BPMN / Business Process

About BPMN diagrams

A BPMN diagram documents a business process — the activities, decisions, events, and message exchanges that happen across roles, departments, and systems. It's the dominant notation in enterprise BPM, ISO-9001 / SOX audits, and process-mining tooling. The only official serialization is BPMN 2.0 XML, which is verbose and hostile to LLM generation; Schematex provides a compact text DSL that produces a conformant visual subset.

Schematex implements OMG BPMN 2.0.2 / ISO/IEC 19510:2013 for the elements that real-world business analysts actually draw: pools, lanes, events (start / intermediate / end with none / message / timer triggers), activities (tasks with markers + collapsed subprocesses), gateways (XOR / OR / AND / event-based), and sequence / conditional / default / message flows.

Note — Schematex is a rendering library, not a process-execution engine. There is no token simulation, no XML round-trip, and no DI (Diagram Interchange) layer. v0.1 covers the visual subset most teams use; boundary events, expanded subprocesses, and the rare trigger types (cancel / compensation / escalation / signal / link) are deferred to v0.2+.

1. Your first BPMN diagram

Three sections: a one-line bpmn header, one or more pool { … } blocks, and a flows block. Inside each pool you put lane { … } blocks, and inside each lane you list flow objects as id: kind "label".

Every flow object starts with an id, a colon, the kind, an optional sub-keyword (trigger / marker / gateway type), and a quoted label. Ids are referenced by flow lines.

2. Pools and lanes

A pool represents one participant — an organisation, a department, or a system. A lane subdivides a pool into roles. The pool label is rendered rotated 90° on the left edge of a horizontal pool.

pool "Customer" blackbox          // black-box pool — no internal flow
pool "Bank" {
  lane "Clerk" { … }
  lane "Underwriter" { … }
}

A black-box pool is a participant whose internal process you don't model — typically an external customer or partner. Black-box pools must contain zero flow objects (Schematex enforces this in the parser).

Sequence flow (-->) is not allowed to cross pool boundaries. Use a message flow (~~>) for cross-pool communication.

3. Events

Events are circles. Stroke weight encodes lifecycle role:

The optional trigger keyword adds an inner glyph. v0.1 supports the three most common triggers — none (no glyph), message (envelope), and timer (clock face):

A: start                       // none-trigger
A: start message "Inbound"     // message-catch (unfilled envelope)
T: intermediate timer "60 min" // timer (clock face)
F: end "Done"

Filled glyph = throw, unfilled glyph = catch. Schematex picks the right fill automatically based on event kind.

4. Activities — tasks and subprocesses

Activities are rounded rectangles. The two v0.1 forms are task and a collapsed subprocess (the + marker indicates expandable detail):

B: task "Generic abstract task"
U: task user "User decides"
S: task service "API call"
SE: task send "Send email"
RE: task receive "Wait for reply"
M: task manual "Hand-stamp the form"
SC: task script "Run rule engine"

X: subprocess "Verify identity" collapsed

The task marker (small icon top-left) communicates who or what performs the work — a person (user), a software service (service), an outbound message (send), an inbound wait (receive), an out-of-system manual step (manual), or an automated script (script). When in doubt, omit the marker — it defaults to abstract.

5. Gateways

Gateways are diamonds. The inner glyph encodes branching semantics:

Schematex uses Bruce Silver's X glyph for XOR by default — that's the convention real BPMN audits expect. Most diagrams use XOR (data branch) and AND (parallel split / join); OR is rare and event-based mostly appears in race-condition models.

6. Connectors

Four connector types. Three of them stay inside a pool; only message flow is allowed to cross pool boundaries.

A --> B                  // sequence flow (default)
G --? "yes" --> C        // conditional sequence (label is a guard)
G --* "default" --> D    // default flow (one per gateway, max)
"Customer" ~~> A : "Submit application"   // message flow
E ~~> "Customer" : "Notify approval"      // message flow back

• --> is the workhorse — solid line + filled triangle arrowhead.
• --? "label" --> adds a small unfilled diamond at the source. Use it when leaving an activity directly on a guarded outcome. (At a gateway, the conditional label suffices; the diamond glyph isn't drawn.)
• --* "label" --> adds a slash mark at the source. One default flow maximum per gateway — Schematex enforces this.
• ~~> is dashed with an open arrowhead and a small unfilled circle at the source. Source or target may be a quoted pool name (for black-box participants) or an object id.

7. Validation

The parser refuses diagrams that violate BPMN semantics, with line-numbered errors:

These checks fire during parse, so an LLM gets a usable signal before the layout pass.

8. Larger example — pizza order with black-box customer

A canonical BPMN tutorial: an external customer (whose process we don't model) places an order with a pizzeria split into Clerk / Chef / Delivery lanes, with a rework loop on the chef's quality check.

The rework loop (D --> C) creates a back-edge that the layout's cycle-break detects via DFS — the longest-path layering then proceeds on the forward DAG so columns stay sensible.

9. Limitations of v0.1

These are deferred to a later release. If your diagram needs one, file an issue with the use case:

• Boundary events — events attached to an activity edge (timer, error, escalation, compensation). Currently you have to model the boundary as a free-floating intermediate event with manual flows.
• Expanded subprocesses — collapsed subprocess works; expanded inline blocks (subprocess "X" { … }) are deferred.
• Rare event triggers — error / escalation / cancel / compensation / signal / link / conditional / multiple / parallel-multiple. Use none or message as a placeholder.
• Transaction / call activities — render as normal tasks for v0.1.
• Loop and multi-instance markers — bottom-center activity glyphs; deferred.
• Artifacts — data object / data store / group / text annotation. Deferred.
• BPMN 2.0 XML import / export — out of scope. Schematex computes layout from DSL; no DI layer to round-trip.