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Clear out junk files and repair common Windows errorsFree Scan →Scan for outdated or missing drivers - takes under a minuteDriver Scan →The Unified Modeling Language (UML) is a standardized visual language for representing and documenting software and systems. The Object Management Group (OMG), which publishes the specification, describes it as a standard for visualizing, specifying, and documenting software and systems. In practice, UML gives engineers a shared set of diagram types and modeling concepts so a design can be drawn, discussed, and recorded consistently. It is a notation and a set of concepts, not a programming language.
What UML is used for
ISO describes the objective of UML as providing tools for the analysis, design, and implementation of software-based systems, and for modeling business and similar processes. The sentence below is from the abstract of ISO/IEC 19505-2:2012, published by ISO. It is an official organizational statement, not a quotation from a named person:
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“The objective of UML is to provide system architects, software engineers, and software developers with tools for analysis, design, and implementation of software-based systems as well as for modeling business and similar processes.”
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Teams typically reach for UML at three points: when analyzing a problem (what the system must do and who interacts with it), when designing it (how its parts are structured and how they interact over time), and when documenting what was built. The same notation can also describe business processes, which is why ISO’s wording extends beyond software.
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Which UML version and standard to cite
Two separate standards records are relevant, and they should not be conflated:
- OMG UML 2.5.1. This is the formal version listed on OMG’s specification page, with adoption dated December 2017. The page provides the normative specification and machine-readable metamodel artifacts. When you cite UML in a document, give the version and date from this record.
- ISO/IEC 19505-2:2012. This is a related ISO standard for the UML Superstructure. ISO reports that this edition was last reviewed and confirmed in 2025, so it remains current in ISO’s record.
The OMG adoption date and the ISO edition date belong to different records and should be cited separately.
How the specification is organized
UML 2.5.1 groups its modeling concepts into structural, behavioral, and supplementary parts. The table below summarizes the clause layout as described in the specification document.
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| Clauses or annexes | Primary focus | What it covers |
|---|---|---|
| Clauses 7–12 | Structure | The static parts of a model and how they relate |
| Clauses 13–17 | Behavior | How elements act, interact, and change over time |
| Clauses 18–20 | Supplementary concepts | Use cases, deployments, and information flows |
| Annexes | Reference material | UML diagrams, diagram interchange, keywords, alternative tabular notations, and XMI serialization |
Structural and behavioral modeling
The structure and behavior split is the most useful way to understand what UML can express.
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Structural models
Structure diagrams show what elements exist in a system and how they relate. A class diagram, for example, shows types, their attributes and operations, and the associations between them. Structural models answer the question “what is the system made of?”
Behavioral models
Behavior diagrams show how things happen. A sequence diagram shows the order of messages exchanged between objects, a state machine diagram shows how an element moves between states, and an activity diagram shows the flow of actions. Behavioral models answer the question “how does the system act?”
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Choosing a diagram for the question you need to answer
The mapping below is editorial guidance rather than a formal UML requirement. The specification defines the diagram types; it does not prescribe audiences or detail levels.
| Question you need answered | Aspect modeled | Typical audience | Usual level of detail |
|---|---|---|---|
| What parts exist and how do they relate? | Structure | Developers and architects | Detailed, with types and relationships |
| How does an interaction unfold step by step? | Behavior | Developers and testers | Detailed, with message order |
| What must the system do, and who uses it? | Supplementary (use cases) | Stakeholders and analysts | High level |
| Where does the software run? | Supplementary (deployment) | Operations and architects | Infrastructure level |
What UML is not
- It is not a programming language. It defines modeling concepts and notations; the specification does not define a runtime or executable code.
- It is not a development process. UML specifies what can be drawn and what the drawings mean, not how a team should schedule or run its work.
Where to learn UML and find authoritative references
Start with the OMG specification for normative definitions. OMG’s overview page points to learning resources and UML certification. A UML modeling textbook or reference book is a practical companion for learning the notation, but when a book and the specification differ, the specification is the standards source. OMG’s overview does not name specific training providers, so check any course against OMG’s current listings before relying on it.
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