UML diagrams: all 14 types explained

Read in order

Every UML diagram, explained

2. 02UML symbolsThe symbols UML actually uses, across every diagram type: boxes, ellipses, diamonds, bars and 3D nodes, plus the six relationship lines and the arrowheads that tell them apart.Notation reference8 min read
3. 03Choosing a diagramA decision guide to the fourteen UML diagram types: what each answers, which four carry most real work, and which are safe to skip until you meet one.Foundations9 min read
4. 04Class diagramsHow to read and draw a UML class diagram: the three compartments, visibility markers, multiplicity, and the difference between association, aggregation, composition, generalization and realization.Structure diagrams11 min read
5. 05Class diagram examplesWorked UML class diagram examples: a library with an abstract base class and two subtypes, and a shopping basket with composition, an interface and two realizations.Structure diagrams6 min read
6. 06How to draw a class diagramA step-by-step method for drawing a UML class diagram: which nouns become classes, how to choose a relationship kind, when multiplicities get decided, and when to stop adding detail.Structure diagrams7 min read
7. 07Class diagram symbolsA reference for UML class diagram notation: the six relationship kinds and their arrowheads, the three visibility markers, multiplicity syntax, and what a stereotype in guillemets means.Notation reference11 min read
8. 08Sequence diagramsHow to read and draw a UML sequence diagram: lifelines, activation bars, synchronous and asynchronous messages, replies, and the combined fragments (alt, opt, loop, par) that handle branching.Behaviour diagrams15 min read
9. 09Sequence diagram examplesWorked UML sequence diagram examples: a login with an alt fragment, a payment retry with a loop and a self-call, and an asynchronous event publication with no replies at all.Behaviour diagrams6 min read
10. 10How to draw a sequence diagramA step-by-step method for drawing a UML sequence diagram: picking one scenario, choosing participants, ordering messages left to right, adding fragments, and knowing when to split the diagram.Behaviour diagrams7 min read
11. 11Use case diagramsHow to read and draw a UML use case diagram: actors, the system boundary, associations, and the include and extend relationships that people most often get backwards.Behaviour diagrams13 min read
12. 12Use case examplesWorked UML use case diagrams for a library and an online store, with include, extend and a secondary actor, followed by the same notation used badly and why it fails.Behaviour diagrams8 min read
13. 13Activity diagramsHow to read and draw a UML activity diagram: actions, decisions and merges, forks and joins, guards, swimlanes, and the difference between a branch and true parallelism.Behaviour diagrams9 min read
14. 14Activity examplesWorked UML activity diagrams: parallel work behind a fork and join, a three-way branch with exhaustive guards, and the difference between a flow final and an activity final in one picture.Behaviour diagrams8 min read
15. 15State machine diagramsHow to read and draw a UML state machine diagram: states, transitions with trigger, guard and effect, entry and exit actions, composite states, and history pseudostates.Behaviour diagrams9 min read
16. 16State machine examplesWorked UML state machine diagrams: an order lifecycle ending two different ways, a review workflow with a transition back to draft, and triggers versus guards on the way out of a state.Behaviour diagrams8 min read
17. 17Component diagramsHow to read and draw a UML component diagram: components, provided and required interfaces, ball-and-socket notation, ports, and how it differs from a class diagram.Structure diagrams13 min read
18. 18Component examplesFive worked UML component diagram examples - a shared catalogue, ports and adapters, a legacy swap, a plugin architecture and a dependency cycle - with what each one is for.Structure diagrams9 min read
19. 19Drawing a component diagramA step-by-step walkthrough: choose the parts, draw the boxes, name what each provides, add what each requires, then run the four checks that tell you the diagram is finished.Modelling practice8 min read
20. 20Component symbolsA reference for every symbol on a UML component diagram: the component box, provided and required interfaces, ball and socket, assembly and delegation connectors, ports and stereotypes.Notation reference7 min read
21. 21Deployment diagramsHow to read and draw a UML deployment diagram: nodes, devices and execution environments, artifacts, communication paths, and the deploy relationship.Structure diagrams7 min read
22. 22Deployment examplesWorked UML deployment diagrams: a classic three-tier stack, a Kubernetes cluster with container images as artifacts, and a horizontally scaled pool behind a load balancer.Structure diagrams8 min read
23. 23Object diagramsHow to read and draw a UML object diagram: instance specifications, underlined names, slots with concrete values, links, and how to use one to sanity-check a class diagram.Structure diagrams6 min read
24. 24Package diagramsHow to read and draw a UML package diagram: packages, import and access dependencies, merge, nesting, and using the dependency direction to enforce a layered architecture.Structure diagrams6 min read
25. 25Composite structure diagramsHow to read and draw a UML composite structure diagram: parts, ports, connectors, delegation, and the difference between this and a class or component diagram.Structure diagrams6 min read
26. 26Communication diagramsHow to read and draw a UML communication diagram: objects, links, numbered messages, nested decimal sequencing, and when to prefer it over a sequence diagram.Behaviour diagrams6 min read
27. 27Sequence vs communicationOne interaction drawn as both a sequence diagram and a communication diagram, with what each makes obvious, what each hides, and how to pick between them.Behaviour diagrams7 min read
28. 28Timing diagramsHow to read and draw a UML timing diagram: lifelines as value axes, state-change waveforms, duration and time constraints, and when elapsed time matters enough to need one.Behaviour diagrams6 min read
29. 29Interaction overview diagramsHow to read and draw a UML interaction overview diagram: interaction occurrences, inline interactions, control flow between them, and how it keeps large sequence diagrams manageable.Behaviour diagrams5 min read
30. 30Profile diagramsHow to read and draw a UML profile diagram: stereotypes, metaclasses, the extension relationship, tagged values, and when extending the language is better than working around it.Structure diagrams6 min read
31. 31UML with AIWhat an AI UML generator is actually good at, the four errors it repeats, how to prompt for a diagram worth keeping, and the two-minute review that catches the rest.Modelling practice9 min read
32. 32E-commerce exampleA complete worked example of an e-commerce architecture: the domain model, the component view with its service contracts, and the deployment topology, with what each one is for.Modelling practice9 min read
33. 33Banking exampleA worked banking system example in UML: the double-entry domain model where a balance is derived rather than stored, and the state machine a transfer moves through.Modelling practice8 min read
34. 34Microservices exampleA worked microservices architecture example: where to put synchronous contracts, where to publish events instead, and how to spot a distributed monolith on paper.Modelling practice8 min read
35. 35AWS exampleA worked AWS architecture example in UML: the deployment topology with real protocols and ports, and the component view where the vendor names turn back into contracts.Modelling practice8 min read

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