What are UML diagrams used for?

In the last publication, we got acquainted with the ER diagram, which is an integral part of the database design process. 

In this post, we will delve into the process of designing IT solutions and get acquainted with the diagram of the UML - Unified Modeling Language (Unified Modeling Language).

UML is a standard used to visualize and model the architecture of a project. It is a set of graphic symbols and notations that facilitate the perception of a complex project for all team members.

There are different types of UML diagrams. Let's talk about them.

Varieties of UML

Class diagram. Imagine the database entity as a separate class with its own attributes. In addition to attributes, a class can have its own methods. And classes can also depend on each other. 

Let's look at a concrete example. Suppose we have a class "Product", which has the attributes "name", "price", "category". This class can have methods: "create a product", "delete a product", "edit a product", "search for a product" and others. In addition, this class has a relationship with another class — "Product category". 

Agree, it's a bit difficult to perceive such a text, so we came up with a class diagram in which this text is graphically displayed.

Use case diagram.  In any business process there is an actor, someone who performs an action. We also have, in fact, the action itself. This diagram graphically reflects the actors and what actions they perform.

Sequence diagram. This is a detailed representation of the precedent diagram. The sequence diagram contains the objects that participate in the process, as well as the messages that the objects exchange. There are also results of this exchange. 

Process example: 

1. The "User" has clicked the "Checkout" button;

2. The "Server" created an object of the "Payment" entity in the DB;

3. The "Server" sent a request to the "Bank" to receive a payment link;

4. The "Bank" returned the payment link to the "Server";

5. The "Server" sent the payment link to the user;

6. The "User" made the payment;

7. The "Bank" has returned information about the successful transaction to the server;

8. The "User" is redirected to the previous page.

A diagram of states. Displays the various states in which an object or system can be located, and transitions between these states.

Activity diagram. These are processes presented in the form of a logical flowchart. On this flowchart there is a start point of the process, there is a completion point. The flow of actions is located between these two points. 


1. Woke up in the morning;

2. Washed up;

3. If you did not oversleep, then point 4, and if you overslept, point 5;

4. I've been doing sports;

5. Got dressed;

6. Went to work.

Component diagram. It is a map of all system components and their connections. This diagram allows you to model the overall picture of an IT solution.

Deployment diagram. Shows the physical placement of system components on the hardware.


UML diagrams are a very useful tool for designing IT solutions. It allows you to sort out an IT product with a complex architecture. As a rule, UML diagrams are used in medium or large projects.



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