardware & software packages.

4.  Input Output Design:

a.  Input Design:Part of the system which deals with the design of the interface through which user communicates with the system and feeds the input data to the system.

b.  Output Design:The part of the system which deals with determining how the output is to be presented, in what format or shape is known as output design of the system. Computer produces displays and print reports that are to be read and used by users therefore the output must be clear and easy to understand.

c.   I/O Forms:It is primary carrier for data or information. They are the user requests for some action. A properly designed form is necessary for efficient functioning of a system. Form is used to –

                                                                   i.            To obtain information efficiently

                                                                 ii.           

Distributes information easily                                                              iii.            Store information effectively and economically            Types of Forms:

1.  Action Form:This type of form requests the user to perform certain actions and they are generally moves from one person to organisation or another person.

2.  Memory Form:It record historical data such as stock ledger, purchase record, bond form.

3.  Report Form:It provides summarised information. These aregenerally used by managers and such people who are required to make decision making. They guide supervisors and administrators fordecision making.

Form designing:Steps for form designing-

                                                                               i.           

Define the purpose of form                                                                             ii.           

Specify its data contents                                                                          iii.            Usinga guide sheet enter title, form number and indicates position of any specially located material

                                                                          iv.            Reviewwith the user & revised if necessary

                                                                             v.           

Create few test forms.

Output Design1. Designing layout:The arrangement of information on a monitor screen or printed on a paper is termed as layout. The output design is specified on layout forms, sheets that describe the location such as length andtype of text, format of column headings,pagination, etc.

2. Category of output:                                          i.            External                                       ii.            Internal

3. Report generation:Printed reports are formal documents that provide users with the information so that users can perform their jobs effectively. It must be clear and easy to understand. We have to consider some features while designing a report such as : titles, subtitles, date, page no and summary.

4. Design of screens:The reports which are to be shown on a computer screen must be given a clear instruction how a user proceed to retrieve the information. It also include some facility such as user friendly message or pop ups for helping the users.

5. User interface design:A User Interface is a combination of menus, screen design, keyboard commands and language which together create the way a user interacts with the system. Itdetermines how user interacts with system. The hardware part of user interface consists of monitor, keyboard and mouse. The software part of interface determines what things look like on the screen and how user gives commands to get work done.

Features of good user interface:

                                                                  i.            Know the prospective users of the system and their requirements.

                                                               ii.            The interface should be robust i.e. the interface should not be fail because of some erroneous actions taken by the user. It requires sufficient checks to prevent the users from taking some falseactions.

                                                            iii.            If feasible, graphical icons must be used so that key-strokes can be minimised.

                                                             iv.            Test the user interface on actual users.

                                                                v.            Practice iterative (repeated) design.

E-R ModelE-R Model:ER model is a detailed logical representationof entities, association and data elements for an organisation. This technique is used in database design that helps to describe howentities in an organisation are related to another.It includes three features for describing data-

(1)           Entity:It can be person, place, events to the organisation & about which data are captured,stored or processed.

(2)           Attribute:Various types of data elements that describe an entity are known as attributes.For Ex:An entity employee can have attributes such as name, date of birth, address etc.

(3)           Relationship:An association of several entities in an ER model is called relationship.

Different symbols used in ER model:

Decision Tree:Decision tree is a graphical representation that presents conditions and actions sequentially. It is a method of showing the relationship of each condition & its permissible actions. The route of the tree isstarting point and it proceeds towards the various possible nodes.          The size of the tree will depend upon the number of conditions & actions. Eachcondition is expressed in two ways True/Falseor Yes/No.

Advantages of Decision tree 1.    It expresses the logic of if then else in pictorial form.

2.    It is useful to express the logic when a value is variable or an action is dependent on nested decision i.e. the outcome of another decision.

3.    It helps the analyst to identify the actualdecision to be made.

4.    It is used to verify logic and problems that involve a few complex decision and limited number of actions.

Disadvantages of Decision tree 1.    The lack of decision tree is that there is absence of information in its format to take what other combinations of conditions to test.

2.    A large number of branches with many paths will confuse rather than help in analysis.

 Ex:Draw a decision tree for policy followed by acompany in giving discount to its customers as follows.

1.    If transaction is on credit and customer’s record is good the order will be accepted butdo not give any discount.If customer’s record is not good do not accept any order.

2.    If transaction is on cash and sells amount is more than 100 rupees discount will be given 20%.

3.    If transaction is on cash and sells amount is between 50 & 100 rupees than discount willbe given 10%.

4.    If transaction is on cash and sells amount is less than 50 rupees, order is accepted butno discount will be made.

Decision TableA decision table is a graphical method for explaining the logic of making decision in tabular format. It is a set of conditions + set of actions and different combinations of decisions.“It is a matrix representation of logic of decisions which specify the possible conditions for decision and resulting actions.”

The decision table is divided into two parts:1.    Condition2.    Action

1.    Condition:The condition part specifies all conditions that are applied to the inputted data. It is also divided into two parts à

                                                       i.            Condition Stub:-It describes the conditions that exist in theprogram logic.

                                                     ii.            Condition Entry:-It provides answers to questions asked in thecondition asked in the condition term.

2.    Action:

The action part is subdivided into two parts à

                                                       i.            Action Stub:-It describes the action to be taken to meet each condition.

                                                     ii.            Action Entry:-It describes the appropriate action resultingfrom the answer to the condition in conditionentry.

Format:Table Heading Decision

RuleCondition Stub Condition

EntryAction Stub Action

Entry

Advantages of Decision Table1.    It provides compact representation of decision making process.

2.    It is easier to understand particular path.3.    It can be changed according to situation.4.    These are best suited for calculating discounts, commissions or inventory control procedures.

5.    The structure of decision table promotes a logically complete and consistent problem definition.

Disadvantages of Decision Table 1.    It cannot express the complete sequence of operations to solve a problem therefore it may be difficult for the programmer to translate decision table into program.

2.    If there are too many alternatives, it is difficult to list in decision table.

3.    It does not show the flow of logic for the solution to a given problem.

Q:  An insurance company uses the following rule to determine the eligibility of a driverfor insurance.          The driver will be insured if:-

1.    The driver lives in the city with population less than 5000 and he is married man.

2.    The driver lives in the city with population less than 5000 and he is married and age is over 30 years old.

3.    The driver lives in the city with population is 5000 or more and it is married female.

4.    The driver is male over 30.5.    The driver is married and under 30.

Q:Study

following conditions and draw a decision table:-

1.    If product code=AAnd customer type=1And the order amount<=700Then 5% discount allowed

2.    If product code=AAnd customer type=2And the order amount<=700Then 7.5% discount allowed

3.    If product code=AAnd customer type=1And the order amount>=700Then 7.5% discount allowed

4.    If product code=AAnd customer type=2And the order amount>700Then 10% discount allowed

Condition

Rule1 Rule2 Rule3 Rule4 Rule5 Else

Lives incity population<5000

Y Y N - - -

Male Y - N Y - -Married Y Y Y - Y -Age>30 - Y - Y N -Action Rule1 Rule2 Rule3 Rule4 Rule5 Els

eInsured Y Y Y Y YUninsured

Y

5.    A flat discount of 5% on product code=B regardless of customer type and the order amount

Q: Drawadecisiontablefor acompanywiththreeperson A,B,C whose share in the company are 50%,20%,30% sequentially. Any low arises in the company will be passed if it is supportedby share holders and whose share holding exceed 2/3 of the total shares.

Condition Rule1

Rule2

Else

A 50% Y Y -B 20% N Y -

Condition Rule1

Rule2

Rule3

Rule4

Rule5

Else

Product code=A

Y Y Y Y N -

Customer type=1

Y N Y N - -

Order amount<=700

Y Y N N - -

Action Rule1

Rule2

Rule3

Rule4

Rule5

Else

Discount 5%

Y Y

Discount 7.5%

Y Y

Discount 10%

Y

No Discount

Y

C 30% Y N -Action Rule

1Rule2

Else

Low Passed Y YLow Rejected

N

Q: A Co-operating bank xyz granted loan underfollowing conditions draw decision table and tree-

1.    If a customer has a account with the bank and has no loan outstanding (no dues), loan will be granted.

2.    If a customer has an account is outstandingfrom previous loan, loan will be granted if special management approval is obtained.

3.    Reject loan application in all other cases.Condition Rule

1Rule2

Else

Customer has Account

Y Y -

No Out-standingloan  amount

Y N -

Special Management Approval

- Y -

Action Rule1

Rule2

Else

Loan Application Accept

Y Y

Loan Application Reject

Data Flow Diagram (DFD):It is a logical model that describes what take place in an existing system, or proposed system; it does not specify howthe activities are accomplished.            It shows the flow of data and the flow of logic involved.

Characteristics of DFD:                                i.            It focuses on the process that

transforms incoming data flows (Input) into outgoing data flows (Output).

                              ii.            It shows the passage of data through the system.

                            iii.            This diagram also known as bubble chart.

                             iv.            DFD supports a top down approach for analysis that is an analyst begins with general understanding of system then draws each component’s details.

Symbols used in DFD:1.      External Entity:

It is a source or destination of data; it may be person, organisation or other entity that interact with the system.For ex: Customer, supplier;

            The entity supplying data is known as source & those that consume data or give output are called sinks.

2.      Data Flow/Flow line:

It shows how data travels from one point to another point indiagram.

3.      Process: 

It shows the transformation of input data flows to output data flows.            All processes are numbered in DFD for easy identification. Numbering follows a left to right convention. Name of the process describes what happened to the data as it flows through the process.

4.      Data store:

It is warehouse for data

Module SpecificationModule is the way to improve the structure design by break down the problem for solving it into independent task.

Advantages of Module –                               I.            It breakdown the problem into

independent modules so the complexity of the problem can be minimized.

                             II.            Each independent module can beeasily assigned to the various members of the development team.

                          III.            Module can be easily run and tested independently from another.

Top-Down design approach:-It is a technique of breakdown a problem into majortasks to be performed. Each task is then further broken down into separate sub task and so on until each sub task is sufficiently simple to be written as a self contained module.            In Top-Down design we initially describes the problem at the highest level that descript what must be done and It does not show howit must be done. Top-Down methods are used throughout the system analysis and design process. The value of using top-down approach, starting at general level and to understand and gain the systemand moving down to the levels of greater details.

Advantages of Top-Down Approach –

                               I.            By dividing of the problem into number of sub problems we have made it easier to share problem development.

                             II.            It is easy to debug a large program as a number of smaller units rather than one big problem.

                          III.            It is good way to delay decision on problems whose solution is not readily prepared.

                          IV.            It allows a programmer to remain on top of a problem and view the developing solutions. The solution always proceeds from the highest level to the lowest level.

                            V.            It becomes an ideal structure for managing the implementation of a computer program using team of programmers.

Bottom-Up design approach:-When we face a large and complex problem , it is difficult to see how the whole thing can be done soit may easier to solve the part of the problem individual, taking the common and easy aspects first and then more difficult task and finally gather them all together to form complete solution,this is called bottom-up approach.            The bottom-up approach suffers from disadvantage that the part of the program may not fit together very easily and there may be a lack ofconsistency between modules and reprogramming have to be done.

Module Cohesion & Coupling:-                           i.)            Modules:

Module is represented by a rectangle box with module name. After defining general purpose of eachprogram it is divided into modules. Each of which performs a single function.For Ex:-            An accounting system consists of many separate modules that are invoked one at a time as user wish to perform particular function. Each upper level module leads to using one or more lowerlevel modules until the desired function is performed.

                         ii.)            Connectors:Connections between modules are represented using links, modules. It is drown by on arrow line in downward direction.

                      iii.)            Coupling:It refers to the strength of relationship between modules in the system. Coupling measures the degreeto which two distinct modules are bound together.It can be of two types –

a)     Data Coupling:It carries data between two modules and it can have upward or downward direction. Data flows are shown using named arrow with a small circle at one end. It is shown by an arrow with blank circle at the tail.

b)    Control Coupling:It carries info about data couple and does not carry any data. It is shown by an arrow with filled circle at the tail.

                      iv.)            Cohesion:It is used to denote the intra module strength. It is a relationship among elements within a module. Asystem designer should aim at minimizing coupling and maximizing cohesion to get modular design. Designer insures that each module performs a specific function and can be developed independently. A good design has low coupling i.e. low interdependence between modules and high cohesion i.e. high interrelationship within the elements of a single module.            Using Top-Down approach to plan the software for a system is no guarantee that errors will be avoided totally so properly modularized, cohesive system, the contents of the module are designed such that they perform a specific functionand easily understood by people.

Data DictionaryIt is store house of data, giving information aboutdata. During system implementation it serves as common base for programmers who are working on the system, It compares their data description. It is also an important step in building database.            “Data dictionary contains description &definition consulting the data structure, data elements, their interrelationship & other characteristics of a system.”Objectives of Data Dictionary

                                i.            A standard definition of all terms in a system i.e. each data item is uniquely identified and defined.

                              ii.            Easy cross referencing between subsystem’s program and modules.

                            iii.            Simple program maintenance.                           iv.            It contains information about

the data of the system and there is an entry in thedata dictionary for every element of DFD. Thus DFD and Data Dictionary are compliment of each other.

Data Items:There are three classes of data items –

a.     Data Element –                                    It is the smallest unit of data which cannot be meaningfully decomposed further.For Ex:            Employee code, unit of measurement

b.     Data Structure –                                    A group of dataelements forms a data structure.

For Ex:            Data Structure of employee consist of agroup of data elements such employee code, name, age, experience, phone no., address etc.

c.      Data Flow & Data stores –                                    Data flows are data structures in motion whereas Data stores are data structure at rest. Data stores may be files, database etc.

Format of Data Dictionary:A data dictionary is organised into five sections –

                                                        i.            Data Elements                                                      ii.            Data Flows                                                    iii.            Data Store                                                   iv.            Process                                                     v.            External Entities

Data Dictionary lists all data elements, flows, stores, process of the system and it gives the detail about each item in following format –Data types, data name, data description, data characteristics, data control information, composition, physical location of data, etc.

Data dictionary for data element Employee code in dictionary –

Data Element  -           Employee codeDescription      -           Unique code assigned for each employeeType                -           charLength             -           4Range              -           0-9999Data Stores     -           Employee table, Payroll table

Structured English:It is used to provide step by step specification for any algorithm. It can be used at any desirable level of description & procedures. It is modified form of English that is used to specify the contents of the process box in data flow diagram (DFD). It uses English language instead programminglanguage.            It uses there basic types of statementsto describe a process –

                                i.            Sequence structure –                                                It is a single step or action included in a process. It does not depend on the existence of any condition.For Ex:To buy a computer science book we follow the steps –

a.     Pick out a desirable book.b.     Take it to the sells counter.c.      Pay cash for the book.d.     Collect cash receipt.e.     Collect the book and leave the store.

It is used when two or more actions can be taken depending on the value of a specific condition. We can describe it by using following example –If             Book found on the storeThen             Take the book to sales counter            Pay cash            Take receipt & book            Leave store

Else            Do not take book            Leave store.

                              ii.            Iterative structure –                                                In various operating condition it is common to find that certain activities are repeatedly executes while certain conditions exist. It permits analyststo describe these conditions.Until the category of student is SC            Do give the discount to students on fee50%            Take next studentEnd Until

Testing:It is a process to check the software or system whether it gives the required output or not, on given set of data.It other terms we can say it is a process to fail particular system because in testing we prepare all possible set of data and apply tothe system to check it gives expected output so system must give expected output or must be properly shutdown in abnormal cases.

Testing can be categorised into –1)    Black Box Testing2)    White Box Testing

1)   Black Box Testing It emphasizes on input data and expected output of the system. It does not includes the process from which the inputted data converts into required output such as internal control conditions, loop statements etc.

2)   White Box Testing In white box testing we emphasizes on each & every step from which data moves and convertsinto required output such as control statement, repetitions, constraints, comparisons etc.

System quality control & assurance:When a system is designed, it must fulfil the goal of the organization so some control must be developed to ensure a quality system.

            Quality assurance defines the objectives of the system that is what is expected from the system. Quality assurance activity in the system development involves four types of sub activities –

                               I.            Verification-It is a process of confirmation as what is suppliedas per system specification to the system. Verification controls are carried out under given environment and test results are obtained for acceptance of the new system.

                             II.            Validation-Validation is a process of using system in actual environment in order to find errors and checks whether the validations applied to the system are working properly or not. If the results obtained from the system are proper, the system is valid otherwise it is not valid.

                          III.            System testing-It is a review of specification, design and coding.It may be based on feedback obtained from the users.

                          IV.            Certification-

It is a confirmation of the correctness of the program. It provides authenticity of the system design that whether the system is according to its predefined standards and objectives or not.

File structure–A file is a collection of records which are relatedto each other. The size of file is limited by the size of memory and storage medium.Two characteristics determine how the file is organised:

                                                        I.            File Activity:It specifies that percent of actual records proceeds in single run. If a small percent of record is accessed at any given time, the file should be organized on disk for the direct access in contrast.If a fare percentage of records affected regularly than storing the file on tape would be more efficient & less costly.

                                                      II.            File Volatility:It addresses the properties of record changes. File records with many changes are highly volatile means the disk design will be more efficient than tape.

File organisation –A file is organised to ensure that records are available forprocessing. It should be designed with the activity and volatility information and the nature of storage media, Other consideration are cost of file media, enquiry, requirements of users and file’s privacy, integrity, security and confidentiality.There are four methods for organising files-

1.      Sequential organisation2.      Indexed Sequential organisation

3.      Inverted list organisation4.      Direct access organisation5.      Chaining

1.       Sequential organization:Sequential organization means storing and sorting in physical, contiguous blocks within files on tape or disk. Records are also in sequence within each block. To access a record previous records within the block are scanned. In a sequential organization, records can be added only at the end of the file. It is not possible to insert a record in the middle of the file without rewriting the file.In a sequential file update, transaction records are in the same sequence as in the master file. Records from both the files are matched, one record at a time, resulting in an updated master file. In a personal computer with two disk drives, the master file is loaded on a diskette into drive A, while the transaction file is loaded on another diskette into drive B.  Updating the master file transfers data from drive B to A controlled by the software in memory.Advantages:

i.                     Simple to designii.                   Easy to programiii.                  Variable length and blocked records availableiv.                 Best use of storage space

Disadvantagesi.                     Records cannot be added at the middle of the file.

2.       Indexed sequential organization:

Like sequential organization, keyed sequential organization stores data in physicallycontiguous  blocks. The difference is

in the use of indexes to locate records. There are  three areas in disk storage: prime area, overflow area and index area.

The prime area  contains file records stored by key or id numbers. All records are initially stored in the

prime area.

The overflow area  contains records added to the file that cannot be placed in logical sequence in the  prime

area.

The index area  is more like a data dictionary. It contains keys of records and their locations on the

disk. A pointer associated with each key is  anaddress  that tells the system where to find a record.

Advantages:i.                     Indexed sequential organization reduces the magnitude of

the sequential search and provides quick access for sequential and direct processing.

ii.                   Records can be inserted in the middle of the file.

Disadvantages:i.                     It takes longer to search the index for data access or

retrieval.ii.                   Unique keys are required.iii.                  Periodic reorganization is required.

3.       Inverted list organization:Like the indexed- sequential storage method the inverted list organization maintains an index. The two methods differ, however, inthe index level and record storage. The indexed sequential method has a multiple index for a given key, where as the inverted list method has a single index for each key type. In an inverted list, records are not necessarily stored in a particular sequence. They are placed in the data storage area, but indexes are updated for therecord key and location. The inverted keys are best for applicationsthat request specific data on multiple keys. They are ideal for static files because additions and deletions cause expensive pointerupdating.

Advantagesi.                     Used in applications requesting specific data on

multiple keys.

Example:Data for the flight reservation system. 

The flight number, description and the departure time are as given as keys. In the data location area, no particular sequence is followed. If a passenger needs information about the Houston flight, the agent requests the record with Houston flight. The DBMS carries a sequential search to find the required record. The output will then be That the flight number is 170 departing at 10.10 A.M and flight number 169 departing at 8.15 A.M.

if the passenger searches for information about a Houston flight that departs at 8.15,then the DBMS searches the table and retrievesR3 and R6. Then it checks the flight departure time and retrieves R6 standing for flight number 169.

4.       Direct access organization:In direct access file organization, records are placed randomly throughout the file. Records need not be in sequence because they are updated directly and rewritten back in the same location. New records are added at the end of the file or inserted in specific locations based on software commands.Records are accessed by addresses that specify their disk locations. An address is required for locating a record, forlinking records, or for establishing relationships. Addresses are of two types:

i.         Absoluteii.       Relative.

A absolute address represents the physical location of the record. It is usually stated in the format of sector/track/record number. One problem with absolute address is that they become invalid when the file that contains the records is relocated on the disk.A relative address gives a record location relative to the beginning of the file. There must be fixed length records

for reference. Another way of locating a record is by the number of bytes it is from the beginning of the file. When the file is moved, pointers need not be updated because the relative location remains the same.Advantages:

i.                     Records can be inserted or updated in the middle of the file.

ii.                   Better control over record allocation.

Disadvantages:i.              Calculating address required for processing.ii.             Impossible to process variable length records.

5.       Chaining:File organization requires that relationships be established among data items. It must show how characters form fields, fields form files and files relate to each other. Establishing relationship is done through chaining. It uses pointers

Example: The file below contains auto parts that are an indexed sequential file sequenced by part no. A record can be retrieved by part no. To retrieve the next record, the whole file has to be searched. This can be avoided by the use of pointers.

System Security:System security is a process to protect the system from damage, error and unauthorized access. The level of protection depends upon the sensitivity of data, the reliability of the user and the complexity of the system. A well designed system includes control procedures to provide physical protection, maintenance, data integrity and restrict system access.The system security includes for related issues –

                               I.            System integrity:It refers to proper functioning of hardware and programs, safety against external threatssuch as eavesdropping.The data integrity makes sure that data do not differ from its original form and have not been accidently or intentionally disclosed, altered or destroyed.

                             II.            System security:It refers to the protection of data from loss, disclosure, modification and destruction.

                          III.            Privacy:It defines the rights of the user or organisation to determine what information, we want to show or accept from other and how

organisation can be protected against unfair or excessive dissemination of information.

                         IV.            Confidentiality:It is a special status given to the sensitiveinformation in the database for privacy.

Threats to the system security:a.     Errors and omissionsb.    Firec.     Natural  disasterd.    External attacke.     Disgruntled and dishonest employees.

Maintenance:Once a system has been installed and fully operational then the task of system maintenance begins. The maintenance programming term involves keeping the software operational that is undertaking preventive measures to keep computer program running, monitoring the systems operations,fixing problems if any and modifying programs in response to user requirements.

Types of maintenance:                               I.            Corrective                             II.            Adaptive                          III.            Perfective

                               I.            Corrective maintenance:It is performed to correct any errors in newly implemented system.The errors that can occur in the system –

                                                     i.)            Logical error (Program logic error)

                                                   ii.)            System error (hardware problem like disk crash, memory overflow etc.)

                                                 iii.)            Operational error-It occurs due to inappropriate computer schedules. Ex:

        Improper backup of computer files.        Failure to change printer ribbon.                                                iv.)            User error - It

occurs due to deficiency of user training.

The maintenance programmers repair such errors by redesigning the modules in the implemented softwaresystem.

                             II.            Adaptive maintenance:It performs to cope up with the changing environment of the market and organisation. It is performed with a view to keeping the software up todate. This is because, as internal and external business condition changes the data processing requirement also changes. It begins with a request for service from users. Then the request is approved by committee. Then maintenance programmer start work for new requirements.

                          III.            Perfective maintenance:It is performed to further improve the efficiency of working system. Modifying data structure, bakingrecords, eliminating temporary work files etc are some methods of improving overall system performance.Some ways to improve efficiency are –

                                                     i.)            Improving loops and calls to external procedures.

                                                   ii.)            Improving the evolution of algebraic expressions.

                                                 iii.)            Modifying expensive parts of the system.