Question

Below is part of my work so far. I’m getting cycles and both ways connections in between my Lines and single connections from Messages to Lines for some reason. I don’t see why there are never more than one message to line connections. My facts are probably (most likely) a little wrong. Thanks for the help.

some sig Line{  
    nextLine: some Line,
}

sig Message{
    formedOfLines: Line,
}
fact MessageHasMoreThan1LineHasNextLine{
    all m:Message|#m.formedOfLines>1 implies #m.formedOfLines.nextLine>0
}
fact NoNextLineIsSelf
{
   all l1,l2:Line | l1=l2 implies l1.nextLine!=l2
}
fact LineBelongsToSomeMessage
{
    all l:Line | l in Message.formedOfLines
}

Answer 1

Your model allows each Line to have multiple nextLines, which might not be your intention. That’s why your NoNextLineIsSelf fact doesn’t actually prevent loops, because l.nextLine != l can be true if l.nextLine contains more than one Line and one of them is l. You can rewrite that fact to

all l: Line | l !in l.nextLine

to forbid all loops.

To forbid “two-way connections” between lines, you can write something like

all disj l1, l2: Line | l2 in l1.nextLine implies l1 !in l2.nextLine

(I’m not sure which one of your facts was supposed to do that)

If you want a Message to have more than 1 line, you should change the multiplicity of the formedOfLines to set, i.e.,

sig Message {
  formedOfLines: set Line
}