Guides
13 guides on modeling. Practical writing from the team building Atlas, useful whether or not you buy anything.
Any object that moves through defined states (an order, a subscription, a document) is a state machine hiding in your code. Drawing it makes the illegal transitions obvious before a bug allows one.
The hardest part of UML is not the notation but knowing which diagram to draw. Match the diagram to the question and the rest gets easy.
UML defines fourteen diagram types, but you will use a handful of them constantly and the rest rarely. This guide covers all fourteen and tells you which ones actually earn their place.
An object diagram is a snapshot of specific instances at one moment in time. This guide explains how it complements the class diagram and when a concrete example is worth a thousand abstractions.
SysML is a modeling language built on UML but aimed at whole systems, not just software. This guide compares the two, explains what SysML adds, and helps you decide which you need.
UML has fourteen diagram types split into two families: structural diagrams for what a system is, and behavioral diagrams for what it does. This guide maps them all and helps you pick.
Component diagrams show how a system decomposes into replaceable parts and the interfaces they expose and consume. This guide covers components, ball-and-socket interfaces, ports, and dependencies.
State machine diagrams model how an object moves between states in response to events. This guide covers states, transitions, guards, entry and exit actions, and nested composite states.
Activity diagrams model workflows and business processes with the rigor of UML. This guide covers actions, decisions, concurrency with forks and joins, and swimlanes for responsibility.
A use case diagram maps who uses a system and what they use it to do. This guide covers actors, use cases, boundaries, and the include and extend relationships that trip people up.
Sequence diagrams show how objects collaborate over time by exchanging messages. This guide covers lifelines, message types, activation, and the fragments that model real control flow.
The class diagram is the most useful diagram in UML. This guide covers everything on the box, every line between boxes, and how to draw one that clarifies rather than clutters.
UML is a shared visual language for describing software before you build it. This guide covers what it is really for, all 14 diagram types, and how to use the handful that earn their keep.
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