INFORMATION SYSTEMS AND DATABASES

Data and Databases

What is data?

The Latin word datum means ‘something that is known’. The plural of datum is data, which could be translated as ‘things that are known’.

Information may be true or it may be false. It is largely the responsibility of humans to ensure that the information we have contains the truth.

Databases (1)

A database is a large collection of ‘things that are known’. To belong to this collection the ‘things’ require a certain amount of organisation.

You can think of a database as a large collection or store of information (true or false).

An information system is a database along with the means to effectively manipulate the information it contains.

The means to manipulate the information is known as a database management system, usually abbreviated to DBMS.

Databases (2)

Common example of the application of information systems today include automated libraries, airline booking, medical records, video hire, student record keeping, software help, supermarket stock control and countless others

Databases (3)

Computerised information systems offer the following advantages over manual systems of the past: Information stored on CD, DVD, magnetic discs, tapes and flash

drives occupies a relatively small amount of space. Information can be accessed very quickly. The likelihood of human error can be greatly reduced. A computer can deal with what were previously long and

boring tasks performed by humans. Information can be made available to a large number of people

simultaneously, in the one building or around the world. Sophisticated electronic methods can be used to protect the

information in a database.

Components of a database (1)

A very simple type of database is a flat file database.

Flat file databases are managed by programs called file managers. A real restriction with file managers is that they can only deal with the information in one file at a time. They cannot retrieve information that is spread across several files.

The components of this type of database are fields, records and files. A file consists of a collection of records and each record consists of a number of fields.

Components of a database (2)

Field A field in a database is like a small box in which one piece of information of a

particular type is stored. If the database contains information about a small library of books the fields might be: Accession number, Title, Author, Subject.

Record A number of fields make up a record. In the example above each record has

four fields. So each record contains the information for one book.File The complete set of records makes up a file. The flat file can be represented

in table form. The following is a representation of just some of the records:

Acc # Title Author Subject

4171 Programming for Profit Lee, B Programming

4820 The Basics of Memory Management

Hooper, R MS-DOS

5227 Programming with Visual Basic Summers, G Programming

5391 GPFs without Tears Webster, P Windows

5397 Databases Made Easy Hobson, N Databases

Components of a database (3)

Microsoft Word has the facility for creating simple flat file databases to be used for form letters and mailing labels. The database you create can either use a default set of fields or you can customise it with some fields of your choice.

Operating a database

To manage the information in a database a DBMS needs to provide a convenient way of carrying out the following operations:

Data definition involves declaring what fields each record will have and what type of data each will contain.

Data manipulation involves data retrieval, the addition of new records, the deletion of unwanted records and the updating of information in existing records.

Data presentation or display refers to the operations that allow a variety of ways of viewing information. They could include tables, forms, graphics, charts and reports.

Database integrity and security (1)

IntegrityThe term integrity refers to the accuracy or

validity of the data in a database. If database integrity is not maintained, users of the database can never be certain that the information they are obtaining is correct.

Integrity is very important whenever a new record is added, or an existing record is deleted or updated. To some extent it relies on the knowledge, care and honesty of those who are responsible for maintaining the database.

Most database systems have a number of integrity controls that can be used to minimise the possibility of error.

Database integrity and security (2)

Integrity ControlsEach field has a particular data type and only that

type of data can be entered. For example, a field might contain only whole numbers or only text data.

Default values for fields may be used in case of entries that may be overlooked or not known.

Validation rules may be used to ensure an entry is within a given range. Examples: date entry may have to be between two other dates, a weight may have to be less than a certain maximum, a student may be allowed to borrow only three books at a time. These rules may be static (like the three-book limit), or dynamic (may vary according to circumstances).

Mandatory fields may be specified for necessary information.

Database integrity and security (3)

SecuritySecurity involves ensuring that users are allowed to

do the things they are trying to do with a database. Security means protecting a database from destructive

forces and the unwanted actions of unauthorised users, whereas integrity means protecting it from the unwanted or careless actions of authorised users.

Individuals have a right to privacy, so personal information should not be freely disseminated but should be restricted to people who have a legitimate need to know.

In a commercial or industrial environment data is a significant and valuable asset and may require careful protection. Military or national secrets are even more obvious examples of where strict controls might be necessary.

Database integrity and security (4)

The assignment of passwords to users, the use of voice recognition, ID cards.

The granting and revoking of authority for individuals to have access to various parts or views of a database.

The encryption and decryption of particularly sensitive data. The monitoring of database transactions through audits. Strictly adhered-to backup procedures in case of accidental

destruction of files. These procedures would also include .fire drills. to test the effectiveness of the backups.

The installation of a UPS device (uninterruptible power supply) to provide protection against power failures, spikes and surges.

The installation and regular upgrading of an anti-virus program to detect and neutralise the threat of any computer viruses.

Database views (1)

When behind the wheel of a car a driver is given, through the instruments on the dashboard, a view of what is happening inside the motor. The actual movement of oil, the burning of petrol and the motion of thousands of parts is not seen under normal circumstances. The driver is given an external view rather than an internal view. Certain parts of a workshop manual of the vehicle would give the driver another view of the functioning of the motor. In a similar way we can distinguish three views of an information system.

Database views (2)

Internal view An internal view of an information system would allow us to see the

way in which data is actually stored on a disk and the manipulation of bits in memory.

External view The external view is how a user sees the information through the

output devices of the computer. Selected parts of the database are seen through tables, forms,

graphics and reports. This is the view most people have of an information system.

For the small library database an external view may look like this:Computer Studies Library

OVERDUES(on 8 May 04)

Form Class

Student Book

11.1 Birrell, HSmith, W

GPFs Without TearsInside Windows

11.2 McNamara, J Programming for Profit

11.3 Stitters, MVan Haren, A

The Basics of Memory ManagementProgramming with VB

Database views (3)

Conceptual viewA third view, known as the conceptual view, is a

logical view of the way the data items relate to each other. This view is independent of the computer and DBMS being used.

The conceptual view of a relational database is known as the relational schema.

For the small library database the relational schema would look like:

tblBooks = (Acc, Title, Author, Subject)tblStudents = (ID, Family, Given, FormClass)tblLoans = (Acc, Due, ID, Returned op

tblBooks = (Acc, Title, Author, Subject)tblStudents = (ID, Family, Given, FormClass)tblLoans = (Acc, Due, ID, Returned op

The three schema (1)

When two old friends have a conversation there is usually an obvious mutual understanding between them. They are likely to have the same first language, come from similar economic and cultural backgrounds, have many shared experiences, and have many common likes and dislikes. If a common language and a common view of an area of interest exist we say the participants in the communication have the same knowledge domain or Universe of Discourse (UoD).

Human beings, however, have a lot of flexibility when it comes to communication. Sometimes the rules are quite loose. We overstate and understate, we speak with ambiguity, we read between the lines, and we make use of colloquialisms. Today’s information systems cannot tolerate this degree of flexibility. An information system requires a clear unambiguous description of the UoD. The strict set of rules that lay down the boundaries of the UoD is called the conceptual schema.

The three schema (2)

And so, just as there are three distinct views of an information system, there are three schema that describe the rules governing its existence:

Internal schema - rules governing physical storage and manipulation of data.

External schema - rules governing how information is viewed by a user.

Conceptual schema - rules governing the type of information that can be stored and the restrictions on how it can be changed.

Questions and activities (1)

1. What distinction, if any, is there between the terms data and information?

2. Give definitions for the terms:a. Database.b. Information system.c. Database management system (DBMS).

3. What organisations or companies keep information on you in a database?

4. Computerised information systems have a number of advantages over manual information systems. Choose three of these advantages, but counter each by stating an advantage of a manual system.

5. What is the one distinct disadvantage of a flat file database?

Question and activities (2)

10. Create a simple form letter using a flat file database in Microsoft Word:

Choose Mail Merge. from the Tools menu. Create form letters (using the active window). Get data by creating the data source.

Choose the fields you want to use then save your data source. Edit your data source by entering a set of names and addresses. Edit your main document by inserting particular merge fields into a

letter format. Back to Mail Merge. where you can merge the database with your

form letter.

Create a simple form letter using a flat file database in Microsoft

Word:■ Choose Mail Merge. from the Tools menu.■ Create form letters (using the active

window).■ Get data by creating the data source.