FSPB - Datapage instance structure

  Name : DCLFSPB

  Function:
  This module contains the declarative of the FSPB structure, which maps a generic datapage of a
  datafile, that is, a generic 4096 bytes page inside one of the linear VSAM data sets reserved to contain
  the SYSOUTs represented in the form of either structured or unstructured data. This structure is used
  by several  modules of data store to read / write the SYSOUT data, to interpret, clean, import,
  and export it.In the datapage structure you can find:

• A prefix, reserved to identify the sysout inside a specific datafile. Within the more significant prefix data we can list, in the real order:
  • The data page status indicator, which characterizes the data as logically deleted (leftmost bit in on)
  • The primary key of the sysout
  • The RBN (relative block number) of the first page of the SYSOUT
  • The total number of pages that constitute the SYSOUT
  • The secondary key of the SYSOUT
• The information about the real space used to store into the datapage the whole SYSOUT (if a single page can contain it completely) or a portion of it. Clearly, this length excludes the prefix and itself.

   The generic area reserved to contain a SYSOUT data portion is expressed as a generic array of single
   characters. The ability to interpret the contents of the data portion of the datapage is reserved to
   specific modules of the data store. A SYSOUT data portion inside an unstructured datafile
   is represented as an ordered list of variable-length records. However,  inside a structured datafile,
   a SYSOUT has a more complex layout, to interpret which further mapping structures are needed.