An Introduction to Databases

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An Introduction to DatabasesAn Introduction to Databases

Dr Stephen Swift

The Intelligent Data Analysis Group

Brunel University

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An Introduction to DatabasesAn Introduction to Databases

• DatabasesDatabases

• The Parts of a DatabaseThe Parts of a Database

• A Brief Description of SQLA Brief Description of SQL

• Examples Using Microsoft AccessExamples Using Microsoft Access

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What is a Database? (1)What is a Database? (1)

• A Database System is a Computerised Record A Database System is a Computerised Record Keeping SystemKeeping System

• Rather Like an Electronic Filing CabinetRather Like an Electronic Filing Cabinet• The Data can be Added to, Deleted, Modified The Data can be Added to, Deleted, Modified

etc…etc…• The Data Contained is of the Same TypeThe Data Contained is of the Same Type• Would Not Have a Database Containing Would Not Have a Database Containing

Patient Records and the Sales Records of a Patient Records and the Sales Records of a Pet Shop, For ExamplePet Shop, For Example

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What is a Database? (2)What is a Database? (2)

• In Large Organisations, a Database System In Large Organisations, a Database System is Usually a Subsystem of a Larger is Usually a Subsystem of a Larger Information SystemInformation System

• An Information System Supports the An Information System Supports the Information Handling Requirements of an Information Handling Requirements of an OrganisationOrganisation

• Smaller Organisations Might Just Have a Smaller Organisations Might Just Have a Single DatabaseSingle Database

• A Database Management System (DBMS) is A Database Management System (DBMS) is a Software System that Enables Users to a Software System that Enables Users to Define, Create, Maintain and Control Access Define, Create, Maintain and Control Access to a Databaseto a Database

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Why Are Databases Needed?Why Are Databases Needed?

• A Huge Amount of Data is Being A Huge Amount of Data is Being Collected Every Second of the DayCollected Every Second of the Day

• The Data:The Data:– Is Often ComplexIs Often Complex– Large in SizeLarge in Size– Requires Sophisticated ManipulationRequires Sophisticated Manipulation

• Databases and DBMS are Essential to Databases and DBMS are Essential to Successfully Manage Such DataSuccessfully Manage Such Data

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An MS Access DatabaseAn MS Access Database

TablesTables QueriesQueriesForms &ReportsForms &Reports

Macros &Modules

Macros &Modules

An MDBFile

An MDBFile

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Microsoft AccessMicrosoft Access

• A Stand Alone Database SystemA Stand Alone Database System• All Aspects of the Database are All Aspects of the Database are

Contained in a Single MDB FileContained in a Single MDB File• Slow When Handling Huge Volumes of Slow When Handling Huge Volumes of

DataData• Can be Used to Create Database Can be Used to Create Database

ApplicationsApplications

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TablesTables

Patient No.

Patient Surname

Patient Forename Sex Date of

birthWard No.

923 109 854 231 459

Moneybags Foot Hare Knee Legg

Maurice Ivor Susan Boris Brian

Male Male Female Male Male

23/7/53 3/4/41

13/11/61 4/2/31

10/2/70

10 11 10

7 10

Primary key

Foreign key

Column name

Rows

Patient No. Surname Forename Sex Date of birth Ward No.

Male Female 1–12

The Patient table

Ward No.

Ward Name

Type Number of beds

3 11 10

Nightingale Fleming Barnard

Medical Medical Surgical

8 12 21

The Ward table

Domains

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Table Properties (1)Table Properties (1)

• Rows (or Records)Rows (or Records)

– Shows Occurrences of PatientShows Occurrences of Patient

– Each Row Must be Uniquely IdentifiableEach Row Must be Uniquely Identifiable

– The Order of the Rows MUST NOT Be The Order of the Rows MUST NOT Be

SignificantSignificant

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Columns (or Fields)Columns (or Fields)– Each Column has a Type, e.g. Number, Each Column has a Type, e.g. Number,

Text, Boolean, Multimedia, etc…Text, Boolean, Multimedia, etc…– The Order of the Columns MUST NOT be The Order of the Columns MUST NOT be

SignificantSignificant– Only One Value Should be Associated With Only One Value Should be Associated With

Each Column/Row Intersection in the TableEach Column/Row Intersection in the Table

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• DomainDomain– A Pool of Possible Values From Which the A Pool of Possible Values From Which the

Actual Values Appearing in the Columns of Actual Values Appearing in the Columns of the Table are Drawnthe Table are Drawn• e.g. The Domain of Patient Numbers Includes all e.g. The Domain of Patient Numbers Includes all

of the Possible Patient Numbers, Not Just the of the Possible Patient Numbers, Not Just the Ones Currently in HospitalOnes Currently in Hospital

– Very Important for Comparing Values from Very Important for Comparing Values from Different TablesDifferent Tables

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The Primary KeyThe Primary Key

• A Special Type of FieldA Special Type of Field

• Not All Tables Have a Primary KeyNot All Tables Have a Primary Key

• Usually a Number or String, e.g. Patient Usually a Number or String, e.g. Patient

NumberNumber

• Used to Relate Data Between TablesUsed to Relate Data Between Tables

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Worked ExamplesWorked Examples

• Check That Microsoft Access LoadsCheck That Microsoft Access Loads• Check That You Can See Four Files:Check That You Can See Four Files:

– ““Functions.xls”Functions.xls”– ““Gene ID.xls”Gene ID.xls”– ““spellman_yeast_alpha.xls”spellman_yeast_alpha.xls”– ““annette2004.ppt”annette2004.ppt”

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Worked Example (1)Worked Example (1)

• We Will:We Will:– Create a Microsoft Access DatabaseCreate a Microsoft Access Database– Import Some DataImport Some Data– Make Sure the Fields are the Correct TypeMake Sure the Fields are the Correct Type– Create Three TablesCreate Three Tables– Look at the Tables (Datasheet View)Look at the Tables (Datasheet View)

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Queries (1)Queries (1)

• A Query Selects or Modifies a Subset A Query Selects or Modifies a Subset of One or More Tablesof One or More Tables

• E.g. All Female Patients Under 18 E.g. All Female Patients Under 18 Years OldYears Old

• A Query is Often Expressed in a A Query is Often Expressed in a Special Language Called SQLSpecial Language Called SQL

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SQLSQL

• ““SStructured tructured QQuery uery LLanguage”anguage”• Originally a Proprietary Language from Originally a Proprietary Language from

IBMIBM• Now an International Standard High Now an International Standard High

Level Language Supported by Most Level Language Supported by Most Database ProductsDatabase Products

• Used to Modify Data Within a Used to Modify Data Within a DatabaseDatabase

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Data ManipulationData Manipulation

• Data is Manipulated by Rows and Data is Manipulated by Rows and ColumnsColumns

• A Subset of Data is Selected and then A Subset of Data is Selected and then ModifiedModified

• The Selection is Made by the User, The Selection is Made by the User, Usually Some Set of RequirementsUsually Some Set of Requirements

• E.g. Select All Female Patients Under E.g. Select All Female Patients Under 18 Years Old and Delete All Their 18 Years Old and Delete All Their RecordsRecords

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A A SELECTSELECT Query Selects a Subset of One Query Selects a Subset of One

or More Tablesor More Tables

SELECT <Fields> FROM <Table>WHERE <Condition>;

SELECT Alpha.* FROM Alpha

WHERE Alpha.alpha63="NULL";

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A A Make TableMake Table Query Creates a Subset of Query Creates a Subset ofOne or More Tables and Puts the ResultsOne or More Tables and Puts the ResultsInto a New Table. The Destination Table Into a New Table. The Destination Table is Replacedis Replaced

SELECT <Fields> INTO <Destination Table> FROM <Source Table> WHERE <Condition>;

SELECT Alpha.* INTO Temp FROM AlphaWHERE Alpha.ORF Like "YP*";

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An An UpdateUpdate Query Changes the Values of Query Changes the Values ofOne or More Fields in One or More TablesOne or More Fields in One or More Tables

UPDATE <Table> SET <Fields to Values>WHERE <Condition>;

UPDATE Alpha SET Alpha.alpha63 = "0“WHERE Alpha.alpha63="NULL";

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An An AppendAppend Query Selects a Subset of One Query Selects a Subset of OneTables and Adds it into Another Table Tables and Adds it into Another Table

INSERT INTO <Destination Table> SELECT<Fields> FROM <Source Table> WHERE<Condition>;

INSERT INTO Temp SELECT Alpha.* FROM Alpha WHERE Alpha.alpha63="NULL";

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A A DeleteDelete Query Removes a Subset of One or Query Removes a Subset of One or More Tables From the DatabaseMore Tables From the Database

DELETE <Rows> FROM <Table> WHERE<Condition>;

DELETE Alpha.*FROM Alpha WHEREAlpha.alpha63="NULL";

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A A CrosstabCrosstab Query is Very Query is Very

Complex and Will Therefore Complex and Will Therefore

Not be Covered! Not be Covered!

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• We Have Some Import ErrorsWe Have Some Import Errors

• We Must Locate What Fields are in We Must Locate What Fields are in

ErrorError

• We Must Then Use an We Must Then Use an UPDATE UPDATE Query Query

to Modify the Erroneous Datato Modify the Erroneous Data

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FormsForms

Forms are Used to View/Add/Manipulate DataForms are Used to View/Add/Manipulate Data

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Data Entry (1)Data Entry (1)

• The User Should Only be Able to Enter The User Should Only be Able to Enter the Domain of a Field on a Formthe Domain of a Field on a Form

• E.g. If There are Only 10 Wards in a E.g. If There are Only 10 Wards in a Hospital, They Should Only be Able to Hospital, They Should Only be Able to Enter 1-10 in the Wards FieldEnter 1-10 in the Wards Field

• In the Example Above, Allowing Any In the Example Above, Allowing Any Number Would Increase the Chance of Number Would Increase the Chance of Data ErrorsData Errors

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Data Entry (2)Data Entry (2)

• Pick Lists and Check Boxes Can Help Pick Lists and Check Boxes Can Help to Maintain Data Integrityto Maintain Data Integrity

• Validation Rules on Form Fields Can Validation Rules on Form Fields Can Prevent the User From Entering Invalid Prevent the User From Entering Invalid DataData

• Minimise Free Text Entry to FieldsMinimise Free Text Entry to Fields• The Application Should Help the User The Application Should Help the User

in Completing Forms Correctlyin Completing Forms Correctly

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ReportsReports

Reports are Used to Display DataReports are Used to Display Data

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Macros and ModulesMacros and Modules

• Macros are a User-Defined List of Macros are a User-Defined List of Database Actions to be Carried OutDatabase Actions to be Carried Out

• Usually Commonly Performed TasksUsually Commonly Performed Tasks• A Module Contains Functions and A Module Contains Functions and

Subroutines that Carry Out More Subroutines that Carry Out More Complex TasksComplex Tasks

• Modules are Constructed Using a Form Modules are Constructed Using a Form of Visual Basicof Visual Basic

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JoinsJoins

• A Join Combines Two Tables into One A Join Combines Two Tables into One Virtual TableVirtual Table

• Tables are Joined Together Based on a Tables are Joined Together Based on a Common Value in a FieldCommon Value in a Field

• The Field That the Two Tables are The Field That the Two Tables are Joined on Must be the Same TypeJoined on Must be the Same Type

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• We Are Going to Join Our Tables We Are Going to Join Our Tables TogetherTogether

• Using “Using “Tools-RelationshipsTools-Relationships””• Add the Three Tables We ImportedAdd the Three Tables We Imported• Join “Join “Alpha-ORFAlpha-ORF” and “” and “Gene ID-ORFGene ID-ORF””• Join “Join “Gene ID-SGDGene ID-SGD” and “” and “Function-SGDFunction-SGD””

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• Now Look at the Effect on:Now Look at the Effect on:– Building a Building a SELECTSELECT Query on All of the Query on All of the

TablesTables– The Datasheet View For One of the The Datasheet View For One of the

TablesTables

• Without Joins it Would be Very Without Joins it Would be Very Difficult to Relate and/or Compare Difficult to Relate and/or Compare Data From Different TablesData From Different Tables

– Why is This Important?Why is This Important?

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Normalising a Table Normalising a Table

Normalisation is:Normalisation is:

““The Organisation of a System's The Organisation of a System's Attributes into a Set of Compact Attributes into a Set of Compact

and Meaningful Tables”and Meaningful Tables”

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Normalising a Table Normalising a Table

Well Normalised Tables Avoid:Well Normalised Tables Avoid:– Unnecessary Duplication of DataUnnecessary Duplication of Data

• i.e. No Redundant Datai.e. No Redundant Data

– Problems With Modifying, Inserting and Problems With Modifying, Inserting and Deleting Data Deleting Data • N.B. Sometimes Referred to as “Update N.B. Sometimes Referred to as “Update

Anomalies”Anomalies”

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Stages of Normalisation (1)Stages of Normalisation (1)

• Normalisation Takes Place in StagesNormalisation Takes Place in Stages

• Each Stage is Known as a Normal FormEach Stage is Known as a Normal Form

• Each Stage is a Development From the Each Stage is a Development From the

Previous StagePrevious Stage

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Stages of Normalisation (2)Stages of Normalisation (2)

Un-NormalisedForm

Un-NormalisedForm

First NormalForm

First NormalForm

Second NormalForm

Second NormalForm

Third NormalForm

Third NormalForm

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Un-Normalised FormUn-Normalised Form

• Column Headings (Field Names) Should Column Headings (Field Names) Should be Meaningful be Meaningful

• Choice of Primary KeyChoice of Primary Key– Must be Unique for the Particular Data Must be Unique for the Particular Data

SourceSource– May Require Two or More FieldsMay Require Two or More Fields– Use the Smallest Number of Fields PossibleUse the Smallest Number of Fields Possible– Avoid Textual Keys (Degrades Speed)Avoid Textual Keys (Degrades Speed)

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11stst, 2, 2ndnd and 3 and 3rdrd Normal Form Normal Form

• 1st : Separate any Repeating Groups of 1st : Separate any Repeating Groups of Fields to Other/New TablesFields to Other/New Tables

• 2nd : Separate Fields that Only Depend 2nd : Separate Fields that Only Depend Upon Part of the Key to Other/New Upon Part of the Key to Other/New TablesTables

• 3rd : Separate any Fields That are Not 3rd : Separate any Fields That are Not Directly and Fully Dependent on the Directly and Fully Dependent on the Key to Other/New TablesKey to Other/New Tables

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Sample Source of DataSample Source of Data

DRUG CARD

Patient No. Surname Forename

Ward No. Ward Name

Drugs Prescribed

Date Drug Code Drug Name DosageLength of

Treatment

923 Moneybags Maurice

10 Barnard

20/5/88 CO2355P Cortisone2 pills 3 x day

after meals 14 days

20/5/88 MO3416T MorphineInjection every 4 hours 5

25/5/88 MO3416T Morphine Injection

every 8 hours3

26/5/88 PE8694N Penicillin 1 pill 3 x day 7

for additional drugs continue on another card

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After NormalisationAfter Normalisation

SYSTEM: DATE / / AUTHOR

Source ID No.: Name of Source:

UNF 1NF 2NF 3NF

Hospital

Drug Card

Patient NumberPatient Surname Patient Forename Ward Number Ward Name Prescription Date Drug Code Drug Name Dosage Length of Treatment

Patient NumberPatient Surname Patient Forename Ward Number Ward Name

Patient Number Prescription Date Drug CodeDrug Name Dosage Length of Treatment

Patient NumberPatient Surname Patient Forename Ward Number Ward Name

Patient Number Prescription Date Drug CodeDosage Length of Treatment

Drug NameDrug Code

Patient Number Prescription Date Drug CodeDosage Length of Treatment

Drug NameDrug Code

Patient Surname Patient Forename Ward Number

Patient Number

Ward Name

Ward Number

*

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Tables as a Logical Data Tables as a Logical Data StructureStructure

Drug Code Dosage Trt Lgth

20/5/88 CO2355P2 pills 3 x dayafter meals 14

20/5/88 MO3416T Injection every 4 hours 5

25/5/88 MO3416TInjection every 8 hours 3

26/5/88 PE8694N 1 pill 3 x day 7

15/5/88 AS473A 2 pills 3 x day after meals 7

20/5/88 2 per day 5

Pat No

923

923

923

923

109

109 VA231M

Prescr Date

Maurice

Ivor

Moneybags

Foot109

923

Pat No Surname Forename

10

11

Wd No

Patient

Fleming

Barnard10

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Wd No Ward Name

Ward

Prescription

Drug Name

Cortisone

Morphine

Penicillin

Valium

Aspirin

Drug Code

CO2355P

MO3416T

PE8694N

AS473A

VA231M

Drug

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• Create a Create a SELECTSELECT Query that Just Query that Just Displays the Functional GroupsDisplays the Functional Groups

• Check that it Contains What We are Check that it Contains What We are AfterAfter

• Change the Change the SELECTSELECT Query to a Query to a MAKE MAKE TABLETABLE Query Query

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ReferencesReferences

• Further Reading and Source for this Further Reading and Source for this Presentation:Presentation:– Database Systems: “A Practical Approach Database Systems: “A Practical Approach

to Design, Implementation and to Design, Implementation and Management”, 3Management”, 3rdrd Edition, T. Connolly and Edition, T. Connolly and C. Begg, Addison Wesley, 2001 C. Begg, Addison Wesley, 2001

– ““An Introduction to Database Systems”, An Introduction to Database Systems”, 88thth Edition, C. J. Date, Addison Wesley, Edition, C. J. Date, Addison Wesley, 20042004

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An Introduction to Databases