Component diagrams

A component diagram shows a system’s parts, the interfaces they offer and need, and how they are wired. It is drumlin’s default: a file with no diagram line is a component diagram. Write the header anyway when you want a title. The notation follows UML 2.5.1 clauses 11.2, 11.3 and 11.6. The full syntax is in the grammar reference, and examples come from real kinds of system.

diagram component "Title"
direction right

The default direction is right, with direction down for layered pictures. See File basics.

Parts

Declare a component by name, quote names with spaces and give them a short alias with as. A block nests components, and a <<stereotype>> shows as a keyword. Group loosely related parts in a package, which is a folder around them.

diagram component "Parts and grouping"

package "Platform" {
  component "Request Router" as router <<service>> {
    component Parser
    component Dispatcher
    Parser --> Dispatcher
  }
  component "Orders DB" as db <<database>>
  router --> db
}

Connecting parts

A connector joins two elements. --> is a solid connector with an open arrow and ..> is a dashed dependency. Text after : becomes the label.

diagram component "Connectors"

component Producer
component Consumer
component Metrics
Producer --> Consumer : batches
Producer ..> Metrics : reports

Interfaces

Inside a component, provides and requires declare interfaces. You name them and drumlin draws them. If an interface has both a requirer and a provider of the same name, drumlin wires them. What it draws depends on where the two ends are declared, as UML requires:

Ends	What is drawn
Two simple ports (one interface each)	Ball-and-socket: the ball seated in the socket
A port with several interfaces at either end	A plain connector named after the interface
Anything else (a component with no port at one end)	Socket and lollipop kept apart, joined by a dashed dependency arrow

An interface with no partner stays a stub on the boundary: a lollipop if it is provided, a socket if it is required.

diagram component "Matched by name, no ports"

component Client { requires IOrders }
component Server { provides IOrders, IHealth }

Ports and delegation

A port is a named point on a component’s boundary, drawn as a small square. A connector from a composite’s port to a part inside it is a delegation: the port forwards to the part. Two ports with one interface each, matched by name, form a ball-and-socket.

diagram component "Ports"

component Gateway {
  port uplink requires IEvents
}

component Bus as bus {
  port in provides IEvents
  component Queue
  in --> Queue
}

Notes and layout hints

note target: text attaches a note. Layout hints such as left-of and align adjust the arrangement and never set coordinates.

diagram component "Notes and hints"

component Cache
component Store
Cache --> Store : writes through
note Cache: Entries expire after 30 seconds.

Next: Examples, or look up what any element looks like under Elements.