Suggest an editImprove this articleRefine the answer for “What are UML diagrams?”. Your changes go to moderation before they’re published.Approval requiredContentWhat you’re changing🇺🇸EN🇺🇦UAPreviewTitle (EN)Short answer (EN)**UML (Unified Modeling Language)** is a universal visual modeling language used to describe, design, and document software systems. It helps present the structure and behavior of a program as diagrams, so project participants understand equally how the system is built and how it works. **Key point:** UML is independent of any specific programming language - it is universal and describes logic, not syntax.Shown above the full answer for quick recall.Answer (EN)Image**UML (Unified Modeling Language)** is a universal visual modeling language used to describe, design, and document software systems. It helps present the structure and behavior of a program *as diagrams*, so project participants can understand equally **how the system is built and how it works**. ### Why UML is needed - makes complex systems understandable without reading the code; - allows errors in architecture and logic to be spotted early; - serves as a common language between analysts, developers, testers, and the client; - helps document a project so it can be maintained and evolved. UML does not depend on a specific programming language - it is universal and describes **logic, not syntax**. ### Main groups of UML diagrams UML is divided into two large types: **structural** (what exists in the system) and **behavioral** (what the system does). #### 1. Structural diagrams - show the *structure* of the system 1. **Class Diagram** One of the most popular. Shows classes, their fields, methods, and the relationships between them (inheritance, associations, compositions). Example: class `User` is linked to `Order`, `User` has `login()`, `logout()`, and `Order` has `calculateTotal()`. 2. **Component Diagram** Displays the logical blocks of a program (modules, libraries) and the dependencies between them. 3. **Deployment Diagram** Shows the physical placement of components on servers, containers, databases, and so on. 4. **Object Diagram** Similar to a class diagram, but shows specific instances of classes and the links between them at a given point in time. 5. **Package Diagram** Used to group classes and modules into logical packages, which helps understand the scale of the system. #### 2. Behavioral diagrams - show the *dynamics* of the system's operation 1. **Use Case Diagram** Displays users (actors) and their interaction with the system. For example: "The user places an order" is one use case. 2. **Sequence Diagram** Shows how objects interact with each other over time: who calls whom, and in what order actions occur. 3. **Activity Diagram** Illustrates the flow of actions or processes. Similar to a flowchart: start → decision → branching → end. 4. **State Machine Diagram** Displays which states an object can be in and how it transitions between them. Example: an order → "created" → "paid" → "delivered". 5. **Communication Diagram** Similar to a sequence diagram, but focuses on the *links between objects* rather than on execution time. ### Tools for creating UML Commonly used: [**Draw.io**](http://Draw.io), **Lucidchart**, **PlantUML**, **StarUML**, **Visual Paradigm**, **Miro**. PlantUML is convenient because it lets you describe diagrams as text instead of drawing them manually. ### Conclusion UML is a visual language that makes the architecture and logic of programs understandable at any stage of development. It helps describe a system **visually, in a structured way, and independently of the code**, which makes it one of the most important tools in the arsenal of analysts, architects, and developers.For the reviewerNote to the moderator (optional)Visible only to the moderator. Helps review go faster.