needsysml-sd Directive¶

The .. needsysml-sd:: directive generates a Sequence Diagram for a given interaction definition (conventionally an ActionDef that represents the interaction). A companion .. needsysml-sd-svg:: renders the same diagram as inline SVG.

Usage¶

.. needsysml-sd:: <interaction-id>
   :scale: <N>%
   :align: <left|center|right>

.. needsysml-sd-svg:: <interaction-id>
   :align: <left|center|right>

Lifelines¶

Each participant is declared as a lifeline need:

.. lifeline:: driver_ll
   :id: LIFELINE-001
   :definition: AD-001
   :represents: ACTOR-001

The :represents: field optionally points at the Part, Actor, or Subsystem the lifeline represents.

Messages¶

Messages connect two lifelines:

.. message:: turn_key
   :id: MSG-001
   :from_lifeline: LIFELINE-001
   :to_lifeline: LIFELINE-002
   :message_kind: sync

The :message_kind: enum:

Combined fragments¶

Messages sharing a :fragment_group: value render inside a single combined-fragment frame. The first message’s :fragment_kind: and :fragment_guard: are used as the frame header.

.. message:: crank
   :id: MSG-002
   :from_lifeline: LIFELINE-002
   :to_lifeline: LIFELINE-003
   :message_kind: async
   :fragment_group: F1
   :fragment_kind: alt
   :fragment_guard: key_position == 'start'

Supported :fragment_kind: values: alt, opt, loop, par, neg, critical (enum-validated by sphinx-needs).

How It Works¶

The PlantUML directive wraps .. needuml:: with :config: sysml_sd and emits native PlantUML sequence syntax (participant, message arrows, alt/opt/loop blocks). The SVG companion lays out lifelines as vertical columns with dashed timelines and stacks message arrows by row, wrapping each fragment_group in a labelled rectangle.

Clickable Links¶

PlantUML variant: each participant carries a [[<docname>.html#<id>]] link active when plantuml_output_format = "svg". SVG variant: each lifeline and each message label is wrapped in a native <a href>.