IMS DB/DC interview questions

What is PSB and PCB?

PSB is Program Specification Block which is a collection of one or more PCBs.
PCB is Program Control Block which represents the application program's view of the database.

What is PROCOPT?

PROCOPT is processing option defined in PCB, which specifies the operations that can be performed on the database. Different PROCOPTs that can be used are

G - Get segment from DB

I - Insert segment into DB

R - Replace segment
D - Delete segment

A - All the above operations
LS - Load Sequential in GSAM (HIDAM)
GS - Get Sequential in GSAM

What is SSA?

SSA is segment search argument. It is used to retrieve a particular segment or segment type from the DB.

What are qualified and unqualified calls?

IMS call with SSA is called qualified call. IMS call without SSA is unqualified call.

What are qualified and unqualified SSAs?

SSA which contains only the segment name is Unqualified SSA. SSA which contains segment name, field name, relational operator and search value for the field name is qualified SSA.

What are command codes?

Command codes are used along with SSAs to perform additional operations. Common command codes used are 

'P' - used to set parentage on a particular segment

'D' - used for path calls, to retrieve the entire hierarchical path

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