How to correct PlantUML Line Path

Question

I created this diagram using the following code. But as you can see, the lines going from (Cancel Order) and (Place Order) to (Publisher) decide to take a terribly rounded path to get their, instead of going straight to the right and then down to publisher. I tried using manual direction commands like "-down" but none of them seemed to help. Does anybody know how to fix this?

And here is my code. I appreciate any help. Thank you.

@startUML EBook Use Case Diagram
left to right direction
Actor Customer as customer
Actor EBook as ebook
Actor Publisher as publisher
rectangle "Book Catalogue" {
    together {
        Actor "Book Database" as bookLog
        (Retrieve Information) as getBook
        customer -- getBook
        getBook -- ebook
        getBook -- bookLog

        (Update Catalogue) as updateCatalogue
        ebook -- updateCatalogue
        updateCatalogue -- bookLog
    }

    together {
        (Place Order) as order
        customer -- order
        order -- ebook
        order--publisher

        (Cancel Order) as cancelOrder
        customer -- cancelOrder
        cancelOrder -- ebook
        cancelOrder--publisher
    }
}

(Ship To EBook) as shipEBook
shipEBook -- publisher
(Ship To Customer) as shipCustomer
customer -- shipCustomer
ebook -- shipEBook
shipCustomer -- ebook

(Return to EBook) as returnCustomer
(Returnto Publisher) as returnPublisher
customer -- returnCustomer
returnCustomer -- ebook
ebook -- returnPublisher
returnPublisher -- publisher

@endUML

Solution 1

To make a connection less important in the layout, use [norank], e.g., a -[norank]-> b

Solution 2

There are some tricks that you can try, listed below. The layouting itself is performed by GraphViz (dot layouting iirc), and GraphViz simply does this sometimes. Graph layouting is a NP-complete problem, so algorithms usually take harsh shortcuts.

Typical workarounds that I've seen or used include:

• adding hidden lines a -[hidden]- b
• extending the length of a line a --- b (more dashes, longer line)
• specifying preferred direction of lines (a -left- b)
• swapping association ends (a -- b → b -- a)
• changing the order of definitions (the order does matter... sometimes)
• adding empty nodes with background/border colors set to Transparent

So if you really want to have a nice layout, you'll need to put some elbow grease in, but keep in mind that the layout will be still brittle -- if you add/remove items, you might need to redo it again.

Solution 3

Try the options suggested by @Peter Uhnak along with linetype :

skinparam linetype polyline
skinparam linetype ortho

Give better options for lines. Using ortho - (Here)

you will get -

Solution 4

If anyone wants to know a more specific, put probably much more useless answer, here is what I did in the end.

    order -down- publisher
    publisher -[hidden]up- order

so for some reason adding the duplicated command both ways solves it.

Solution 5

All these good answers are compiled and referenced in the semi-official Hitchhiker’s Guide to PlantUML. See the Layout section.

Not sure how it was 3 years ago, but it's probably now a better starting point for PlantUML tweaks than SO.

View more solutions

Comments

[FunkyBaby]

how do you make the picture so clear? did you first export to svg and then convert to png?

[aSamWow]

hey, I just did export to image (png probably?) with the vscode plant uml extension. I don't use vscode or plantuml anymore, so I can't be of much help, sorry.

[aSamWow]

Good idea, it does fix the problem, but Ortho lines mess up labels in plant UML so I try to avoid them for more complex diagrams.

[6pi]

I would like to point out the use of together done by @aSamWow. I didn't know this command before but I just successfully use it like following : together group1 { class a class b } together group2 { class c class d } group1 -[hidden]- group2

[kinjelom]

"label positioning wrong in linetype ortho" - please vote for it: github.com/plantuml/plantuml/issues/149

[fkleedorfer]

My goal with this answer is to document an undocumented PlantUML feature with minimal cognitive load in a place where related features are nicely listed (and accepted as the answer). Users of PlantUML will appreciate norank in the context of this question.

[aSamWow]

I appreciate this. I never knew about the norank option! @fkleedorfer

[Fred]

I didn't know about the line length feature! Thank you very much!

[Uwe Geuder]

> for some reason: I guess the reason is that every edge adds weight. In Graphviz one can specify weight of edges, but I have not found a way to do it in PlantUML.