OpenSysML

README

Open Source SysML v2 Implementation

OpenSysML is a SysML v2 and KerML 1.1 implementation in Go. It provides a language server, an interactive REPL, an execution runtime, an embeddable Go API, and Python, Node/TypeScript, Java and Rust client libraries, covering the lifecycle from authoring through execution with the integrated tooling systems engineers expect from a modern language ecosystem.

The basis for these claims, and their limits, are documented in spec compliance and the pilot differential: every diagnostic is compared against the pinned OMG pilot implementation over that implementation's own corpora, and no conformance certification is claimed.

Quick start

Introductory material: the guide

Complete searchable documentation: https://opensysml.org/ — the same pages as docs/, rendered from main.

Install

Download pre-built binaries:

# Linux x64 (use opensysml-linux-arm64.tar.gz on arm64)
wget https://github.com/Open-MBEE/OpenSysML/releases/latest/download/opensysml-linux-amd64.tar.gz
tar xzf opensysml-linux-amd64.tar.gz && sudo mv sysml sysml-lsp /usr/local/bin/

# macOS (Intel or Apple Silicon) — see the note below
brew install Open-MBEE/tap/opensysml

With a Go toolchain (no download, never quarantined):

go install github.com/Open-MBEE/OpenSysML/cmd/sysml@latest
go install github.com/Open-MBEE/OpenSysML/cmd/sysml-lsp@latest

Or build from source:

make build
./bin/sysml

macOS — use Homebrew. The released binaries are not Developer ID signed or notarized, so a tarball downloaded in a browser carries com.apple.quarantine and Gatekeeper shows "cannot be opened because the developer cannot be verified". Homebrew downloads with curl, which never sets that attribute, so brew install avoids the prompt entirely. When the tarball is downloaded directly (curl -fL ... opensysml-darwin-arm64.tar.gz, followed by xattr -d com.apple.quarantine), see the guide. Signing and notarization are the intended long-term resolution — docs/project/macos-distribution.md.

Install by the fully-qualified name. Homebrew 6 requires third-party taps to be trusted before their Ruby is loaded, and brew install Open-MBEE/tap/opensysml trusts just that formula. brew tap Open-MBEE/tap && brew install opensysml needs brew trust --formula Open-MBEE/tap/opensysml in between.

Examples

Interactive modeling:

$ sysml
sysml> part def Wheel { attribute diameter = 16.0; }
✓ part def Wheel

sysml> %instantiate Wheel
✓ Created instance of Wheel
  ID: 1
  Use %features Wheel to inspect

sysml> %features Wheel
Instance: Wheel (ID: 1)
Features:
  diameter = 16.0

Behavioral execution:

sysml> calc add { in x; in y; x + y }
✓ calc add

sysml> %calc add 10 20
✓ add(10, 20)
  = 30

sysml> constraint ValidSpeed { 65 <= 120 }
✓ constraint ValidSpeed

sysml> %constraint ValidSpeed
✓ Constraint ValidSpeed passed

Action & state debugging:

sysml> action MyWorkflow { attribute result = 0; first start; then action compute { assign result := 42; } then done; }
✓ action MyWorkflow

sysml> %action MyWorkflow
✓ Started action executor for "MyWorkflow"
  State: Running
  Tokens: 1

Use %step to advance, %tokens to inspect, %continue to run to completion

sysml> %break compute
✓ Breakpoint set at node "compute"
  %continue runs until a token reaches it

sysml> %continue
⏸ Paused at breakpoint "compute"
  State: Suspended
  Tokens: 1

Use %tokens to inspect, %step or %continue to resume

sysml> %tokens
Active tokens (1):
  Token 1 @ compute
  Values:
    result = 0

sysml> %continue
✓ Action completed
  Final state: Completed
  Results:
    result = 42

sysml> state TrafficLight { entry; then red; state red; state green; transition first red then green; }
✓ state TrafficLight

sysml> %state TrafficLight
✓ Started state machine executor for "TrafficLight"
  Current state: red
  Time: 0.0
  Events: 1

Use %events to see queue, %current for state, %advance <time> to step

sysml> %advance 30
✓ Advanced to 30.0 (1 event(s) processed)
  Current state: green
  Last event at: 0.0
  Remaining events: 0

Further demonstrations are available in examples/repl-behavioral-demo.sysml.

---

Overview

The project provides the tooling familiar from the Python, Rust and Go ecosystems, applied to SysML v2:

• Language Server — A standard LSP server (sysml-lsp) with live diagnostics, semantic hover, go-to-definition, find references, completion, workspace-wide symbol search, formatting, rename, semantic tokens and quick fixes. A VS Code extension with TextMate grammars for .sysml and .kerml ships in editors/vscode, and any editor with a generic LSP client can drive the server directly — guide chapter 8 walks through both. Not yet: the extension is built from source rather than published to a marketplace, and the server answers no semantic token delta requests or signature help.
• Interactive REPL — An exploratory modeling environment: define models incrementally, evaluate expressions interactively, instantiate parts, run calculations and inspect runtime state, comparable to IPython or Jupyter for systems engineering.
• Constraint Solving (experimental) — In addition to evaluating what holds of an object, an external SMT solver determines whether a constraint, requirement or satisfaction assertion can hold, which conditions conflict when it cannot, which values would satisfy it, which variants a model permits, and what optimizes an analysis def's objectives. The solver is optional and discovered at runtime. The REPL command reference documents each command, and installing a solver describes how to obtain one.
• Execution Runtime — More than a validator: instantiate parts, evaluate constraints against concrete values and execute calc and analysis cases. Action and state executor infrastructure is complete (activity fork/join parallelism, decision guards, hierarchical/orthogonal states, choice/junction pseudostates, TimeEvent/ChangeEvent/AcceptEvent, sourceless transitions). See spec compliance for measured behavioral coverage.
• Embeddable Go API — client/opensysml is the public Go surface: parse, look up symbols, evaluate expressions and instantiate parts from Go code, answered in process by the engine the calling binary already links (no port, no child process and no serialization round trip), or over the Connect protocol against an externally hosted service. See client/opensysml/README.md.
• Python Client Library — gRPC-based Python bindings for programmatic access: parse models, resolve symbols, evaluate expressions, instantiate parts, execute actions/state machines. Includes IPython display hooks for Jupyter notebooks and pandas DataFrame integration. Constraint, requirement, satisfaction and calc verdicts are available as RPCs (verify_constraint, verify_requirement, verify_satisfaction, calc).
• Node/TypeScript Client Library — @opensysml/client for Node and the browser, over the Connect protocol with protobuf bodies: parse, evaluate, look up symbols and instantiate, with values as discriminated unions. No native addon and nothing downloaded at install time (clients/node/README.md).
• Java Client Library — io.github.open-mbee:opensysml-client for a JVM host application it does not own, on the JDK's own java.net.http.HttpClient, so no gRPC, Netty or tcnative reaches the host (clients/java/README.md).
• Rust Client Library — A blocking client for the local sysml-grpc service, with no asynchronous runtime in its default dependency tree, available from the Rust crate documentation.

Guidance on selecting a client, the coverage of the four newer clients, and the functionality they intentionally defer to a future version is provided in docs/reference/clients.md.

• Modern Toolchain — Incremental compilation, a bundled standard library and persistent semantic caches. A model is a set of files, named on the command line or opened by the editor.

Goals

• Performance: sub-millisecond parsing, a single static binary, and no JVM or Eclipse runtime
• Completeness: SysML v2 textual notation support (96 of 96 standard library files parse cleanly: 94 vendored OMG files and 2 OpenSysML extensions)
• Executable models: instantiate, evaluate and simulate, turning specifications into running systems
• Practical ergonomics: multi-file workspaces, incremental analysis and detailed diagnostics

Status

The project is under active development, with the core infrastructure operational:

Component	Status
Lexer/Parser (structural + behavioral grammar)	✅ Operational (96/96 stdlib clean - see conformance gate)
Symbol resolution & type system	✅ Complete
Semantic layer (operators, builtins, validation)	✅ Complete
Feature chain resolution (member access)	✅ Complete
Validation passes (typing conformance, redefinition)	✅ Complete
Native document-query planning	🚧 Query definitions, typed immutable plans, named composition, cycle checks and diagnostics complete; execution and Markdown rendering are not yet implemented
Expression evaluator & instance model (runtime Tiers 1-3)	✅ Complete
Runtime operators (equality, logical, negation)	✅ Complete
Workspace/reindex/file watching	✅ Complete
Behavioral parser (unified grammar with graceful fallback)	✅ Complete (146 golden ASTs, 261 negative tests)
Calc invocation, constraint & requirement evaluation	✅ Complete (conformance gate: 106 calc/constraint/requirement/satisfy cases passing)
Action execution engine (Tier 5)	✅ Complete (70 conformance cases passing)
State machine runtime (Tier 5)	✅ Complete (84 conformance cases: transitions, accept events, sourceless)
REPL debugging commands	✅ Complete — %constraint, %requirement, %satisfy and %calc also answer from the command line (-constraint, -requirement, -satisfy, -calc) and over gRPC, on one evaluation
Model save to notation (%save model.sysml, sysml -convert sysml)	✅ Complete — writes the source through the formatter, so comments and spacing survive
SysML ↔ RDF Turtle conversion (%save model.ttl, sysml -convert ttl)	🧪 Experimental — packages, definitions, usages, ports, connections, values, documentation, and the nodes an action or state body states (260 of 334 examples/ models convert; what is not mapped is refused with the construct named), but the vocabulary may change without a compatibility path. Every run says so; see the RDF mapping's status and worked example
View rendering (%render <view>, sysml -render)	✅ Complete for the kinds produced — containment tree, interconnection diagram, state machine, action flow, sequence diagram and table, as indented text or in the kind's machine-readable form (Mermaid, Markdown). State and action renderings read the graph the runtime executes; the notation itself is tool-defined (SysML v2 §10.2)
Constraint solving (%check, %explain, %solve, %configure, %optimize)	🧪 Experimental — an external SMT-LIB 2 solver decides whether conditions can be satisfied, explains an unsat with a minimal unsat core, synthesises satisfying values, enumerates the variant selections a model permits and optimizes an analysis def's objectives (optimization needs z3, which implements it). The solver is optional and discovered on PATH or through OPENSYSML_SMT; a build with none reports that rather than a verdict — see installing a solver
Source-preserving model edits (ApplyEdits, model.edit())	✅ Complete for four operations — set a feature's value, rename a declaration, add a member, and delete a declaration — rewriting the bytes of the model's own source so every untouched byte is identical. A rename rewrites the references to the renamed element too, and a non-cascade deletion of a referenced element is refused rather than approximated
Standard library bundling	✅ Complete
LSP server implementation	✅ Diagnostics, hover, go-to-definition, references, symbols, completion, formatting, rename, semantic tokens (full + range), code actions (quick fixes) — semantic token deltas and signature help not implemented
gRPC service layer	✅ Complete (parse, symbols, diagnostics, runtime, verification, conversion, edit and Query RPCs), served as gRPC, gRPC-Web and the Connect protocol on one port
Public Go API (client/opensysml)	✅ Complete for its v1 scope: parse, diagnostics, symbols, evaluation, instantiation and capability negotiation, answered in process or over Connect, with the edit API, conversion, verification, behaviour execution and Query out of scope (client/opensysml/README.md)
Python client library	✅ Complete for the RPCs that exist (connection lifecycle, parse/symbols/eval/instantiate/execute, constraint/requirement/satisfaction/calc verification, conversion, edits, Query, IPython hooks, DataFrame)
Rust client library	🚧 Blocking v1 client for parse, diagnostics, symbols, evaluation and instantiation; see the Rust client README
Java client library	✅ Complete for its v1 scope, with the remaining scope stated explicitly: connection lifecycle, parse/symbols/eval/instantiate and capability negotiation, with the edit API, conversion, verification, behaviour execution and Query out of scope. Connect protocol over the JDK's own HTTP client, so no gRPC or Netty reaches a host application (clients/java/README.md)
Node/TypeScript client library	✅ Complete for the same v1 scope, in Node and the browser, over the Connect protocol with protobuf bodies and no native addon; values arrive as discriminated unions (clients/node/README.md)

Measured against the pinned reference (PILOT_TAG=2026-07, artifact 0.61.0). Every number below is generated by make docs-counts from the committed baselines and gated; none of them is typed in by hand.

• Corpus agreement: 332 of 357 files agree diagnostic-by-diagnostic; 20 diagnostics are ours alone and 45 the reference's alone, and the first number must be read by root: our diagnostics against the reference's own corpora fell while our non-standard-notation warnings on our own example models rose (differential, go run ./cmd/pilot-diff).
• Declared-diagnostic silence: of the 511 declared errors rows in the reference's own Xpect suites, we report nothing for 0. 244 we report word-for-word; 248 wording-only and 7 location-only differences are agreement in substance and are not counted as gaps; 0 more we report as a warning and 2 elsewhere in the file (Xpect oracle, go run ./cmd/pilot-xpect).
• Scope agreement: 230 of 230 declared scope assertions match exactly (same source).
• Permissiveness gaps: of 120 invalid models we wrote ourselves, the reference rejects 2 that we accept by default, and 118 both reject; 2 further cases agree only when we are asked strictly. We authored every one of these cases ourselves, so the denominator measures the reach of our own corpus and not our conformance; agreement reached only under an opt-in strict mode is weaker evidence than agreement by default (rejection oracle, go run ./cmd/pilot-reject).
• Declared errata: the registry declares 3 defect(s) in the published reference material — 1 with a specification-derived correction, 2 documented without one, since no intended reading can be inferred (OMG issues, internal/errata). Every figure above is as published and stays the conformance statement; running the same oracles over the corrected text instead reports 333 of 357 files agreeing, 19 diagnostics ours alone and 45 the reference's alone, 0 declared rows we are silent on, and 0 of 120 authored cases the reference alone rejects. The corrected figures are diagnostic only: an erratum never reclassifies a divergence category, and the published corpus is never edited.
• Self-assessed surface: 146 of the tracked rules have no external referee at all — the action, state-machine and classifier-behavior rows, which the four refereed figures above cannot see, because the pinned artifact evaluates expressions but executes neither actions nor state machines.

What these numbers cannot show: the OMG corpora are demonstrations rather than an official conformance suite; the differential is one-directional, comparing the diagnostics the two implementations report on the same files; the Xpect suites are the pilot authors' test intent rather than a certification oracle; and none of these is a percentage of the specification — no global compliance figure is claimed anywhere.

Row bookkeeping: the ✅/⚠️/❌/⛔ status of each of the 760 tracked rules stays in spec compliance as a census of our own row list. It moves when rows are rewritten and does not move when an oracle does, so it is not the progress measure.

Current commit: All tests pass (go test -race ./...), builds clean (go build ./...). Test coverage: 8,361 tests and subtests (8,347 pass, 14 skip — 6 skip themselves, 8 gate on an absent OMG corpus, a live Flexo stack or an SMT solver; 4,038 top-level Test functions) covering parsers, semantics, runtime (actions, states, instances, operators, validation). Behavioral robustness: 146 golden ASTs, 261 negatives, 380 conformance cases, 118 golden traces, 256 runtime robustness cases, 15 gRPC conformance cases and 8 gRPC robustness cases. Parser coverage: 96/96 bundled library files parse cleanly — the 94 official SysML v2 standard library files and the non-normative OpenSysML Libraries/OpenSysMLMathFunctions.kerml and OpenSysML Libraries/DocumentQueries.sysml extensions. Conformance verified by stdlib_conformance_test.go. Grammar reference: OMG Xtext grammar. Behavioral execution: Calc/constraint/requirement/satisfy functional. Action/state executors handle nested invocation, control flow keywords, loop and conditional statements and the send statement (380/380 conformance cases passing). Coverage is self-assessed against the specification text and the normative library: the pinned OMG pilot implementation evaluates expressions but does not execute actions or state machines headlessly, so no external implementation currently adjudicates these rows. See spec compliance. Reference differential: 357 files compared diagnostic-by-diagnostic against the pinned OMG pilot implementation (2026-07), 332 in full agreement; every divergence is enumerated and adjudicated in the differential, reproducible with go run ./cmd/pilot-diff. Rejection oracle: the reverse direction — do we reject what the reference rejects? 120 hand-written invalid models validated by both implementations, 120 rejected by both, 0 the pinned pilot rejects and we accept; every permissiveness gap is enumerated with a reproducer and likely root cause in the rejection oracle, reproducible with go run ./cmd/pilot-reject. We wrote all 120 cases, so the count measures our coverage of the rejection surface, not our conformance — a sample, not a proof. Training examples: 100/100 files clean, gated by internal/core/model/testdata/training_examples_expected.txt. Download with ./scripts/download-training-examples.sh (from the OMG training directory). See training examples for analysis. Semantic layer: a complete implementation of runtime operators, feature chains and validation rules. See examples/semantic-layer/ for a full demonstration.

Architecture

┌─────────────────────────────────────────────────────────┐
│  Frontends: LSP Server │ Interactive REPL               │
├─────────────────────────────────────────────────────────┤
│  Workspace: Multi-file documents, incremental reindex   │
├─────────────────────────────────────────────────────────┤
│  Semantic Engine: Types, resolution, validation         │
├─────────────────────────────────────────────────────────┤
│  Execution Runtime: Expressions, instances, behaviors   │
├─────────────────────────────────────────────────────────┤
│  Parser/Lexer: Hand-written recursive descent           │
├─────────────────────────────────────────────────────────┤
│  AST: Syntax-only, immutable (semantics in side tables) │
└─────────────────────────────────────────────────────────┘

Key design principles:

• Incremental and lazy: parse immediately and resolve semantics on demand, following the precedent set by gopls and rust-analyzer
• Immutable AST: all semantic state resides in side tables keyed by node or symbol
• Pluggable validation: tiered passes (syntax → names → types → constraints)
• Separated concerns: the static analysis pipeline feeds the execution runtime

Module structure

github.com/Open-MBEE/OpenSysML
├── cmd/
│   ├── sysml-lsp/          # LSP server binary
│   ├── sysml-grpc/         # gRPC server binary (Python bindings)
│   └── sysml/              # Interactive REPL binary
├── internal/core/
│   ├── source/             # Source files, spans, line indexing
│   ├── lexer/              # Hand-written scanner
│   ├── parser/             # Recursive-descent parser
│   ├── ast/                # Syntax tree nodes
│   ├── symbols/            # Symbol tables, scope trees
│   ├── resolve/            # Name resolution (lazy, memoized)
│   ├── semantics/          # Type system, conformance, multiplicity
│   ├── passes/             # Validation passes (syntax → constraints)
│   ├── lower/              # AST → execution IR (ActionGraph/StateGraph)
│   ├── runtime/            # Execution engine (eval, instances, builtins)
│   ├── model/              # Workspace, document management
│   └── libs/               # Standard library bundling & caching
├── internal/lsp/           # LSP protocol implementation
├── internal/grpc/          # gRPC service implementation
├── internal/repl/          # REPL loop implementation
├── client/opensysml/       # The public Go API (in-process and remote)
├── clients/java/           # Java client (io.github.open-mbee:opensysml-client)
├── clients/node/           # Node/TypeScript client (@opensysml/client)
├── clients/python/         # Python client bindings (opensysml)
├── clients/rust/           # Rust client (opensysml) and its conformance runner
├── docs/                   # Design specs, architecture docs
└── testdata/               # Test fixtures (.sysml, .kerml)

Technology

• Language: Go 1.25 or later (goroutines for concurrency, a single static binary, and an established record in language servers)
• Parser: hand-written recursive descent (no framework overhead, full error recovery, sub-millisecond parses)
• Grammar source: OMG pilot Xtext grammars (SysML.xtext and KerMLExpressions)
• Spec compliance: OMG SysML v2.1 Beta 1 / KerML 1.1 (2026-07 release)
• Standard library: 94 files from SysML v2 Pilot Implementation 2026-07, byte-identical, plus the non-normative OpenSysML Libraries/OpenSysMLMathFunctions.kerml extension
• CI/CD: CircleCI for automated builds, tests and releases

Releases

Pre-built binaries for Linux, macOS, and Windows are available on the Releases page.

Supported platforms:

• Linux (x64, ARM64)
• macOS (Intel, Apple Silicon)
• Windows (x64)

Release process:

• Every commit: build and test
• Tagged releases (v*): the suite runs again on the tagged commit, then multi-platform binaries are published to GitHub Releases. Maintainer procedure: docs/project/releasing.md; what changed per release: CHANGELOG.md
• The Python client is released on its own tag (opensysml-v*), which uploads opensysml to PyPI — its version is not coupled to the core's, since it resolves a sysml-grpc binary at runtime from whichever release the caller names
• The Java client is not yet published: consume it with mvn -f clients/java/pom.xml install. The prerequisites a maintainer must obtain for a first Maven Central upload are listed in docs/project/releasing.md
• The Node client is released the same way on client-node-v*, which publishes @opensysml/client and the five per-platform packages that carry the service binary
• The Rust client is not yet published to crates.io: use a path or Git dependency, and see clients/rust/README.md and docs/project/releasing.md for the requirements of a first publish
• client/opensysml, the public Go API, requires no release of its own. It is part of this module, so a Go program pins it with go get github.com/Open-MBEE/OpenSysML@v0.3.0

Release artifacts: per-binary archives (sysml-<os>-<arch>.tar.gz, sysml-lsp-<os>-<arch>.tar.gz), opensysml-<os>-<arch>.tar.gz bundles containing both binaries, and SHA256SUMS.txt. macOS binaries are not Developer ID signed or notarized and Windows binaries are not Authenticode signed; see docs/project/macos-distribution.md.

Building

# Build all binaries
go build ./...

# Run tests
go test ./...

# Build LSP server
go build -o bin/sysml-lsp ./cmd/sysml-lsp

# Build REPL
go build -o bin/sysml ./cmd/sysml

# Build gRPC service
go build -o bin/sysml-grpc ./cmd/sysml-grpc

Python client

opensysml is a Python client library providing programmatic access to OpenSysML's parsing and runtime capabilities over gRPC.

Installation:

pip install opensysml          # from PyPI

# Or from a checkout, in development mode
pip install -e clients/python/

Quick example:

import opensysml

# Load and parse a SysML model
model = opensysml.load("vehicle.sysml")

# Evaluate expressions
result = model.eval("2 + 2")
print(result)  # 4

# Instantiate parts
instance = opensysml.instantiate("Vehicle", model_hash=model.hash)
print(instance.slots["mass"])

Features:

• Jupyter notebook integration with rich HTML displays
• pandas DataFrame integration for model analysis
• automatic service lifecycle management
• full runtime API access (evaluation, instantiation, action and state execution)

Detailed installation and usage instructions are in clients/python/INSTALL.md.

Node/TypeScript client

@opensysml/client provides the same access over the Connect protocol, for Node and the browser. It includes no native addon: installation is a standard registry fetch, and the service binary is supplied by a per-platform optional dependency.

import { loads } from "@opensysml/client";

await using model = await loads("part def Wheel { attribute radius : ScalarValues::Real = 0.3; }");
const radius = await model.eval("0.3 * 2");

Version 1 covers loading, evaluation, symbol lookup and instantiation, and negotiates against the capabilities the service advertises. It is not yet published. See clients/node/README.md for the API, the two lifecycle modes (a private child of the calling process, or an externally hosted service), the capabilities and limitations of the browser entry point, and the functionality version 1 omits.

Documentation

• The guide — install, first model, CLI, REPL, checks, behavior, saving, editors, Python
• Client libraries — the Go, Python, Node, Java and Rust surfaces, and how to choose between them
• Reference — CLI flags, REPL commands, environment, the Go and Python APIs, service transports, RDF mapping
• Internals — the pipeline, the tiers, testing and performance
• Project status — spec compliance, roadmap and releasing
• Examples — runtime demonstrations and behavioral model examples

A complete index is available in docs/README.md.

License

Apache 2.0

Contributing

The project is under active development. See CONTRIBUTING.md for build, test and contribution guidelines.

Contact

[Contact information to be added]