DATABASE MANAGEMENT SYSTEM

Database Management System (DBMS) is a set of programs that enables you to store, modify, and extract information from a database, it also provides users with tools to add, delete, access, modify, and analyze data stored in one location.

What is Database?

A database is a structured collection of data. The data are typically organized to model relevant aspects of reality (for example, the availability of rooms in hotels), in a way that supports processes requiring this information (for example, finding a hotel with vacancies).

How can we design a database?

Database design is the process of determining the content and arrangement of data and is a two step process. In the first step, user requirements are gathered together and a database is designed which meets these requirements as closely as possible. The second step consists of transforming this information level design into a design for the specific DBMS which will be used to implement the system.

What is ER-Modeling?

Entity Relationship Modeling (ER-Modeling) is the most common way to express the analytical result of an early stage in the construction of a new database.

 What is ER Diagram?

Entity relationship diagrams are a way to represent the structure and layout of a database. It is often used as a way to visualize a relational database.

Symbols used in E-R Diagram

• Entity – rectangle
• Attribute – oval
• Relationship – diamond
• Link - line

What is Entity?

Entities are the principal data object about which information is to be collected.. Entities are usually recognizable concepts, either concrete or abstract, such as person, places, things or events which are relevance to database.

What is Attributes?

Attributes described the entity of which they are associated. For example: “Dilip Saha” is one instance of the attribute NAME.

What is Primary Key?

A primary key is a table column that can be used to uniquely identify every row of the table. Any column that has this property will do -- these columns are called candidate keys. A table can have many candidate keys but only one primary key. The primary key cannot be null.

What is Foreign Key?

A foreign key is a column, or combination of columns, that contain values that are found in the primary key of some table (including, possibly, itself). A foreign key may be null, and almost always is not unique.

What is Composite Key?

A composite key is a combination of two or more columns in a table that can be used to uniquely identify each row in the table. Uniqueness is only guaranteed when the columns are combined; when taken individually the columns do not guarantee uniqueness.

Rectangle -- Entity

Ellipses -- Attribute 

Double ellipses -- multi-valued attribute

Dashed ellipses-- derived attribute, e.g. age is derivable from birth date and current date

What is Relationships?

Relationship represents an association between two or more entities. For example: “students majors in departments”, here we have two entities viz, “student” and “department”. The relationship is “majors in”.

Normalization:

Definition: Normalization is a technique that is widely used as a guide in designing relational databases. It is essentially a two-step process that puts data into tabular form by removing repeating groups and then removes duplicated data from the relational tables. In other word it is typically a refinement process after the initial exercise of identifying the data objects that should be in the database. Some types of normal forms are defined bellow:

          First Normal Form: A relation or table is said to be first normal form (1NF) if it does not contain repeating groups.

          Second Normal Form: A relation is said to be in second normal form (2NF) if it is in first form and no non-key attributes is functionally dependent on only a portion of the primary key.

          Third Normal Form: A relation is said to be in third normal form (3NF) if it is in second form and if the only determinants it has are candidate keys.

          Fourth Normal Form: A relation is said to be in fourth normal form (4NF) if it is in third form and the relation has no multi valued dependencies.