The tables named 
STOREDSECT.DBEFileSetName are the stored section tables for
DBEFileSetName.
These tables are created when you issue the statement
GRANT SECTIONSPACE ON DBEFileSet.
Even with DBA authority, you have limited access to the
STOREDSECT.DBEFileSetName tables.
You cannot access these tables directly, but you can use 
ALTER TABLE or UPDATE STATISTICS on them, as explained
in the section "Using the System Catalog"
earlier in this chapter.
You can see entries for the STOREDSECT.DBEFileSetName 
tables in SYSTEM.TABLE.