LU3: Database Systems, Data Warehouses, and Data Mart
Introduction
In today’s competitive business world, efficient use of information is critical
A DBMS (Database Management System) helps organisations manage and optimise data
usage
A database is the foundation of an organisation's information system and decision-making
tools
Poorly designed databases lead to ineffective and inaccurate systems
Databases and DBMS
Database:
A collection of related data, stored in a central location or at multiple locations
Since databases are critical for decision making, it is important to use it as efficiently as
possible
DBMS:
Software that enables data to be created, stored, maintained, and accessed efficiently
Hierarchy of Data:
Level Description
Bit Smallest unit of data
Charact Group of 8 bits (forms a byte)
er
Field Group of characters (e.g., "Cust01")
Record Collection of related fields (e.g., "Cust01, John,
Doe")
File Collection of related records (e.g., Customer
Table)
Databa Collection of related files (e.g., Customer +
se Order tables)
Example (from the two tables):
"Cust01" is a field
"Cust01, John, Doe" is a record
Two rows in the Customer Table = a file
The Customer File and Order File form a database
Accessing the Data in a Database
Data in a database can be accessed in three main ways:
Sequential Access Method
Data is read in the order it was entered
To get to record 9, you must first read records 1–8
Page 1 of 10
, Slower when working with large datasets
Used mostly for data backups
Typically stored on magnetic tape
Random-Access Method
Location of the record does not matter, the record can be accessed in any order
This method is faster than accessing records sequentially
Reused with data stored on magnetic disks
Indexed Sequential Access Method (ISAM)
Combination of sequential and random access
Efficient for both small and large record numbers:
– Random access for smaller record numbers
– Sequential access for larger ones
How it works:
– Each record has an index entry
– Index stores the address of the record
– The index is scanned first, and then the record address is retrieved directly from the
disk
Quick Comparison Table:
Method Access Speed Storage Use Case
Pattern Type
Sequential In order of Slow (on large Magnetic Backup data
entry data) tape
Random Any order Fast Magnetic Operational data
disk
Indexed Uses index + Fast & efficient Disk with Large databases needing both
Seq. address indexing speed and order
The Components of a DBMS
A Database Management System (DBMS) consists of five key components that together
support the efficient management and use of a database
Database Engine
The core of the DBMS
Manages storage, manipulation, and retrieval of data
Interacts with all other DBMS components
Data Definition
Maintains the data dictionary and defines the structure of files in databases
If any changes are made to the database, data definition component is used to make these
changes
Page 2 of 10
Introduction
In today’s competitive business world, efficient use of information is critical
A DBMS (Database Management System) helps organisations manage and optimise data
usage
A database is the foundation of an organisation's information system and decision-making
tools
Poorly designed databases lead to ineffective and inaccurate systems
Databases and DBMS
Database:
A collection of related data, stored in a central location or at multiple locations
Since databases are critical for decision making, it is important to use it as efficiently as
possible
DBMS:
Software that enables data to be created, stored, maintained, and accessed efficiently
Hierarchy of Data:
Level Description
Bit Smallest unit of data
Charact Group of 8 bits (forms a byte)
er
Field Group of characters (e.g., "Cust01")
Record Collection of related fields (e.g., "Cust01, John,
Doe")
File Collection of related records (e.g., Customer
Table)
Databa Collection of related files (e.g., Customer +
se Order tables)
Example (from the two tables):
"Cust01" is a field
"Cust01, John, Doe" is a record
Two rows in the Customer Table = a file
The Customer File and Order File form a database
Accessing the Data in a Database
Data in a database can be accessed in three main ways:
Sequential Access Method
Data is read in the order it was entered
To get to record 9, you must first read records 1–8
Page 1 of 10
, Slower when working with large datasets
Used mostly for data backups
Typically stored on magnetic tape
Random-Access Method
Location of the record does not matter, the record can be accessed in any order
This method is faster than accessing records sequentially
Reused with data stored on magnetic disks
Indexed Sequential Access Method (ISAM)
Combination of sequential and random access
Efficient for both small and large record numbers:
– Random access for smaller record numbers
– Sequential access for larger ones
How it works:
– Each record has an index entry
– Index stores the address of the record
– The index is scanned first, and then the record address is retrieved directly from the
disk
Quick Comparison Table:
Method Access Speed Storage Use Case
Pattern Type
Sequential In order of Slow (on large Magnetic Backup data
entry data) tape
Random Any order Fast Magnetic Operational data
disk
Indexed Uses index + Fast & efficient Disk with Large databases needing both
Seq. address indexing speed and order
The Components of a DBMS
A Database Management System (DBMS) consists of five key components that together
support the efficient management and use of a database
Database Engine
The core of the DBMS
Manages storage, manipulation, and retrieval of data
Interacts with all other DBMS components
Data Definition
Maintains the data dictionary and defines the structure of files in databases
If any changes are made to the database, data definition component is used to make these
changes
Page 2 of 10
