Database Management Systems (DBMS)

Data Handling Software

Paper Databases

• A database is a collection of data or information which is held together in an organised or logical way.

• Databases can either be paper based or computerised.

Computerised Databases• You will come across

computerised databases in every aspect of your life.

• Here are some examples with which you will be familiar:– Search engines e.g. Google,

Ask, Bing – School electronic registers – Library database – Shop stock control system – DVLC - stores details of all

driver licences and car registrations

Specification

• Candidates should be able to define a database as a large collection of data items and links between them, structured in such a way that allows it to be accessed by a number of different applications programs.

What You Need to Learn From This Lesson

• Definition of a database• Advantages and disadvantages of a database approach over

flat files • Database security • Hierarchy of passwords• Storage of data separate to programs

Key Words

• Fields• Table• Primary Key• Record• Relational Database Management System (RDMS)• Query • Report

Fields

Field Names

Table

Primary Key

Definition of files, records and fields• A file

– is a set of related records• e.g. a file of patients

• A record – is a collection of data about a particular person, object or

concept• e.g. the data about one patient

• A field– is a subdivision of a record which holds a particular item

of data with a given data type• e.g. • Medicine quantity (data type is number)• Patient name (data type is text)

• Primary Key– field(s) to uniquely identify a record

Records

Primary Key

A TABLE is made up of RECORDS

RECORDS are made up of FIELDS

FIELDS are made up of CHARACTERS

Stock code: SP2544

Stock name: Timber door panel

Material: Pine

Size: 600x600mm

Quantity: 25

File, records & fields

Stock code: RF4237

Stock name: Timber door panel

Material: Pine

Size: 600x600mm

Quantity: 25

Stock code: PY3746

Stock name: Timber door panel

Material: Pine

Size: 600x600mm

Quantity: 25

Stock code: TM1253

Stock name: Timber door panel

Material: Pine

Size: 600x600mm

Quantity: 25

Stock File

One stock record

One field

Databases &Database management software (DBMS)

• A database is a collection – of tables and records

• DBMS - database (management) software – Is a layer of software inserted between the different

applications (programs) and this data.– It is responsible for the

creation/maintenance/manipulation of the database

Flat File Databases

• A flat-file database is a simple database that stores all data in a single table in one file

• A flat-file database can be stored in a text file, such as a a Spreadsheet, or in a database file that contains one or more unrelated tables.

Flat File Advantages

• Useful for simple lists:• Easy to create

Flat File Disadvantages

•Large amounts of duplicated data•Difficult to update• If entries change all instances have to be updated

•Security•All users have access to the same set of data

Relational Databases• The problems associated with flat files can be

solved by moving some of the data out of the main table and accessing it when required

• holds data in many tables of records which are linked by relationships.

• A relationship is implemented throughcommon fields held in the two tables

What's the problem?

• Avoids data duplication (redundancy)– data stored once– linked by key fields– all data available via relational links in key fields

• Ensures consistency of data of data to all users

Relational Database Advantages

Relational Database Advantages continued

• Increased security - What makes databases secure?– Hierarchy of passwords– ID– Authentication– Authorisation to files and processing– DBMS can check permissions Read only Write only etc.

Users only allowed to view the data they are entitled to, so there is less risk of accidental or deliberate destruction.

• Data integrity– It is possible to specify constraints on the data to ensure it

is in the correct format and range.

Disadvantages of relational database vs. flat files

– More complicated to design and create a relational database than a flat file system

– More expensive because flat file system can by created simply using spreadsheet software where as a relational database needs to be created with a DBMS

Database Security

– DBMS controls security access to different parts of the database

– Each user is given appropriate access rights to the database appropriate to the type of user they are and their job

Database Software

Advantages/disadvantages of Database Software

Advantages of Relational Databases Disadvantages of Relational Databases

Only have to enter data once They are complex, difficult, and time-consuming to design

Files and tables are linked, and so means if the data is changed in one application, the rest of the database will automatically be updated for other applications

Damage to database affects virtually all of the application programmes

It is quick and easy to access informationSearch criteria can be use, saved and modified

Initial training for programmers and users is needed and can be costly

Everyone uses the same data, and so the data is consistent

Validation checks can be performedEnsures data integrity

The structure of the database can easily be changed

Database Software

• A database is an organised collection of data or information. • Computerised databases can import or export information. • This needs to be done easily as different systems are often

used and the data must be read the same each time.

Query

• The whole point in storing data in a database is the fact that it is easy to perform searches to extract data.

• One way of searching for that data would be performing a search using the tables in the database.

• Another is using commands written in a language called Structured Query Language (SQL).

Reports

• Databases can perform queries and produce the results in a report.

• This is usually printed out and presented in such a way that it is easily understood – for e.g. graphs, charts, tables, etc.