DATABASES STUDY NOTES
What is a Database?
It is a collection of information related to a particular subject or purpose.
A collection of related data or information grouped together under one logical structure.
A logical collection of related files grouped together by a series of tables as one entity.
Examples of databases.
You can create a database for;
- Customers’ details. - Library records.
- Personal records. - Flight schedules.
- Employees’ records. - A music collection.
- An Address book (or Telephone directory), where each person has the Name, Address, City &
Telephone no.
DATABASE CONCEPTS.
Definition & Background.
A Database is a common data pool, maintained to support the various activities taking place within an
organization.
The manipulation of database contents to yield information is by the user programs.
The database is an organized set of data items that reduces duplications of the stored files.
INTEGRATED FILE SYSTEMS.
These refer to the traditional methods of storing files, i.e., the use of paper files. E.g., Manual & Flat files.
- In Integrated file systems, several inter-independent files are maintained for the different users’
requirements.
- The Integrated file systems have the problems of data duplication.
- In order to carry out any file processing task(s), all the related files have to be processed.
- Some information resulting from several files may not be available, giving the overall state of affairs of
the system.
DATABASE MAINTENANCE.
A Database cannot be created fully at once. Its creation and maintenance is a gradual and continuous
procedure. The creation & the maintenance of databases is under the influence of a set of user programs
known as the Database Management Systems (DBMS).
Through the DBMS, users communicate their requirements to the database using Data Description
Languages (DDL’s) & Data Manipulation Languages (DML’s).
In fact, the DBMS provide an interface between the user’s programs and the contents of the database.
During the creation & subsequent maintenance of the database, the DDL’s & DML’s are used to:
(i). Add new files to the database.
(ii). Incorporate fields onto the existing records in the database.
(iii). Delete the obsolete (outdated) records.
(iv). Carry out adjustments on (or amend) the existing records.
(v). Expand the database capacity, for it to cater for the growth in the volume for enhanced application
requirements.
(vi). Link up all the data items in the database logically.
DATA BASE NOTES Prepared by Mr. Antony Ambia Page - 1 -
, Data Dictionary.
All definitions of elements in the system are described in detail in a Data dictionary.
The elements of the system that are defined are: Dataflow, Processes, and Data stores.
If a database administrator wants to know the definition of a data item name or the content of a particular
dataflow, the information should be available in the dictionary.
Databases are used for several purposes, e.g., in Accounting – used for maintenance of the customer files
within the base.
Database systems are installed & coordinated by a Database Administrator, who has the overall authority to
establish and control data definitions and standards.
Database storage requires a large Direct Access storage (e.g., the disk) maintained on-line.
The database contents should be backed up, after every update or maintenance run, to supplement the
database contents in case of loss. The backup media to be used is chosen by the organization.
Data Bank.
A Data Bank can be defined as a collection of data, usually for several users, and available to several
organizations.
A Data Bank is therefore, a collection of databases.
The Database is organizational, while a Data Bank is multi-organizational in use.
The Database & the Data Bank have similar construction and purpose. The only difference is that, the
term Data Bank is used to describe a larger capacity base, whose contents are mostly of historical
references (i.e., the Data Bank forms the basis for data or information that is usually generated
periodically). On the other hand, the contents of the Database are used frequently to generate
information that influences the decisions of the concerned organization.
TYPES OF DATABASE MODELS.
(1). Relational database model.
A Relational database is a set of data where all the items are related.
The data elements in a Relational database are stored or organized in tables. A Table consists of rows &
columns. Each column represents a Field, while a row represents a Record. The records are grouped
under fields.
~ A Relational database is flexible and easy to understand.
~ A Relational database system, has the ability to quickly find & bring information stored in separate
tables together using queries, forms, & reports. This means that, a data element in any one table can be
related to any piece of data in another table as long as both tables share common data elements.
Examples of Relational database systems;
(i). Microsoft Access.
(ii). FileMaker Pro.
(iii). Approach.
(2). Hierarchical database model.
It is a data structure where the data is organized like a family tree or an organization chart.
In a Hierarchical database, the records are stored in multiple levels. Units further down the system are
subordinate to the ones above.
In other words, the database has branches made up of parent and child records. Each parent record can
have multiple child records, but each child can have only one parent.
Components of Data hierarchy.
DATA BASE NOTES Prepared by Mr. Antony Ambia Page - 2 -
What is a Database?
It is a collection of information related to a particular subject or purpose.
A collection of related data or information grouped together under one logical structure.
A logical collection of related files grouped together by a series of tables as one entity.
Examples of databases.
You can create a database for;
- Customers’ details. - Library records.
- Personal records. - Flight schedules.
- Employees’ records. - A music collection.
- An Address book (or Telephone directory), where each person has the Name, Address, City &
Telephone no.
DATABASE CONCEPTS.
Definition & Background.
A Database is a common data pool, maintained to support the various activities taking place within an
organization.
The manipulation of database contents to yield information is by the user programs.
The database is an organized set of data items that reduces duplications of the stored files.
INTEGRATED FILE SYSTEMS.
These refer to the traditional methods of storing files, i.e., the use of paper files. E.g., Manual & Flat files.
- In Integrated file systems, several inter-independent files are maintained for the different users’
requirements.
- The Integrated file systems have the problems of data duplication.
- In order to carry out any file processing task(s), all the related files have to be processed.
- Some information resulting from several files may not be available, giving the overall state of affairs of
the system.
DATABASE MAINTENANCE.
A Database cannot be created fully at once. Its creation and maintenance is a gradual and continuous
procedure. The creation & the maintenance of databases is under the influence of a set of user programs
known as the Database Management Systems (DBMS).
Through the DBMS, users communicate their requirements to the database using Data Description
Languages (DDL’s) & Data Manipulation Languages (DML’s).
In fact, the DBMS provide an interface between the user’s programs and the contents of the database.
During the creation & subsequent maintenance of the database, the DDL’s & DML’s are used to:
(i). Add new files to the database.
(ii). Incorporate fields onto the existing records in the database.
(iii). Delete the obsolete (outdated) records.
(iv). Carry out adjustments on (or amend) the existing records.
(v). Expand the database capacity, for it to cater for the growth in the volume for enhanced application
requirements.
(vi). Link up all the data items in the database logically.
DATA BASE NOTES Prepared by Mr. Antony Ambia Page - 1 -
, Data Dictionary.
All definitions of elements in the system are described in detail in a Data dictionary.
The elements of the system that are defined are: Dataflow, Processes, and Data stores.
If a database administrator wants to know the definition of a data item name or the content of a particular
dataflow, the information should be available in the dictionary.
Databases are used for several purposes, e.g., in Accounting – used for maintenance of the customer files
within the base.
Database systems are installed & coordinated by a Database Administrator, who has the overall authority to
establish and control data definitions and standards.
Database storage requires a large Direct Access storage (e.g., the disk) maintained on-line.
The database contents should be backed up, after every update or maintenance run, to supplement the
database contents in case of loss. The backup media to be used is chosen by the organization.
Data Bank.
A Data Bank can be defined as a collection of data, usually for several users, and available to several
organizations.
A Data Bank is therefore, a collection of databases.
The Database is organizational, while a Data Bank is multi-organizational in use.
The Database & the Data Bank have similar construction and purpose. The only difference is that, the
term Data Bank is used to describe a larger capacity base, whose contents are mostly of historical
references (i.e., the Data Bank forms the basis for data or information that is usually generated
periodically). On the other hand, the contents of the Database are used frequently to generate
information that influences the decisions of the concerned organization.
TYPES OF DATABASE MODELS.
(1). Relational database model.
A Relational database is a set of data where all the items are related.
The data elements in a Relational database are stored or organized in tables. A Table consists of rows &
columns. Each column represents a Field, while a row represents a Record. The records are grouped
under fields.
~ A Relational database is flexible and easy to understand.
~ A Relational database system, has the ability to quickly find & bring information stored in separate
tables together using queries, forms, & reports. This means that, a data element in any one table can be
related to any piece of data in another table as long as both tables share common data elements.
Examples of Relational database systems;
(i). Microsoft Access.
(ii). FileMaker Pro.
(iii). Approach.
(2). Hierarchical database model.
It is a data structure where the data is organized like a family tree or an organization chart.
In a Hierarchical database, the records are stored in multiple levels. Units further down the system are
subordinate to the ones above.
In other words, the database has branches made up of parent and child records. Each parent record can
have multiple child records, but each child can have only one parent.
Components of Data hierarchy.
DATA BASE NOTES Prepared by Mr. Antony Ambia Page - 2 -
