The Unified Modeling Language

Activity diagrams and sequence diagrams were enhanced. Activities were redesigned to use a Petri-like semantics. Edges can now be contained in partitions. Partitions can be hierarchical and multidimensional. Explicitly modeled object flows are new.

Classes have been extended with internal structures and ports (composite structures). Information flows were added. A collaboration now is a kind of classifier, and can have any kind of behavioral descriptions associated. Interactions are now contained within classifiers and not only within collaborations. It is now possible for use cases to be owned by classifiers in general and not just packages.

New notation for concurrency and branching using combined fragments. Notation and/or semantics were updated for components, realization, deployments of artifacts. Components can no longer be directly deployed to nodes. Artifacts should be deployed instead. Implementation has been replaced by «manifest». Artifacts can now manifest any packageable element (not just components, as before). It is now possible to deploy to nodes with an internal structure.

New metaclasses were added: connector, collaboration use, connector end, device, deployment specification, execution environment, accept event action, send object action, structural feature action, value pin, activity final, central buffer node, data stores, flow final, interruptible regions, loop nodes, parameter, port, behavior, behaviored classifier, duration, interval, time constraint, combined fragment, creation event, destruction event, execution event, interaction fragment, interaction use, receive signal event, send signal event, extension, etc.

Many stereotypes were eliminated from the Standard UML Profile, e.g. «destroy», «facade», «friend», «profile», «requirement», «table», «thread».

Integration between structural and behavioral models was improved with better support for executable models.

There are no longer two separate infrastructure and superstructure documents, the UML 2.5 specification is a single document. Package merge is no longer used within the specification.

Four UML compliance levels (L0, L1, L2, and L3) are eliminated, as they were not useful in practice. UML 2.5 tools will have to support complete UML specification. Information flows, models, and templates are no longer auxiliary UML constructs. At the same time, use cases, deployments, and the information flows became "supplementary concepts" in UML 2.5.

UML 2.5 has a number of fixes, clarifications, and explanations added. They updated description for multiplicity and multiplicity element, clarified definitions of aggregation and composition, and finally fixed wrong «instantiate» dependency example for Car Factory. New notation for inherited members with a caret '^' symbol was introduced. UML 2.5 clarified feature redefinition and overloading. They also moved and rephrased definition of qualifiers.

Default for generalization sets was changed from {incomplete, disjoint} to {incomplete, overlapping}.

There are few clarifications and fixes for stereotypes, state machines, and activities. Protocol state machines are now denoted using «protocol» instead of {protocol}. Use cases are no longer required to express some needs of actors and to be initiated by an actor.