Simple ETL pipeline in Alloy

etl.als

// ETL pipeline

sig DataSource {}

sig Step {
  requires: set Step
}

sig Database, File extends DataSource {}
sig Extract in Step {
  from: DataSource
}

sig Load in Step {
  to: DataSource
}

fact "dag" {
  no iden & ^requires
}

fact "extracts are used" {
  all e: Extract {
    some l: Load |
      e in l.^requires
  }
}

run {some Load}