Entity Relationship (ER) Diagram Model

Weak Entity

A __________ is a type of entity which doesn't have its key attribute. It can be identified uniquely by considering the primary key of another entity. For that, weak entity sets need to have participation.

Simple attribute

A type of attribute that can't be divided any further. For example, a student's contact number. It is also called an atomic value.

Composite attribute

A type of attribute where breaking down attributes is possible. For example, a student's full name may be further divided into first name, second name, and last name.

Entity set

An _______ is a group of similar kind of entities. It may contain entities with attribute sharing similar values. Entities are represented by their properties, which also called attributes. All attributes have their separate values. For example, a student entity may have a name, age, class, as attributes.

Relation

Association between the instances of one or more entity types

- Eliminate any redundant entities or relationships - You need to make sure that all your entities and relationships are properly labeled - There may be various valid approaches to an ER diagram. You need to make sure that the ER diagram supports all the data you need to store - You should assure that each entity only appears a single time in the ER diagram - Name every relationship, entity, and attribute are represented on your diagram - Never connect relationships to each other - You should use colors to highlight important portions of the ER diagram

Best Practices for Developing Effective ER Diagrams

Entity

Can be a person, place, object, event or concept about which data is to be maintained. The characteristics of _____ are must have an attribute, and a unique key. It is made up of some 'attributes' which represent that entity.

Cardinality

Defines the numerical attributes of the relationship between two entities or entity sets.

1. One-to-One Relationships 2. One-to-Many Relationships 3. May to One Relationships 4. Many-to-Many Relationships

Different types of cardinal relationships are: (4)

Peter Chen, 1971

ER diagrams are visual tools that are helpful to represent the ER model. ___________ proposed ER Diagram in _______ to create a uniform convention that can be used for relational databases and networks. He aimed to use an ER model as a conceptual modeling approach.

- rectangle - oval - diamond

Entity Relationship Diagram Symbols & Notations mainly contains three basic symbols which are ________, _________ and _______ to represent relationships between elements, entities and attributes.

- ER model allows you to draw Database Design - It is an easy to use graphical tool for modeling data - Widely used in Database Design - It is a GUI representation of the logical structure of a Database - It helps you to identifies the entities which exist in a system and the relationships between those entities

Facts about ER Diagram Model (5)

- Rectangles - Ellipses - Diamonds - Lines - Primary key - Double Ellipses

Give the main components and its symbols in ER Diagrams:

Many-to-One

More than one entity from entity set X can be associated with at most one entity of entity set Y. However, an entity from entity set Y may or may not be associated with more than one entity from entity set X.

Many-to-Many

One entity from X can be associated with more than one entity from Y and vice versa.

One-to-one

One entity from entity set X can be associated with at most one entity of entity set Y and vice versa.

One-to-many

One entity from entity set X can be associated with multiple entities of entity set Y, but an entity from entity set Y can be associated with at least one entity.

- Helps you to define terms related to entity relationship modeling - Provide a preview of how all your tables should connect, what fields are going to be on each table - Helps to describe entities, attributes, relationships - ER diagrams are translatable into relational tables which allows you to build databases quickly - ER diagrams can be used by database designers as a blueprint for implementing data in specific software applications - The database designer gains a better understanding of the information to be contained in the database with the help of ERP diagram - ERD Diagram allows you to communicate with the logical structure of the database to users

Prime reasons for using the ER Diagram (7)

Attribute

Property or characteristics of entity. It is a single-valued property of either an entity-type or a relationship-type.

Double Ellipses

Represent multi-valued attributes

Step 1) Entity Identification Step 2) Relationship Identification Step 3) Cardinality Identification Step 4) Identify Attributes Step 5) Create the ERD Diagram

Steps to Create an ER Diagram

Ellipses

Symbol represent attributes

Rectangles

This Entity Relationship Diagram symbol represents entity types

- Simple attribute - Composite attribute - Derived attribute - Multivalued attribute

Types of Attributes (4)

A real-world thing either living or non-living that is easily recognizable and nonrecognizable. It is anything in the enterprise that is to be represented in our database. It may be a physical thing or simply a fact about the enterprise or an event that happens in the real world.

WHAT IS ENTITY?

ER Diagram

________ stands for Entity Relationship Diagram, also known as ERD is a diagram that displays the relationship of entity sets stored in a database. In other words, _________ help to explain the logical structure of databases. _______ are created based on three basic concepts: entities, attributes and relationships. ___________ contain different symbols that use rectangles to represent entities, ovals to define attributes and diamond shapes to represent relationships.

ER Model

________ stands for Entity Relationship Model is a high-level conceptual data model diagram. _________ helps to systematically analyze data requirements to produce a well-designed database. The __________ represents real-world entities and the relationships between them. Creating an __________ in DBMS is considered as a best practice before implementing your database.

Relationship

____________ is nothing but an association among two or more entities.

Primary key

attributes are underlined

Lines

It links attributes to entity types and entity types with other relationship types

Diamonds

This symbol represents relationship types

Multivalued attribute

This type of attribute can have more than one values. For example, a student can have more than one mobile number, email address, etc.

Derived attribute

This type of attribute does not include in the physical database. However, their values are derived from other attributes present in the database. For example, age should not be stored directly. Instead, it should be derived from the DOB of that employee.

- Entities - Attributes - Relationships

Three Basic Components of the ER Diagram