ER Model vs. UML diagram

    

ER model

What is the ER model?

The full-form of ER model is Entity-Relationship model. It is a model which is used to

describe the relationship between data-elements in a database  system. This ER model is

generally portrayed using an ER diagram. It is widely used in various organizations as it is

really simple and easy to understand, with just a glance a person can understand each and

every aspect of the backend architecture.

Components of ER model

Entity:

1. An entity can be anything ranging from a person, place or object. It is generally represented using a rectangle. For example, faculty, student, department, college all can be termed as entities.Weak Entity: An entity which depends on another entity is called a weak entity. It

            represented with double-rectangle and does not have a key attribute of its own

Attribute:

2. The attribute is used to describe the property of an attribute. It is described using an oval.

            a. Key Attribute: It is used to describe the most important attribute of an entity
                i.e its primary key. It is described using oval and text inside it is underlined.
            b. Composite Attribute: It is the attribute of an attribute i.e the nested attribute. 
                It is usually a chain of oval connected to each other with a line.
            c. Multi-valued Attribute: It is the kind of attribute which can have multiple values. 
                 It is generally represented using a double oval.
            d. Derived attribute: The attribute which can be derived from other attribute can be

                called as derived attribute. It is represented using dashed oval.

Relationship:

3. A relationship is used to describe the relation between different entities. It is generally represented using rhombus or diamond.

1. One-to-one relationship:

When only one instance of an entity is connected to its relationship,

then it is called a one-to-one relationship.

2. One-to-many relationship:

   When there is only one entity present on the left and instance of more than

                        one entity on the right then it is called a one-to-many relationship.

3. Many-to-one relationship:

   When an instance of more than one entity is on the left and only one entity is

                        present on the right then it can be called a many-to-one relationship.

4. Many-to-many relationship:

When the instance of more than one entity binds with instance of more than one

                        instance entity then the relationship can be termed as many-to-many

                        relationship.

How to draw an ER diagram

1. Have a defined goal and purpose of drawing the ER diagram. It may be drawn for

           business needs or for database creation.

1. Know the constraints and limitations of the system you are trying to build.

2. Draw major entities of the system.

3. Investigate the several properties involved in the entities.

4. Consider the relationship between several entities.

5. Use database normalization to restructure the data.

Limitations of ER diagram

1. Can only be used for relational data.

2. No industry standard as everyone has their own idea of developing an ER model.

3. Some data may be lost in abstraction of concepts.

UML Diagram

UML is a way of visualizing software programs using a collection of diagrams. It is called as
Unified Modeling Language.

What is UML?

UML is known as Unified Modeling Language. UML 2.0 helps to extend the original UML specification

to cover a wider portion of software development including agile practices.

Types of UML Diagrams

The current UML has almost 13 different types of diagrams:communication, composite structure, timing, 

deployment , class, activity, object, use case, sequence, package, state, component and  interaction

overview.

These all diagrams are organized into two main distinct groups,

1. Structural diagrams and

2. Behavioral or interaction diagrams

Structural UML diagrams:

• Class diagram
• Package diagram
• Object diagram
• Component diagram
• Composite structure diagram
• Deployment diagram

Behavioral UML diagrams:

• Activity diagram
• Sequence diagram
• Use case diagram
• State diagram
• Communication diagram
• Interaction overview diagram
• Timing diagram

 

Structural diagram:

UML Structural diagrams represent the elements of a system that are independent of time and

that conduct the concepts of a system and how they relate to each other. In these diagrams the elements

resemble a natural language, and the relationships  connecting them are structural or semantic

relationship.For example, a structural diagram of a vehicle reservation system might contain elements

such as Car, Reservation, Driver’s License and Credit Card, and connectors linking these elements.

Experienced modelers are  also shows relationships to the Behavioral elements on these diagrams.

Behavioral diagram:

UML Behavioral diagrams specify, construct, visualize, specify, construct and document the
dynamic aspects of a system.

Class Diagram:

Class diagram is the main building block of any object-oriented solution.

It shows the classes in a system, attributes, and operations of each class

and the relationship between every class.In most of the modeling tools, basically the

class has three parts. Name is at the top, attributes in the middle and operations or

methods at the bottom of it. In the large system with many related classes, these

classes are grouped together to create class diagrams. Different relationships

between these classes are shown by different types of arrows.

 

Component Diagram:

A component diagram which displays the structural relationship of components of a software
system. These are mostly Commonly  used when working with complex systems with many
components. These  Components communicate with each other using interfaces. The interfaces are linked using connectors.

Deployment Diagram:A deployment diagram is a diagram that which shows the hardware of your system and the
software which is present in that hardware. Deployment diagrams are more useful when your
software solution is deployed across multiple machines with each of them  having a unique
configuration.

Object Diagram

It sometimes these are referred to as Instance diagrams, which  are very similar to class
diagramsLike every class diagram, they also show the relationship between the objects but they use
real-world examples.They show what the  system will look like at a given time. Because
there is  availability of data  in the objects, they are used to explain complex relationships
between objects.

Composite Structure Diagram
Composite structure plates it used to show the internal structure of a class, And some of the
common compound Structure Diagram. 

Profile Diagram PD is a new illustration type which is introduced in UML 2. This illustration type is veritably
infrequently used in any specification. 

Package Diagram
The Package Diagram shows dependences between different packages in a system.

Exertion Diagram The exertion plates are represent workflows in a graphical way. It can be used to describe the
business workflow of any element in a system. Some times exertion illustration are used as a
violation to State machine plates.

 Use Case Diagram 

The UCD is the most important illustration type in the Behavioral UML types, It uses case
illustration it principally give an graphic overview of the actors involved in a system, some
of this different functions demanded by those actors and how these different functions
interact with UCD.

State Machine Diagram 

The State Machine Diagram is analogous to exertion plates, although sundries
beach operation change a bit. They're occasionally known as state map illustration. These are
really veritably useful illustration to describe the geste  of objects which acts else according
to the state which they're in the state. 

Timing Diagram 

This Timing plates is veritably analogous to sequence plates. It represent the geste of objects in a given time frame. If it's an only one object also the illustration is straightforward. But, if there's further than one object involved, a Timing illustration is used to show relations between objects during that time frame. 

 Sequence Diagram 

In UML Sequence Diagram show how objects interact with each other and the order those 
relations do. It's important to note that it show the relations for a particular setivations. The
processes of sequence illustration represented vertically and relations are shown as arrows.

Differences between ER Model and UML Diagram

1. ER Model stands for Entity-Relationship Model whereas UML stands for Unified Modelling Language
2. ER Model consists of Entities, Relationships and their interactions whereas UML consists of work processes and use cases.
3. ER Model is generally used by developers to understand the flow of program whereas UML diagram is generally used by Business owners and stakeholders to easily understand the software architecture
4. ER Model is a static modelling where there are no states of it, whereas UML diagram implements dynamic modelling which depicts the activities and various states/cases involved in it.
5. ER Model does not have any types but UML diagram consists of Structural and Behavioral type diagrams.
6. ER Model is itself a representation of the architecture whereas UML diagram has various diagrams such as activity diagram, sequence diagram, use-case diagram etc.