Use of ICT in Data Management

AS Applied ICT

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Processing a record

Sequential Files

Functions in a Sequential File

Index Sequential and Random Access File

Database Management System

Contents

Performing Functions

Hierarchical Database Management System

Network Database Management System

Relational Database System

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What is a database?It is a collection of related data.It consists of records and fields; each

record contains the same set of fields.One field contains one piece of

information.What is the purpose of DBMS?

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Database Management System (DBMS)

This is a kind of software that is used to manage database systems:– Structure of individual data files– Relationships between data items + between

data files– How data is searched (interrogated)– Properties of the database (queries, updating or

amendments)

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Sequential Files• Records are stored one after the other in the

order they were added to the storage medium. • Storage Medium: Magnetic Tape• Two ways in which records can be arranged:1. Have the records in an order using a key field.What is a key field?Its is unique for every record. It is required to ensure

that you don’t have any duplicates.

This type of type of sequential is called ordered sequential.

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Sequential Files

2. Another way is to arrange the records in no particular order

This is type of sequential is called unordered sequential.

Another name for an unordered file is serial file.

There is only one way of accessing the data: by going through each record one by one.

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Sequential Files

• Ordered file -- > data is put in order of a key field (For example: customer ID)

• Unordered file -- > as the name suggests as the data in no particular order.

Disadvantages of using sequential files

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Disadvantages of a Sequential File

1. You can only add a new record at the end of the file

2. If a record needs to be replaced it must be the EXACT same length as the original

3. A record can only be updated if the data item used to replace the existing data is the same length as the original.

4. Processing of a sequential file is slower compared to other files. How?

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How do you process records?

• You need to read through each and every record until you get the one you want.

• Only recommended for applications where most/all the records are to be processed at one time.

For example: British Gas sends out bills to all their customers. You receive a bill after every three months. So a person who joins in January will receive their bill in April along with all the other people who also joined in January.

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Functions in a Sequential File

Adding records -- > easy Amending + Deleting -- > not so easy. If it is an unordered sequential file amending

and deleting are fairly difficult If it is an ordered sequential file amending

and deleting are sort of easy. This is done with the assistance of a transaction file.

What is a transaction file?It contains the actions to be carried out on the records.

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Performing Functions in an Ordered File

The key field is used.Master File

ID Name Gender

1 Mr Ahmed Male

2 Mrs Russell Female

3 Mr Royale Male

4 Mr O’Neil Male

Transaction File

ID Trans. Name Gender

1 D Mr Ahmed Male

2 C Mr Russell Male

3 D Mr Royale Male

5 A Hafiz Male

New Master File

ID Name Gender

2 Mr Russell Male

4 Mr O’Neil Male

5 Hafiz Male

Computer reads the first record from the transaction and the master file. If the ID doesn’t

match (In this case it does), the computer writes it to the new

master file

The next record is then read and the

transaction is carried out by the

computer

D: DeleteC: ChangeA: Add

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Indexed Sequential and Random Access Files

• These are stored in order• As opposed to the sequential files that were

stored on magnetic tape, index sequential are stored on a disk, allowing them to have direct access.

• Each record has a fixed field length.• Having things ordered provides a greater

speed of access.

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Indexed Sequential and Random Access Files

• Indexed sequential -- > records are in an order (for example: by surname)

• Index: pointer to where on the disk the record is stored. The table may be from A-Z, the index can then point out where all the A’s are, where all the B’s are, etc. it works like the index of a book.

• If you search for something starting with ‘S’. All the records from A to R will be ignored. Then every record in the ‘S’ section is read one by one until what you get what you need.

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Indexed Sequential and Random Access Files

• Banks use sequential access systems in order to process cheques. This will be very useful especially in online banking.

• Index sequential files are used with hybrid batch processing systems- employee records.

• This allows for direct access when an individuals record needs to be seen.

• Records held sequentially allowing serial access when producing a payroll.

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Indexed Sequential and Random Access Files

• Random Access -- > quickest form of access.• Despite the position of the desired record, it

will take the same amount of time to access it.• Each record has a key; the computer looks up

the key -- > goes to the appropriate place on the disk to access it.

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Hierarchical Database Management Systems (DMS)

• No longer used. Why?One-way relationship problem!• A hierarchical DMS -- > family tree like structure.• One mother can have many children, but the

children can have only one mother.’• Windows system several users each user will

have several documents• Enabling fast access to data

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Network Database Management System (DMS)

• Overcome the faults of the hierarchical DMS• Many organisations now use a distributed

database system.• Data is stored on computers that are then

linked by a LAN/WAN.• Data in the database is duplicated several times,

so it is unlikely to loose the data and it also gives the users faster access times.

• To a user it seems to be a single system

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Network Database Management System (DMS)

• System caters for complex searches; search is not necessarily done at the site where the user is.

• For example: something that is done in Dukhan on our computers could be then processed in Doha.

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Network Database Management System (DMS)

• Another type of Network DB stored on one device– accessed from a number of network locations.

• Users access the database – but don’t slow the system down.

• For example: PNC (Police National Computer) and DVLA (Driver and Vehicle Licensing Authority)

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Relational Database Systems

What is a relational database?It consists of separate tables that are all related

in some way. So this means that each table needs to have a key field that is a field in another table. So what?

The data from the initial table can then be combined with data from another table when you need to produce reports.

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Relational Database Systems

Customer

Customer ID

Name:

Date of Birth:

Address:

Telephone Number:

DVD

DVD ID

Name of DVD:

Number of Copies:

Main Actor:

Customer ID

In this table the Customer ID is the Key Field

In this table the DVD ID is the primary key. The Customer ID is the foreign key. These two tables are linked by the Customer ID.

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Relational Database Systems

• Standard Programming Language dealing with relational tables is called Structured Query Language (SQL). What is it used for?

It is used for queries and producing reports.Advantages of relational databases

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Advantages of Relational Databases

1. Data not repeated – storage capacity not wasted. Comparing this to a flat file database, in which data is repeated.

2. Data retrieval is quicker. If the data is repeated, hackers will have greater ease in accessing the data. Relational databases reduce this risk.

3. They also allow room for expansion