Relational Databases

Lecture 1 - Introduction to the module & databases Emma-Jane Phillips Pandon 122 Relational Databases

Relational Databases • Welcome to the module • How the module is organized and assessed • What YOU need to do to pass this module • Database fundamentals • Summary

The module is taught with 1hr Lecture and 1 hr seminars • You must make notes in lecture (in addition to the printed booklet) • There are NO handouts other than the printed booklet • You are expected to do additional reading between lectures and it is assumed that you will have done this • You MAY record the lectures provided you ASK, you may NOT video the classes and you do not have permission to distribute the recordings. • Seminars must be attended, if you miss the seminar you WILL fall behind, most tutors will NOT see you outside of a seminar. • If you do not understand ASK! • This module is assessed by Exam and In-class tests (milestones) • There is an exam in week 8 (reading week) worth 50% • Milestones are worth 12½ % each and are in week 13 of semester 1, and weeks 3, 8 and 13 of semester 2 • If you miss any of these assessment you WILL RECIVE A MARK OF 0.

The new regulation means that students MUST ATTEMPT ALL ASSESSMENT on their module. They cannot pass the module if they do not attempt all parts of it. This means even if they have 80% overall, if they have missed one part worth 5% of the module, they will not be able to pass the module. This will come into effect for all assessments this academic year 2009-2010. New Assessment regulation

Relational Databases and SQL • So, some questions to start with… • What is a database • What is a relational database? • What are the components of a • relational database? • What is SQL?

What is a database? • “a collection of data that is permanently stored on a computer” • A database must be able to: • Hold different types of data in a collection • Record the relationships between the different items in the collection • Have a capacity for range of sizes (e.g., small, medium, large) • We need to be able to: • Insert new data, delete obsolete data & amend existing data in the collection • Retrieve data in the collection in a variety of ways • Manage the collection so that the data can be permanently stored and protected from corruption or loss

What data can we hold? • A data collection (database) should be able to hold a range of data types • Images • Audio files • Text • Numerical • Date • Video • Maps • Etc. The quick brown fox jumped over the lazy fox 26th August 1972

There needs to be a special piece of software to manage the database if the benefits are to be obtained • VERY complex to write so don’t want to have to write our own programs to do this • Therefore, buy a suitable database management system (DBMS) • Change the database (DB) contents to keep them up to date • Find and retrieve data from the DB • Protect data for accidents and intruders • Store in an effective way on the computer Database Management Systems (DBMS) The DBMS is covered in later sessions

In reality databases hold only certain types of data in a true relational database form, we are looking at RDB in this course and although we need to be aware to the theoretical possibilities we are mainly focusing on the real world situation. • A relation is just a logical structure that contains related data (hence the term relation) it is commonly referred to as table but the correct term is relation (books will use either term) • A relation/table may hold the name, address, date of birth, enrolment number of a student. All the data in one collection or row would relate to one student and all the different rows in the collection would be related to students. What is a relational database (RDB)?

As mentioned, all the data in a database is held in a cluster of similar data (normally similar MEANING not DATATYPE) What is a relation/table? In the above table, all the data would be the type of data you may find in a CUSTOMER table, we have the name, address, etc. Note: not all data is entered, some data may be optional.

Data can be of different formats or data types in a database, some data though may be held but not available to have all actions on them for example, a picture can be added or deleted but not updates (you can not change Esmerelda’s hat for a bonnet etc) it is more common to find the data above held as .........

In the above table we can see that the image has no longer been embedded into the table, instead the location of the image is displayed, this data would be used to locate the image if it is needed but the data itself remains true to the relational principles.

There are various books or papers that discuss databases, and it is often confusing to find that 2 different sets of terms are used, one set RELATIONAL terminology and another SQL terminology. • Relations and datasets are normally displayed or depicted as tables so often the term TABLE is used in SQL rather than RELATION • Tables have columns and rows so most SQL terminology uses these terms • Table = Relation • Column = Attribute • Row = Tuple Database terms

The database is made of tables/relations and relationships. Structure of a database (page 17 of booklet) Student Programme Module 3 tables: student hold the student personal data, programme includes data on the different programme structures and module contains information on the different modules. The tables each hold data that will stand in isolation, if we need info on the BIS programme of the Games programme we look in the programme table but also the tables relate to each other, a student is enrolled on a programme and each programme has a number of modules associated with it and modules may run on a number of different programmes Student Programme Module

It is important that relationships between data are clear and understood in order to get the most out of the database and its data • There are different types of relationships 1 – many Many – Many 1 – 1 Normally 1 – many are the types of relationships that we need to foster Relationships

A company employees a number of people, the personal details such as name, address, salary and payroll number etc are held in the works database. Each employee works for a department and each department is responsible for a number of different projects. What are the main clusters of data (this will give you the tables/relation) What content will be in each of the identified tables/relation (this will give you the columns/attributes within the table/relation) Think about how the different data relates to each other Task (not included in your book so copy into your notes!)

solution Employee department project • Note: When you are designing a database you need to identify the attributes/columns from the existing data or discussions with the client. • An employee works for one department • A department has many employees • A department has many projects • A project is run by one department

In the seminar you are to do Seminar task 1. Before next weeks lecture you are expected to read all the notes in the booklet that relate to this weeks lecture (up to page 17). Next week we are going to look at the tables/relations in more detail, how they work, what additional elements we have to include in addition to the expected attributes and what limitations they have. Next .....

Relational Databases