1. 1 An Introduction to Databases Dr Stephen Swift The Intelligent Data Analysis Group Brunel University

2. 2 An 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

3. 3 What is a Database? (1) A Database System is a Computerised Record Keeping SystemA Database System is a Computerised Record Keeping System Rather Like an Electronic Filing CabinetRather Like an Electronic Filing Cabinet The Data can be Added to, Deleted, Modified etc…The Data can be Added to, Deleted, Modified etc… The Data Contained is of the Same TypeThe Data Contained is of the Same Type Would Not Have a Database Containing Patient Records and the Sales Records of a Pet Shop, For ExampleWould Not Have a Database Containing Patient Records and the Sales Records of a Pet Shop, For Example

4. 4 What is a Database? (2) In Large Organisations, a Database System is Usually a Subsystem of a Larger Information SystemIn Large Organisations, a Database System is Usually a Subsystem of a Larger Information System An Information System Supports the Information Handling Requirements of an OrganisationAn Information System Supports the Information Handling Requirements of an Organisation Smaller Organisations Might Just Have a Single DatabaseSmaller Organisations Might Just Have a Single Database A Database Management System (DBMS) is a Software System that Enables Users to Define, Create, Maintain and Control Access to a DatabaseA Database Management System (DBMS) is a Software System that Enables Users to Define, Create, Maintain and Control Access to a Database

5. 5 Why Are Databases Needed? A Huge Amount of Data is Being Collected Every Second of the DayA Huge Amount of Data is Being Collected Every Second of the Day The Data:The Data: –Is Often Complex –Large in Size –Requires Sophisticated Manipulation Databases and DBMS are Essential to Successfully Manage Such DataDatabases and DBMS are Essential to Successfully Manage Such Data

6. 6 An MS Access Database Tables Queries Forms & Reports Forms & Reports Macros & Modules Macros & Modules An MDB File An MDB File

7. 7 Microsoft Access A Stand Alone Database SystemA Stand Alone Database System All Aspects of the Database are Contained in a Single MDB FileAll Aspects of the Database are Contained in a Single MDB File Slow When Handling Huge Volumes of DataSlow When Handling Huge Volumes of Data Can be Used to Create Database ApplicationsCan be Used to Create Database Applications

8. 8 Tables

9. 9 Table Properties (1) Rows (or Records)Rows (or Records) –Shows Occurrences of Patient –Each Row Must be Uniquely Identifiable –The Order of the Rows MUST NOT Be Significant

10. 10 Table Properties (2) Columns (or Fields) –Each Column has a Type, e.g. Number, Text, Boolean, Multimedia, etc… –The Order of the Columns MUST NOT be Significant –Only One Value Should be Associated With Each Column/Row Intersection in the Table

11. 11 Table Properties (3) DomainDomain –A Pool of Possible Values From Which the Actual Values Appearing in the Columns of the Table are Drawn e.g. The Domain of Patient Numbers Includes all of the Possible Patient Numbers, Not Just the Ones Currently in Hospitale.g. The Domain of Patient Numbers Includes all of the Possible Patient Numbers, Not Just the Ones Currently in Hospital –Very Important for Comparing Values from Different Tables

12. 12 The 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 NumberUsually a Number or String, e.g. Patient Number Used to Relate Data Between TablesUsed to Relate Data Between Tables

13. 13 Worked 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” –“Gene ID.xls” –“spellman_yeast_alpha.xls” –“annette2004.ppt”

14. 14 Worked Example (1) We Will:We Will: –Create a Microsoft Access Database –Import Some Data –Make Sure the Fields are the Correct Type –Create Three Tables –Look at the Tables (Datasheet View)

15. 15 Queries (1) A Query Selects or Modifies a Subset of One or More TablesA Query Selects or Modifies a Subset of One or More Tables E.g. All Female Patients Under 18 Years OldE.g. All Female Patients Under 18 Years Old A Query is Often Expressed in a Special Language Called SQLA Query is Often Expressed in a Special Language Called SQL

16. 16 SQL “Structured Query Language”“Structured Query Language” Originally a Proprietary Language from IBMOriginally a Proprietary Language from IBM Now an International Standard High Level Language Supported by Most Database ProductsNow an International Standard High Level Language Supported by Most Database Products Used to Modify Data Within a DatabaseUsed to Modify Data Within a Database

17. 17 Data Manipulation Data is Manipulated by Rows and ColumnsData is Manipulated by Rows and Columns A Subset of Data is Selected and then ModifiedA Subset of Data is Selected and then Modified The Selection is Made by the User, Usually Some Set of RequirementsThe Selection is Made by the User, Usually Some Set of Requirements E.g. Select All Female Patients Under 18 Years Old and Delete All Their RecordsE.g. Select All Female Patients Under 18 Years Old and Delete All Their Records

18. 18 Queries (2) A SELECT Query Selects a Subset of One or More Tables SELECT FROM WHERE ; SELECT Alpha.* FROM Alpha WHERE Alpha.alpha63="NULL";

19. 19 Queries (3) A Make Table Query Creates a Subset of One or More Tables and Puts the Results Into a New Table. The Destination Table is Replaced SELECT INTO FROM WHERE ; SELECT Alpha.* INTO Temp FROM Alpha WHERE Alpha.ORF Like "YP*";

20. 20 Queries (4) An Update Query Changes the Values of One or More Fields in One or More Tables UPDATE SET WHERE ; UPDATE Alpha SET Alpha.alpha63 = "0“ WHERE Alpha.alpha63="NULL";

21. 21 Queries (5) An Append Query Selects a Subset of One Tables and Adds it into Another Table INSERT INTO SELECT FROM WHERE ; INSERT INTO Temp SELECT Alpha.* FROM Alpha WHERE Alpha.alpha63="NULL";

22. 22 Queries (6) A Delete Query Removes a Subset of One or More Tables From the Database DELETE FROM WHERE ; DELETE Alpha.*FROM Alpha WHERE Alpha.alpha63="NULL";

23. 23 Queries (7) A Crosstab Query is Very Complex and Will Therefore Not be Covered!

24. 24 Worked Example (2) We Have Some Import ErrorsWe Have Some Import Errors We Must Locate What Fields are in ErrorWe Must Locate What Fields are in Error We Must Then Use an UPDATE Query to Modify the Erroneous DataWe Must Then Use an UPDATE Query to Modify the Erroneous Data

25. 25 Forms Forms are Used to View/Add/Manipulate Data

26. 26 Data Entry (1) The User Should Only be Able to Enter the Domain of a Field on a FormThe User Should Only be Able to Enter the Domain of a Field on a Form E.g. If There are Only 10 Wards in a Hospital, They Should Only be Able to Enter 1-10 in the Wards FieldE.g. If There are Only 10 Wards in a Hospital, They Should Only be Able to Enter 1-10 in the Wards Field In the Example Above, Allowing Any Number Would Increase the Chance of Data ErrorsIn the Example Above, Allowing Any Number Would Increase the Chance of Data Errors

27. 27 Data Entry (2) Pick Lists and Check Boxes Can Help to Maintain Data IntegrityPick Lists and Check Boxes Can Help to Maintain Data Integrity Validation Rules on Form Fields Can Prevent the User From Entering Invalid DataValidation Rules on Form Fields Can Prevent the User From Entering Invalid Data Minimise Free Text Entry to FieldsMinimise Free Text Entry to Fields The Application Should Help the User in Completing Forms CorrectlyThe Application Should Help the User in Completing Forms Correctly

28. 28 Reports Reports are Used to Display Data

29. 29 Macros and Modules Macros are a User-Defined List of Database Actions to be Carried OutMacros are a User-Defined List of Database Actions to be Carried Out Usually Commonly Performed TasksUsually Commonly Performed Tasks A Module Contains Functions and Subroutines that Carry Out More Complex TasksA Module Contains Functions and Subroutines that Carry Out More Complex Tasks Modules are Constructed Using a Form of Visual BasicModules are Constructed Using a Form of Visual Basic

30. 30 Joins A Join Combines Two Tables into One Virtual TableA Join Combines Two Tables into One Virtual Table Tables are Joined Together Based on a Common Value in a FieldTables are Joined Together Based on a Common Value in a Field The Field That the Two Tables are Joined on Must be the Same TypeThe Field That the Two Tables are Joined on Must be the Same Type

31. 31 Worked Example (3) We Are Going to Join Our Tables TogetherWe Are Going to Join Our Tables Together Using “Tools-Relationships”Using “Tools-Relationships” Add the Three Tables We ImportedAdd the Three Tables We Imported Join “Alpha-ORF” and “Gene ID-ORF”Join “Alpha-ORF” and “Gene ID-ORF” Join “Gene ID-SGD” and “Function- SGD”Join “Gene ID-SGD” and “Function- SGD”

32. 32 Worked Example (4) Now Look at the Effect on:Now Look at the Effect on: –Building a SELECT Query on All of the Tables –The Datasheet View For One of the Tables Without Joins it Would be Very Difficult to Relate and/or Compare Data From Different TablesWithout Joins it Would be Very Difficult to Relate and/or Compare Data From Different Tables –Why is This Important?

33. 33 Normalising a Table Normalisation is: “The Organisation of a System's Attributes into a Set of Compact and Meaningful Tables”

34. 34 Normalising a Table Well Normalised Tables Avoid: –Unnecessary Duplication of Data i.e. No Redundant Datai.e. No Redundant Data –Problems With Modifying, Inserting and Deleting Data N.B. Sometimes Referred to as “Update Anomalies”N.B. Sometimes Referred to as “Update Anomalies”

35. 35 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 Previous StageEach Stage is a Development From the Previous Stage

36. 36 Stages of Normalisation (2) Un-Normalised Form Un-Normalised Form First Normal Form First Normal Form Second Normal Form Second Normal Form Third Normal Form Third Normal Form

37. 37 Un-Normalised Form Column Headings (Field Names) Should be MeaningfulColumn Headings (Field Names) Should be Meaningful Choice of Primary KeyChoice of Primary Key –Must be Unique for the Particular Data Source –May Require Two or More Fields –Use the Smallest Number of Fields Possible –Avoid Textual Keys (Degrades Speed)

38. 38 1 st, 2 nd and 3 rd Normal Form 1st : Separate any Repeating Groups of Fields to Other/New Tables1st : Separate any Repeating Groups of Fields to Other/New Tables 2nd : Separate Fields that Only Depend Upon Part of the Key to Other/New Tables2nd : Separate Fields that Only Depend Upon Part of the Key to Other/New Tables 3rd : Separate any Fields That are Not Directly and Fully Dependent on the Key to Other/New Tables3rd : Separate any Fields That are Not Directly and Fully Dependent on the Key to Other/New Tables

39. 39 Sample Source of Data DRUG CARD Patient No.SurnameForename Ward No.Ward Name Drugs Prescribed DateDrug CodeDrug NameDosage Length of Treatment 923MoneybagsMaurice 10Barnard 20/5/88 CO2355PCortisone 2 pills 3 x day after meals 14 days 20/5/88MO3416TMorphine Injection every 4 hours 5 25/5/88 MO3416TMorphineInjection every 8 hours 3 26/5/88PE8694NPenicillin1 pill 3 x day7 for additional drugs continue on another card

40. 40 After Normalisation SYSTEM:DATE / /AUTHOR Source ID No.:Name of Source: UNF1NF2NF3NF Hospital Drug Card Patient Number Patient Surname Patient Forename Ward Number Ward Name Prescription Date Drug Code Drug Name Dosage Length of Treatment Patient Number Patient Surname Patient Forename Ward Number Ward Name Patient Number Prescription Date Drug Code Drug Name Dosage Length of Treatment Patient Number Patient Surname Patient Forename Ward Number Ward Name Patient Number Prescription Date Drug Code Dosage Length of Treatment Drug Name Drug Code Patient Number Prescription Date Drug Code Dosage Length of Treatment Drug Name Drug Code Patient Surname Patient Forename Ward Number Patient Number Ward Name Ward Number *

41. 41 Tables as a Logical Data Structure Drug Code Dosage Trt Lgth 20/5/88 CO2355P 2 pills 3 x day after meals 14 20/5/88MO3416T Injection every 4 hours 5 25/5/88MO3416T Injection every 8 hours 3 26/5/88PE8694N1 pill 3 x day 7 15/5/88 AS473A 2 pills 3 x day after meals 7 20/5/882 per day 5 Pat No 923 109 VA231M Prescr Date Maurice Ivor Moneybags Foot109 923 Pat No Surname Forename 10 11 Wd No Patient Fleming Barnard 10 11 Wd No Ward Name Ward Prescription Drug Name Cortisone Morphine Penicillin Valium Aspirin Drug Code CO2355P MO3416T PE8694N AS473A VA231M Drug

42. 42 Worked Example (4) Create a SELECT Query that Just Displays the Functional GroupsCreate a SELECT Query that Just Displays the Functional Groups Check that it Contains What We are AfterCheck that it Contains What We are After Change the SELECT Query to a MAKE TABLE QueryChange the SELECT Query to a MAKE TABLE Query

43. 43 References Further Reading and Source for this Presentation:Further Reading and Source for this Presentation: –Database Systems: “A Practical Approach to Design, Implementation and Management”, 3 rd Edition, T. Connolly and C. Begg, Addison Wesley, 2001 –“An Introduction to Database Systems”, 8 th Edition, C. J. Date, Addison Wesley, 2004