In other words we can said that ER-Diagram is the blue print of Database.

ER-Diagram is the graphical representation of Data. ER-Diagram stands for Entity-Relationship Diagram.

Entity - Entity means any thing which are exist in the real world is known as entity. eg --> book, pen, chair, laptop, etc.

In SQL there are two type of entity

1. Physical entity

2. Conceptual entity

Physical entity - Physical entity are those entity which physically exist in the real world is know as physical entity. It is also known as Tangible entity.

Conceptual entity - Conceptual entity are those entity which doesn't exist physically in the real world is known as conceptual entity. It is also known as Intangible entity.

In DBMS both entities are represented by Rectangle.

Attribute - Every entities describe the property and that property is known as attribute.

In SQL there are six types of attributes.

1. Simple attribute.

2. Composite attribute.

3. Single-valued attribute.

4. Multi-valued attribute.

5. Key attribute.

6. Derived attribute.

Simple attribute - An attribute which are not divided further is know as Simple attribute. eg --> Id, age , email and so on.

Composite attribute - An attribute which can be further divided is known as Composite attribute. eg --> name , address , DOB and so on.

Single-valued attribute - An attribute which contain single value is known as Single-valued attribute. ex --> age , id etc.

Single-valued attribute represented by ellipse.

Multi-valued attribute - An attribute which contain multiple values is known as multi-valued attribute. ex --> name, email, etc.

Multi-valued attribute is represented by double ellipse.

Derived attribute - Any attribute which derived from other attribute is known as Derived attribute. It is represented by dotted/ellipse.

eg --> Age attribute can be derived from DOB attribute so, here we can said that age attribute is an derived attribute.

Key attribute - Key attribute are those attribute which can be uniquely identified. It is represented by Underline.

eg --> In a company multiple employee work to identify the employee company gives employee id to each employee that must be unique.

As we know that there are many attributes present in SQL and we also know about the meaning of entity and it's types.

Know we know about the meaning of Relationship and it's types in SQL.

Relationship - Association among two entities are known as "Relationship".

In SQL there are four types of relationship.

1. One to one relationship.

2. One to Many relationship.

3. Many to one relationship.

4. Many to Many relationship.

One to one relationship - Department and HOD entities have one to one relationship i.e. for one department we will have only one HOD.

One to Many relationship - Company and Employee have one to many relationship i.e. in one company many employee work.

Many to One relationship - Employee and Company have many to one relationship i.e. Many employee can work under one company.

Many to Many relationship - Product and Customer entities contains many to many relationship, we need to identify the many to many relationship by check in both the directions i.e., we need to get one to many relationship in each direction like one product can be purchased by multiple customers and one customer can purchase multiple products hence we can conclude that product and customer has many to many relationship.

HTML stands for Hyper Text Markup Language. It is a standard markup language for creating web pages and web applications. It is the foundation of the Worl Wide Web and is used to describe the structure of the content in documents, such as heading <h1>, paragraph<p></p>, list and other show items.

In HTML tags, elements and attributes are very important things. With the help of these, we can make HTML pages. Don't worry we know these things one by one. First, we know about tags then elements and then attributes.

What are tags in HTML?

Html tags are like keywords that determine how web browsers display the content on the screen. Paragraph tag <p></p>, and heading tag<h1><h1> are examples of HTML tags. There are so many tags present in the HTML so, we know one by one tag later.HTML tags contain three main parts: an opening tag, content and a closing tag. But some HTML tags are unclosed.

Some points to remember about tags are as follows -->

• All HTML tags must be enclosed within < > these brackets.

• Every tag in HTML performs different tasks.

• If you have used an open tag <tag>, then you must use a close tag </tag> (except some tags)

Syntax

<tag> content </tag>

Note- HTML tags are always written in lowercase letters.

HTML tags examples.

What are HTML elements?

An HTML file is made of elements. These elements are responsible for creating web pages and defines content in that webpage. An element in HTML usually consists of a start tag <tag name>, close tag </tag name> and content inserted between them. Technically, an element is a collection of start tag, attributes, end tag, content between them.

Note- Some elements does not have end tag and content, these elements are termed as empty elements or self-closing element or void elements.

What are HTML Attributes?

• HTML attributes are special words which provide additional information about the elements or attributes are the modifier of the HTML element.

• Each element or tag can have attributes, which defines the behaviour of that element.

• Attributes should always be applied with start tag.

• The Attribute should always be applied with its name and value pair.

• The Attributes name and values are case sensitive, and it is recommended by W3C that it should be written in Lowercase only.

• You can add multiple attributes in one HTML element, but need to give space between two attributes.

Syntax

<element attribute_name="value"\>content</element>

Example

1. <!DOCTYPE html\>

2. <html>

3. <head>

4. </head>

5. <body>

6. <h1> This is Style attribute</h1>

7. <p style="height: 50px; color: blue"\>It will add style property in element</p>

8. <p style="color: red"\>It will change the color of content</p>

9. </body>

10. </html>

output:

1. <p  style="height: 50px; color: blue">It will add style property in element</p> In the above statement, we have used paragraph tags in which we have applied style attribute. This attribute is used for applying CSS property on any HTML element. It provides height to paragraph element of 50px and turns it colour to blue.

2. <p  style="color: red">It will change the color of content</p>

In the above statement we have again used style attribute in paragraph tag, which turns its colour red.

In next article we know about different type of an HTML tags.