CHAPTER TWO

DATABASES

2.4.5. QUERYING

Data base query is one of the most important features of databases. Query is a strategy used by database managers to ask questions and get answers from the database. For instance, a school database manager, can query the school database to find out the number of students that registered for a particular subject. The result of the query will be displayed from the database.

2.4.6. REPORT

A report is the document displayed by the database after the database has been queried.  For instance,
the list of registered students displayed is a report.

2.5. TYPES OF DATABASE

Basically, there are three types of databases, namely:- 

2.5.1. Flat file database
2.5.2. Hierarchical database
2.5.3. Relational database

2.5.1. FLAT FILE DATABASE

A database file that consists of a single data table is called flat-file database or sequential file. It is used to maintain simple records, e.g. file containing list of students etc.

2.5.2. HIERARCHICAL DATABASE

Hierarchical Database is the type of database whereby the data are arranged in a hierarchical pattern. Hierarchical database can be visualized as the pedigree of a family, consisting of the parents, and grandchildren.

2.5.3. RELATIONAL DATABASE

Relational Database is a database that consists of more than one table. Such tables can be linked together to share information or data they contained.  For example a database "student" is created having two tables "Registered Students" and "Examination Results" as shown in figure below.

Copyright2015@Digital Vision Digital content Development Center.

www.digitalvision.net.ng