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For Instance, Many Departments And Customers Within A Company Need Access To Various Types Of Data. Each Employee In The Company Will Have A Unique Customised Front-end Application And Varying Levels Of Access To The Database.
Data Is Strictly Arranged In A Row-and-column Format In Databases. The Rows Are Known As Record Or A Triple. One Row Of Data Items May Include Data Items Of Several Data Types. However, The Columns Are Often Referred To As Domain Or Attribute. One Attribute May Include Many Data Items, All Of Which Are Of The Same Data Type.
A Database-management System (Dbms) Is A Group Of Connected Data That May Be Accessed Via A Number Of Programmes. This Is A Database Because It Is A Collection Of Connected Data With An Implicit Meaning. The Database, Which Is The Term Used To Describe The Collection Of Data, Contains Information Pertinent To An Enterprise. A Dbms’s Main Objective Is To Provide A Convenient And Effective Way To Store And Retrieve Database Information. Known Facts That Can Be Noted And That Have Implicit Meaning Are Referred To As Data.
Because It Is Impossible To Maintain The Database Without Some Kind Of Rules And Regulations, The Management System Is Crucial. In Order To Create Relationships Between Two Tables, We Must Choose The Specific Attributes That Should Be Included In Each Table.
We Must Also Decide Which Tables Should Be Handled When A New Record Is Added Or Deleted. In Order To Maintain The Database’s Integrity, These Problems Must Be Overcome By Establishing Some Kind Of Rules That Must Be Followed.
Database Management Systems Are Designed To Handle Large Amounts Of Data. The Definition Of Structures For Information Storage And The Provision Of Mechanisms For Information Manipulation Are Both Components Of Data Management.
Additionally, Notwithstanding System Failures Or Attempts At Unauthorised Access, The Database System Must Guarantee The Security Of The Information Stored. The System Must Guard Against Potential Anomalous Outcomes If Data Are To Be Shared Across Several Users.
Given The Significance Of Information In Most Organisations, Computer Scientists Have Created A Vast Body Of Concepts And Management Techniques. The Emphasis Of This Book Is On These Ideas And Methods. This Chapter Describes The Basic Concepts Of Database Systems.
A Computerised Record-keeping System Is A Database Management System. It Serves As A Collection Point Or Container For Computerised Data Files. Dbms’ Overarching Goal Is To Provide Users The Flexibility To Define, Save, Retrieve, And Update The Database’s Contents As Needed. Anything That Is Important To A Person Or An Organisation Is Considered Information.
As The Need Arises, New Application Programmes Are Added To The System. Consider, For Instance, The Case Where A University Decides To Add A New Major (Say, Computer Science). Consequently, The University Establishes A New Department And Establishes New Permanent Files (Or Adds Information To Already Existing Files) To Store Data On All Of The Department’s Instructors,
Students Who Major In That Major, Course Offerings, Degree Requirements, Etc. To Deal With Rules Particular To The New Major, The University May Need To Write New Application Programmes. To Accommodate New University Rules, It Can Also Be Necessary To Write New Application Programmes. As A Result, The System Accumulates More Files And Application Programmes Over Time.
An Ordinary Operating System Supports This Typical File-processing System. The System Stores Permanent Records In Various Files; To Extract Records From And Add Records To The Appropriate Files, It Requires Different Application Programs. Prior To The Development Of Database Management Systems (Dbmss), Organisations Often Used Such Systems To Store Information. Using A File-processing System To Store Organisational Data Has A Number Of Significant Drawbacks, Including:
Redundant And Inconsistent Data. The Many Files Are Likely To Have Different Structures, And The Programmes May Be Written In Various Programming Languages, Since Different Programmers Have Created The Files And Application Programmes Over A Long Period Of Time. Additionally, The Same Information May Appear Many Times (Files).
The Address And Phone Number Of A Student Who Double Majors In Music And Mathematics, For Instance, May Appear In A File Containing Student Records Of Students In The Music Department As Well As A File Containing Student Records Of Students In The Mathematics Department.
Because Of The Redundancy, Storage And Access Costs Are Higher. Additionally, It Might Result In Data Inconsistency, Which Would Mean That Different Copies Of The Same Data Might No Longer Agree. For Instance, The Records Of The Music Department May Reflect A Changed Student’s Address But Not Elsewhere In The System.
Data Accessing Difficulties. Let’s Say A University Clerk Needs To Know The Names Of All The Students Who Reside In A Certain Postal Code. The Clerk Requests That Such A List Be Created From The Data-processing Department. There Is No Application Programme Available To Meet This Need Since The Original System’s Designers Did Not Anticipate It. However, A Programme May Be Used To Generate A List Of All Students.
The University Clerk Now Has Two Options: Either Get A List Of All Students And Manually Extract The Necessary Information, Or Request That A Programmer Create The Required Application Programme. Both Options Are Obviously Inadequate. Imagine That After Writing Such A Programme, The Same Clerk Has To Trim The List To Only Include Students Who Have Completed At Least 60 Credit Hours.
As Anticipated, There Is No Programme That Can Generate Such A List. The Clerk Has The Same Two Options As Before, None Of Which Is Satisfactory. The Key Takeaway Is That Traditional File-processing Environments Do Not Make It Possible To Get Needed Data Quickly And Conveniently. For General Use, More Responsive Data-retrieval Systems Are Needed.
Data Separation Writing New Application Programs To Retrieve The Appropriate Data Is Difficult Due To Data Being Scattered In Various Files And Files May Be In Different Formats.
Integrity Issues The Database’s Data Values Must Adhere To Certain Consistency Requirements. Consider A Scenario In Which The University Keeps An Account For Each Department And Records The Balance In Each Account. Consider As Well That The University Mandates That A Department’s Account Balance Never Drop Below Zero.
By Including The Necessary Code In The Various Application Programmes, Developers Enforce These Constraints On The System. However, It Is Challenging To Modify The Programmes To Enforce New Constraints. When Constraints Include Several Data Items From Various Files, The Issue Is Exacerbated.
Atomicity Issues A Computer System Might Malfunction Just Like Any Other Device. In Many Applications, It Is Essential That The Data Be Restored To The Consistent State That Was Before The Failure If A Failure Occurs. Consider A Plan To Transfer $500 From Department A’s Account Balance To Department B’s Account Balance.
If A System Failure Occurs While The Programme Is Being Run, It Is Possible That The $500 Was Taken Out Of Department A’s Balance But Not Credited To Department B’s Balance, Leading To An Inconsistent Database State. It Is Obvious That Either Both The Credit And Debit Occur, Or That None Occur, In Order To Maintain Database Consistency.
That Is, The Transfer Of Funds Must Be Atomic—that Is, It Must Occur Completely Or Not At All. In A Traditional File-processing System, It Might Be Challenging To Guarantee Atomicity.
Anomalies In Concurrent-access. Many Systems Allow Several Users To Update The Data Simultaneously For The Sake Of The System’s Overall Performance And Faster Response. In Fact, The Biggest Online Retailers Today May Have Millions Of Shoppers Access Their Data Each Day. Concurrent Updates May Interact In Such A Setting, Which Might Lead To Inconsistent Data. Think About Department A, Which Has A $10,000 Account Balance.
If Two Department Clerks Simultaneously Debit Department A’s Account Balance By, Say, $500 And $100, Respectively, The Outcome Of The Concurrent Executions May Result In An Incorrect (Or Inconsistent) State For The Budget. Consider A Scenario In Which The Programmes Handling Each Withdrawal Read The Old Balance, Divide It By The Amount Being Withdrawn, And Then Write The Result Back.
If The Two Programmes Are Running Simultaneously, They May Both Read The Value $10,000 And Write Back, Respectively, $9500 And $9900. The Account Balance Of Department A May Include $9500 Or $9900 Instead Of The Accurate Value Of $9400 Depending On Who Writes The Value Last. The System Must Continue To Exercise Some Level Of Supervision In Order To Protect Against This Possibility.
However, Providing Supervision Is Challenging Since Data May Be Accessed By Several Diverse Application Programmes That Have Not Yet Been Coordinated.
Another Example Would Be If A Registration Programme Kept Track Of The Number Of Students Enrolled In A Course In Order To Enforce Enrollment Restrictions. When A Student Registers, The Programme Checks The Number Of Courses That Are Currently Registered For, Adds One To The Number If Necessary, And Stores The Number Back In The Database.
Let’s Say That Two Students Register At The Same Time, Bringing The Total To, Say, 39. Even Though Two Students Successfully Registered For The Course And The Count Should Be 41, It Is Possible For The Two Programme Executions To Read The Value 39 And Write Back 40 On The Same Occasion.
This Would Result In An Incorrect Increase Of Just 1. Furthermore, If The Course’s Registration Cap Was 40 Students, Both Of The Students Might Register In The Scenario Above, Violating The Cap.
Issues With Security. The Database System’s Users Shouldn’t All Have Access To The Same Data. For Instance, At A University, The Payroll Staff Only Needs Access To The Database’s Financial Information Section. They Do Not Need Access To Student Records Information. Enforcing Such Security Constraints, However, Is Difficult Because Application Programs Are Added To The File-processing System In An Ad Hoc Manner.
Among Other Things, These Challenges Prompted The Creation Of Database Systems. We’ll See Concepts And Algorithms Used By Database Systems To Address Issues With File-processing Systems In The Sections That Follow.
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