SysML tool

SysML diagrams online, connected to one model.

Draw SysML block definition, internal block, parametric, activity, sequence, state machine, use case, requirement and package diagrams in your browser. Every box, port and line is an item in the project's model, so the diagrams stay consistent with your requirements, interfaces, budgets and tests.

Start free Read the SysML reference

SysML internal block diagram of the CubeSat electrical power system: solar arrays, power distribution unit and battery pack connected by power interfaces

The nine SysML diagram types

Pick the diagram by the question you need to answer. Each one opens on a root item and draws what the model says about it.

Block definition diagram

The system breakdown: blocks with values, constraints, operations and ports, and composition, aggregation and associations.

Internal block diagram

Parts, ports, connectors and item flows inside a block. Connectors feed the interface register and the ICD.

Parametric diagram

Constraint blocks bound to block values and solved with units, for power, mass and link budgets.

Activity diagram

An action flow in activity notation, with pins and swimlanes. Run it in the simulator.

Sequence diagram

Lifelines and the messages they exchange, drawn from the same action flow.

State machine diagram

Operational modes and fault behavior: states, composite and parallel states, regions and transitions.

Use case diagram

Who uses the system and for what: use cases, actors, include and extend, and the system boundary.

Requirement diagram

How requirements derive from each other, and what satisfies and verifies each one.

Package diagram

Nested packages and their dependencies, to organize a large model.

UML class diagrams are also available, with import from Java source.

Diagrams that are views, not drawings

Adding a block creates an item in the model and the relationship that places it. Removing it from a diagram leaves the item in the model.
The same block can appear on several diagrams at once. Edit it in one and the others follow.
The activity diagram, the action diagram and the FFBD edit one flow, so behavior is never drawn twice.
Parametric results, interface capacity checks and the RVTM read the same values as the diagrams.

Interface register listing each interface with its endpoints, status, owner, conveyed items, requirements and a capacity check that flags one link as over capacity

Bring in an existing SysML model

Import XMI 2.x with UML 2.5 and the SysML 1.x profile (1.3 to 1.7).
Works with exports from Cameo Systems Modeler or MagicDraw (including .mdzip project files), Enterprise Architect, IBM Rhapsody and Papyrus.
Requirements, blocks, parts, ports, activities with their flow, state machines, test cases and satisfy, verify and derive relationships come along.
Re-import a later export and match existing items by number or name. See Import and export.

What Holarch is, precisely

Holarch is a model-based systems engineering workbench whose model is built on the Lifecycle Modeling Language (LML). SysML diagrams are views of that model: a block is an Asset, a connector is a Conduit and a constraint block is an Equation. See LML.
The diagrams follow SysML 1.x notation. SysML v2 files use a different format and are not imported.
XMI is an import format. To exchange requirements with other tools, Holarch writes ReqIF, Word and Excel.

Free for classes

Students and instructors use Holarch free, with nothing to install. See For classes.
The Free plan covers every modeling feature for personal, educational and evaluation use. See Pricing.

More than diagrams

Requirements documents, verification, risk and trade studies work on the same model. See Holarch as an MBSE tool.
New to model-based work? Read what MBSE is.