The document defines key concepts related to databases including: - A database is a collection of related data organized for easy access and manipulation. - Databases have properties like representing aspects of the real world and containing related information built and populated with data. - Advantages include reducing data redundancy, sharing data, ensuring data integrity and security, and resolving conflicts. - There are two types of data independence: physical independence provides flexibility in file organization and storage without changing conceptual views, while logical independence provides flexibility to change conceptual schemas without changing external schemas.

1. LBEF
BA
TCH
2012
What is database?
A database is a collection of related data. A data item is a smallest named unit of data.
What are the properties of database?
 Aspects of real world
 Related information
 Built, design, and populated with data
 Consists of users and application
What are the advantages of database?
 Reduction of redundancy
 Sharing data
 Data integrity
 Data security
 Conflict resolution
 Generate standard records or specific records
Data independence
In database system, there are two types of data independence, they are
i. Physical data independence
ii. Logical data independence
Physical data independence: It provides flexibility for organizing the files at physical level or
changing the physical storage devices without changing the conceptual view or any external level.
Logical data independence: it provides the flexibility to change the conceptual schema without
changing the external schema. It is difficult to achieve logical data independence compare to
physical data independence, because application programs are heavily dependent on the logical
structure of the data they access.
Data modeling
Data modeling refers to on what type of data should be stored on the database and how to process the
data.

2. LBEF
BA
TCH
2012
Entities
Entities are the main data objects through which we can collect information. Any occurrence of an entity
is called an entity instance. Entities are written inside rectangle boxes.
Attributes
Attributes are the behaviors of entities which provide detailed information about them. Key attribute is
used to identify a unique instance of an entity. Attributes are written circle.
Relationships
A relationship represents the association between one or more entities. Types of relationship are one-
to-one, many-to-one, one-to-many and many-to-many. Relationship name is written inside the
diamond.
Disadvantages of database system
 Initial installment is high
 Training is required
 Unauthorized access
 Complex recovery