Prof. A database is a structure that contains information about many different categories of information and about the relationships between those categories (Pratt & Adamsk 2010). Database objects are entities that exist within a database to support operations such as storing, retrieving and manipulating data. Organizations use large amounts of data and database management system to store and transform data into information to support making decisions. A database management system consists of the following three elements:
1. The physical database: the collection of files that contain the data.
2. The database engine: the software that makes it possible to access and modify the contents of the database.
3. The database scheme: the specifications of the logical structure of the data stored in the database.
As we know, database is structured collection of data; computer based databases are usually organized into one or more tables. A table stores data in a format similar to a published table and consists of a series of rows and columns.
In a database model, each object that we want to track in the database is known as entitiy. For example, in a college database there might be several entities which is known as set of similar objects. Some of the entities in college database are:
Attributes describes one aspect of an entity type. Entity type is described by set of attributes. An entity is a real-world item or concept that exists on its own (Shiflet, 2002). The set of all possible values for an entity is the entity type. Each entity has attributes, or particular properties that describe the entity. For example student Indra Paudel has properties of his own studentID, StudentName and StudentGrade.
Figure 1 E-R Diagram notation for an attribute domain ( StudentGrade ) of an entity type (Student).
Let’s have a close look of
References: Pratt, P.J, & Adamski J.J, (2011). Concepts of Database Management. Ohio, OH: CENGAGE Learning. Shiflet, A.b, (2002). Entity Relationship-Model. Retrieved from http://wofford-ecs.org/dataandvisualization/ermodel/material.htm