Introduction to Computing

© NCC Education LimitedV1.0

Introduction to Computing Unit 3: Information Management


Information Management Unit 3 - 3.2

Review of the Lecture• Databases• Data Modelling• Relational Databases• Data Integrity and Security• Query Language• Data Mining



Databases What is a database?

• A structured store of data• Logically coherent• Designed for a specific purpose• Integrated across an organisation• On a computer system• Based on a model• Allows access to data by all who need it



beans peas tissues

jam tea coffee butter eggs apples

carrots

Data Files Data can be stored in simple files:

• A Serial File- Data is stored one item after another. - e.g. Sales – in the order they happen

• To find an item:- Start at the beginning- Visit each item in turn- Until found or end of file

- Finding an item can take a long time



Stock no. 12

Stock no. 15

Stock no. 17

Stock no. 19

Stock no. 20

Stock no. 25

Stock no. 56

Stock no. 67

Stock no. 78

Stock no. 87

Data Files• A Sequential File

- data is stored one item after another in some order- E.g. Sales – in stock number order

- To find an item:• start at the beginning• visit each item in turn• until found or stock number higher than the one

searched for

- Finding an item can be quicker:• can stop the search early if item not present• or…. can use an index and fast forward to the right place



Data Files Adding new data to simple files:

• Serial- go to end of file – add new item

• Sequential- start at the beginningwrite old data to new file until correct position for

new item- write new item to new file- write the rest of old file to new file



Data Files

Direct Access• This method calculates the correct

position and places the data item there. It finds data in the same way.



Data Files

Direct Access• A very quick method• It requires a random access storage

device such as a disk• Cannot use tape storage



Problems with Simple Data Files Simple data files can be awkward for an organisation.

What if……• Two or more people need to update the same

file?• The software is updated?• The data structure needs to be changed?



Data Redundancy• The same data may get stored more

than once• One copy gets updated• The other does not

ErrorsLack of data integrity



Data Dependence

What if the organisation’s data storage needs change?

There is a need for:• Updated data structure• Updated software



The Database Approach• Data is stored in an integrated

database• Data is stored centrally• The organisation can control it• Everyone has access to the same data• Data is not spread around lots of files• Data can have multiple views



The Database Approach• Reduced data redundancy• Data is consistent• Data is shared• Corporate standards can be enforced• Better security• Controlled access• Leads to data integrity



Keeping Data Safe

Security• Data is protected against loss or

unauthorised access

Integrity• Data is as it should be – complete,

consistent and correct



Data Independence Simple Filing Systems:

• The software must “know about” the way that the data is organised

• Changes to the data structure require changes to the software

Databases• Separate the data from the applications• The data is under the control of a database

management system (DBMS)



DBMS

A set of programs:• for defining a database• for creating a database• maintaining a database• manipulating a database

- (queries, reports, updating)



application

DBMS

data

DBMS• A Database Management System

manages the physical data.• Applications can be produced that

work on the data through the DBMS.



DBMS The DBMS:

• Can enforce rules to ensure integrity.• Can separate the application from the

data.• Can allow changes to the applications.• Can perform validation checks.• Provides security features.



Hierarchical Model

Data Models - Hierarchical•Data must be structured for ease

of processing.

•The structure is known as the data model or schema.

•The description of the model is stored in the data dictionary.

•There are various models, e.g. the hierarchical model. This works in some cases



Entities

Field name ValueFname BarackSname ObamaOccupation President

•An entity is a real-world object.

•We store data about entities.

•The entity has attributes.

•Each attribute makes up a data field.

•Data about one entity makes up a record.

1 record



Data Models - Relational• The most common model is relational.

- Based on interconnected tables- Each table is made of rows and columns.- A row corresponds to a record.- Each row of a table must have the same

structure.- A column corresponds to a field.- Tables are linked by keys.



Entity Relations A relational database separates the data about different entities into different tables.• A customer can place many

orders. • Each order can contain many

items.



Tables

Links

Relational Model



Field namestudent_numbersurnameforenamedate_of_birth

Field nameroom_numberdatecustomer_idextras

table: student table: hotel_booking

compound primary key

simple primary key

Key Fields• Each table has a primary key.• This uniquely identifies each record.• It may be one field such as an id number.• It may be a compound key.



Links

A primary key links to a foreign key in a different table.

Au_ID is primary key here

Au_ID is foreign key here



Integrity and Security• The data is held centrally.• Centralised back up • Levels of access• Validation enforces rules on data entry.• Record locking prevents inconsistent

updates.• Referential integrity prevents

conflicting updates.



Validation•A check that data is acceptable.•Carried out by the software at the time of data entry

•Does not ensure that data is accurate

Examples:length check data item is not too longrange check data is within a limited rangepresence check data must be enteredcheck digit an extra digit is calculated by an algorithm

and added to the datatype check data is the correct data type



Querying a Database• Databases can get big.• We need a way to extract just the data

we need.• Often done using a query language.• DBMS may have QBE (query by

example).• There are many examples of query

languages.



Querying a Database Some DBMS programs allow Query by example (QBE).

This query selects records where the number of items in stock is more than 400.



Querying a DatabaseThe same query can be constructed in a query language such as

SQL:

SELECT stock.stock_number, stock.stock_name, stock.number_in_stock, supplier.supplier_name, supplier.supplier_telephoneFROM stock INNER JOIN supplier ON stock.supplier_number = supplier.supplier_numberWHERE (((stock.number_in_stock)>400))ORDER BY stock.number_in_stock;

The result of running the query is:



Creating a Database The query language can also create databases:

CREATE SCHEMA SCHOOL CREATE TABLE STAFF(FName VARCHAR(15) NOT NULL, LName VARCHAR(15) NOT NULL, SocSecNo INT NOT NULL, StaffNum INT NOT NULL, Title VARCHAR(10), Code CHAR(5), PRIMARY KEY (SocSecNo), UNIQUE (StaffNum), FOREIGN KEY (Code) REFERENCES DEPARTMENT (DeptCode));



Nowadays there is a huge amount of data in databases. There may be useful information that was not part of the plan when the database was set up.

For example, a supermarket with a loyalty card scheme records every purchase made by each customer.

Data Mining



Data Mining• The supermarket knows the names and

addresses of its card holders.• It knows what they have bought.• It can look through the data for patterns.• Maybe people in certain areas tend to

buy certain things.• Advertising can now be targeted.



Data Mining• Similar items are grouped together.• Attempts to find a model

• Data mining:- uncovers patterns- discovers new relationships- can help to make predictions



Data Mining

Uses:• Market analysis• Combating terrorism• Predicting genetic disorders• Predicting drug reactions• Traffic analysis



Government

Criminals Insurance companies

Security services

Tax authorities

Friends and family

Data and Confidentiality With so much data being stored and easy to copy, people worry about who has access to it.



Data and Confidentiality Most countries have data protection laws.

These are designed to protect privacy.



Data and Confidentiality Most data protection laws are similar:

• Data may only be used for the specific purposes for which it was collected.

• Data must not be disclosed to other parties without consent. • Personal information may be kept for no longer than is

necessary.• Personal information may not be transmitted outside a particular

area. • Those holding personal information are required to have

adequate security measures in place. • Subjects have the right to have factually incorrect information

corrected.

…..but it is so easy to copy data, can these laws be enforced?



Unit 3

Any questions?

Introduction to Computing

Documents

data item

data filesadding new

physical data

applicationsthe data

data redundancythe

beginningwrite old data

data filesdirect accessa

organisations data storage