Database Management System (DBMS)

Advantages

Disadvantages

1) Primary Key

A primary key is an attribute which uniquely identifies each record within a table. It cannot accept null values. We can have only one primary key in a table.

2) Alternate Key

It is a column or a group of columns in a table that uniquely identifies every row in that table. All the remaining candidate keys which are not selected as a primary key are called alternate keys.

3) Candidate Key

A candidate key is a minimal super key which contains no extra attributes. It is also called a subset of a super key. It is a set of attributes that uniquely identify records in a table.

Data Definition Language (DDL)

Database designers use Data Definition Language (DDL) to define the structure of a database. DDL refers to the set of SQL commands that can create and manipulate the structure of a database. Common DDL statements are:

Data Manipulation Language (DML)

Once a database completes defining the structure of a database (database schema), the database is ready for the entry and manipulation of data. Data Manipulation Language statements are used for managing data in a database.

Data Control Language (DCL)

The DCL component of the SQL language is used to create privileges to allow users access to, and manipulation of, the database. There are two main commands:

a) Hierarchical Model

As its name implies, the hierarchical database model defines hierarchically-arranged data. A hierarchical database consists of a collection of records which are connected to one another through links. A link is an association between precisely two records.

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b) Network Model

A network database is a type of database model where multiple member records or files can be linked to multiple owner files and vice-versa.

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c) Relational Database Model

A relational database is a collective set of multiple data sets organized by tables, records, and columns. RDBMS establish a well-defined relationship between database tables.

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1) 1NF (First Normal Form)

Once we have un-normalized data sets, we arrange them in First Normal Form by making each attribute atomic, which means in 1NF there should not be repeating data groups.

2) 2NF (Second Normal Form)

After arranging the given data set in 1NF, we eliminate functional dependency attributes. In this case, subject depends upon the teacher, not age and address. Similarly, age and address also depend on the teacher, not the subject. So, in 2NF, we remove such functional dependencies by introducing a primary key and foreign key.

Teacher Table:

Subject Table:

3) 3NF (Third Normal Form)

As we normalize till 2NF, now to achieve 3NF we have to overcome some more issues associated with 2NF. Let’s say in the table below, if one teacher left the job, data in this table and functional dependencies are eliminated, it will not affect.

But in the table below, if a teacher is changed, it will affect. A change in one affecting another is known as transitive functional dependency.

So, to prevent loss of information due to transitive functional dependencies, we assign a separate subject code for each subject, so that even a change in the teacher does not affect the subject.

Advantages

Disadvantages

Advantages

Disadvantages