code: def parse_schema_files(files):
      
      f_dict = {}
      for f in files:
          root, ext = os.path.splitext(f)
          if ext != ".sql":
              continue
          vto, vfrom = os.path.split(root)
          vto = os.path.split(vto)[1]
          if is_schema(vto) and is_schema(vfrom):
              f_dict[f] = (vfrom, vto)
      return f_dict
docs: Parse a list of SQL files and return a dictionary of valid schema
      files where each key is a valid schema file and the corresponding value is
      a tuple containing the source and the target schema.