Mr C Johnston ICT Teacher www.computechedu.co.uk G057 - Lecture 02 Introduction To Database System Concepts Mr C Johnston ICT Teacher www.computechedu.co.uk

Session Objectives Learn about database terminology. To learn the basic relational database components and concepts To become familiar with the relational tables components and characteristics To learn how keys are used in the relational database environment To examine basic entity relationships To draw basic entity relationships

Databases and DBMS A database is a collection of data Databases need to be managed by computer software known as a Database Management System (DBMS) The DBMS is responsible for allowing you to CRUD (Create Read Update Delete) the data Microsoft Access is an example of a DBMS - not a database.

A Logical View Of Data An entity is a person, place, event, or thing for which we intend to collect data Within a university entities could be – A Student, Faculty Member, Course or module An airline may have these entities – A Passenger, Pilot, Aircraft, Route or Supplier Each entity has a number of characteristics which are known as attributes A Student could have – A Student ID, Name, DOB, Home Address, An Aircraft could have – An Aircraft ID Number, hours flown, last maintenance date, Notice that entities are singular as they represent ONE item of data

A Logical View Of Data Entities normally have a number of instances or occurrences which makes sense as lots of students make up a school, This is know as an entity set. The STUDENT entity set contains all the student entities The FACULTY entity set contains all the faculty entities The AIRCRAFT entity set contains all the aircraft entities An entity set is known when we design databases as a table.

Summary of A Relational Table

Database Keys Each entity needs a primary key, This is an attribute which can be used as a unique identifier for a single entity occurrence, studentID could be a primary key for a STUDENT entity Entities can also have secondary keys, A secondary key is used to make an index of attributes which are commonly searched or sorted on, studentName could be a secondary key for the STUDENT set of entities keys also help define relationships between entities, When a relationship is formed between entities the primary key of one will appear as a foreign key in another to create a link.

Database Keys Example relationship using a primary key and a foreign key

Entity Relationships A relationship is a link or association between entities. Normally one dentist has many patients There are three types of relationships: One – to – One A car has one engine size One – to – Many A landlord has many houses Many – to – Many A chocolate bas has many ingredients BUT An ingredient can be used in many different chocolate bars Due to database rules however we only use One – to – many when designing databases. One – to – One relationships are pointless and attributes get collapsed into one entity, Many – to – Many relationships cant exist as the data cant be linked properly and makes no sense which instance relates to which

Entity Relationships Diagrams This is a way of showing relationships between entities, Entity names are always written in capitals and appear in rectangles, Lines join entities together and have: Symbol to show the degree of the relationship, A description to show the name of the relationship,

Entity Relationships Diagrams EMPLOYEE COMPANY CAR drives WARD PATIENT holds ALBUM SINGERS features

Many – To – Many Resolve Many - to – Many relationships are not allowed so we have to resolve them some how. To do this we introduce an additional entity between them Thus creating 2 one - to – many relationships.

Exercises Make a brief description (1/2 page) about the role of the DBMS Write down 3 examples along with a description of uses a company could have for a database Draw an entity relationship diagram to show the relationship between Product and Component House and Street Pet Owner and Pet Draw an entity relationship diagram providing a many – to – many resolve to show the relationship between Customer and Video in a rental shop Student and Course in a school Patients and Medicine in a hospital