What are the differences between UML 1.x and UML 2.x and how do they affect your tool selection?

1 UML 1.x overview

UML 1.x was the first series of UML versions, released between 1997 and 2005. It consisted of 13 diagram types, organized into four categories: structure, behavior, interaction, and use case. UML 1.x aimed to provide a common notation and semantics for modeling various aspects of software systems, such as classes, objects, components, collaborations, activities, states, and scenarios. UML 1.x was widely adopted by software developers, architects, and analysts, and supported by many tools and platforms.

2 UML 2.x overview

UML 2.x was the second series of UML versions, released between 2003 and 2017. It introduced significant changes and enhancements to UML 1.x, such as adding new diagram types, expanding existing ones, refining the syntax and semantics, and improving the alignment with other standards and languages. UML 2.x consisted of 14 diagram types, organized into two categories: structure and behavior. UML 2.x aimed to address the limitations and challenges of UML 1.x, such as modeling complex and dynamic systems, supporting model-driven development, and enabling more precise and rigorous specifications.

3 Diagram differences

One of the most noticeable differences between UML 1.x and UML 2.x is the number and type of diagrams. UML 2.x added two new diagram types: composite structure and timing. Composite structure diagrams show the internal structure and interactions of a component or a class, while timing diagrams show the temporal behavior and constraints of objects and events. UML 2.x also modified some of the existing diagram types, such as replacing collaboration diagrams with communication diagrams, adding interaction overview diagrams as a variant of activity diagrams, and introducing state machine diagrams as a generalization of statechart diagrams.

4 Syntax differences

Another difference between UML 1.x and UML 2.x is the syntax and notation of the diagrams. UML 2.x introduced new symbols, icons, and keywords to represent new or refined concepts, such as ports, parts, connectors, lifelines, gates, regions, forks, joins, signals, events, triggers, guards, effects, actions, pins, nodes, artifacts, and stereotypes. UML 2.x also changed some of the existing symbols and rules, such as using dashed arrows for dependencies, adding labels for association ends, using rectangles for classes and objects, and using curly brackets for constraints.

5 Semantic differences

A third difference between UML 1.x and UML 2.x is the semantics and meaning of the diagrams. UML 2.x enhanced the expressiveness and precision of UML 1.x, by defining more rigorous and consistent rules and definitions for the elements and relationships of the diagrams. UML 2.x also aligned the semantics of UML with other standards and languages, such as the Meta-Object Facility (MOF), the Object Constraint Language (OCL), the XML Metadata Interchange (XMI), and the Action Semantics for UML (ASU). UML 2.x also supported the notion of profiles, which are extensions of UML for specific domains or purposes.

6 Tool differences

A final difference between UML 1.x and UML 2.x is the availability and compatibility of tools for creating and modifying UML diagrams. Since UML 2.x is the latest and most comprehensive version of UML, it is recommended to use tools that support UML 2.x features and standards. However, not all tools are fully compliant with UML 2.x, and some may only support a subset of diagrams or elements. Moreover, some tools may still use UML 1.x notation or semantics, or allow importing or exporting UML 1.x models. Therefore, it is important to check the specifications and capabilities of the tools before choosing them for your UML projects.

7 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?