Hi Chirag,
The persid field is used as a reference field by other related tables that have relationships that point to ticket tables such as chg and call_Req. Usually its used by LREL relationships between tables. For example, with attachments on tickets, the attachment_lrel table hold the relationship between the tickets and it's attachments. The attachment_lrel table references the persid of the ticket and the persid of the attachment and stores them together in a single row. The reason that the persid field is used rather than the ID field for the ticket when being referenced by another table is because the ID numbers COULD be the same for a change order and a request/incident/problem, and the persid includes the ticket type in its value such as cr:12345 or chg:12345, where as if it were to just use the ID field of each, it would be the same - "12345" so it wouldnt know which object it goes to specifically. We refer to persid values as "globally unique persistent identifier" values - meaning that the persid value on any given record is not used anywhere else in the MDB.
I hope this helps simply and provide clarification for you.
Let us know,
Thanks,
Jon I.