Given a set of transformations does spark create multiple DAG's and picks the DAG by some metric such as say higher degree of concurrency or something else like the typical task graph model in parallel computing suggests? or does it simply builds one simple DAG by going through transformations/tasks in order?

I am thinking during shuffle phase there can be many ways to shuffle therefore can result in multiple DAG's and ultimately some DAG will be chosen by some metric however This is a complete guess I am not sure what exactly happens underneath spark.