Diagram: Sequence¶

A UML sequence diagram maps ordered message arrows over lifelines. Each actor is placed left-to-right at the top. A dashed lifeline drops down. Activation bars, activity dividers, and notes can be layered in.

Minimal example¶

import engrapha_notes as en
import engrapha_diagrams as ed

seq = ed.SequenceDiagram(width=400, height=220, caption="Fig 2: TCP Handshake")

seq.actor("cl", "Client")
seq.actor("srv", "Server")

seq.message("cl", "srv", "SYN")
seq.activate("srv")
seq.divider("Internal processing")
seq.message("srv", "cl", "SYN-ACK", arrow="dashed")
seq.deactivate("srv")

en.add(seq.as_flowable())
en.build_doc("seq.pdf")

Arrow styles¶

seq.message(src, dst, "data", arrow="solid")          # default
seq.message(src, dst, "data", arrow="dashed")
seq.message(src, dst, "data", arrow="solid_open")     # open triangle
seq.message(src, dst, "data", arrow="dashed_open")    # open, dashed

Self-messages¶

from_id == to_id renders as a small loop above the lifeline:

seq.message("srv", "srv", "retry(3)")

Activation bars¶

Wrap activity in activate / deactivate:

seq.activate("db")
seq.message("app", "db", "SELECT ...")
seq.deactivate("db")

Divider¶

Insert a time-divider label across the width of the canvas:

seq.divider("— Authentication —")

Auto layout¶

Nodes are evenly spaced automatically. Override x, y only when you need manual control. When left as None, each actor is evenly distributed:

seq.actor("a", "Alpha")
seq.actor("b", "Beta")
seq.actor("c", "Gamma")

If you want multi-column alignment, just specify explicit coordinates:

seq.actor("a", "Alpha", x=120, y=200)
seq.actor("b", "Beta", x=280, y=200)

Parameters reference¶

Parameter	Default	Purpose
`width`	`400`	Canvas width
`height`	`200`	Canvas height
`theme`	—	Vector theme
`row_height`	auto	Vertical spacing
`actor_margin_top`	`20`	Top margin
`margin`	`120`	Side margins
`arrow`	`"solid"`	`solid`, `dashed`, `solid_open`, `dashed_open`