arangosh> a1 = db.example.insert({ a : 1 });
{ 
  "error" : false, 
  "_id" : "example/494938275", 
  "_rev" : "494938275", 
  "_key" : "494938275" 
}
arangosh> a2 = db.example.replace("example/3903044", { a : 2 });
{ 
  "error" : false, 
  "_id" : "example/3903044", 
  "_rev" : "495134883", 
  "_key" : "3903044" 
}