Sparse Snapshot w/ header and detail tables

[RADSr]

So I'm putting together a ( ? ) sparse snapshot table or tables e.g. order header and order lines where I want to capture changes which happen at either the header or the line.

Individually I have it, but since header and lines can get independent AsOfDates  how do I go about joining header to line to avoid a many-to-many relationship?  

OR - am I best off just joining them in the SQL and then creating the snapshot of the new, combined header/line table and only dealing with one AsOfDate?     ( making the combination of header and line keys the key columns on the new table )