In IDMS, if you are currently positioned on the owner record of a set, what is the difference between an OBTAIN NEXT and an OBTAIN FIRST for that set?

Introduction / Context:
This question examines your understanding of navigation in an IDMS network database using DML verbs. Sets in IDMS represent one to many relationships, and you can move through the members in a defined sequence. Knowing the difference between OBTAIN FIRST and OBTAIN NEXT when you are positioned on the owner of a set is essential for predictable traversal of member records in application programs.

Given Data / Assumptions:

• You are current on the owner record of a particular IDMS set.
• That set has one or more member records connected in a defined order.
• You are issuing either an OBTAIN FIRST or an OBTAIN NEXT DML statement for that set.
• The question is about member navigation, not about changing owner currency.

Concept / Approach:
In IDMS, OBTAIN FIRST from the owner retrieves the first member in the set according to the set order, and it establishes currency on that member. OBTAIN NEXT then retrieves the next member in the chain relative to the current currency. When starting at the owner, an OBTAIN NEXT from owner typically returns the first member only if no member currency is established, but conceptually the distinction is that FIRST always positions at the first member, while NEXT moves forward from the current member. The correct option must describe this sequential behavior clearly.

Step-by-Step Solution:
Step 1: Confirm that you are current on the owner of the set and need to access member records. Step 2: Recall that OBTAIN FIRST retrieves the first member in the set sequence when starting a traversal. Step 3: Recall that OBTAIN NEXT retrieves the next member after the current member, moving forward through the chain. Step 4: Compare the answer choices and pick the one that matches these semantics without introducing confusion about owner records or random access. Step 5: Eliminate any options that claim that FIRST always returns the owner or that FIRST and NEXT are always identical.

Verification / Alternative check:
As a simple check, imagine you want to loop through all members of a set. A common pattern is to issue OBTAIN FIRST MEMBER to get the first member, then repeatedly issue OBTAIN NEXT MEMBER until there are no more members. This pattern only makes sense if FIRST and NEXT behave as described above. If FIRST always returned the owner or if NEXT skipped members entirely, this pattern would not work, which confirms the correct interpretation.

Why Other Options Are Wrong:
Option b: FIRST does not retrieve the owner record; owner currency is already established and FIRST is used to move to the first member.
Option c: FIRST and NEXT are not perfect synonyms; they behave differently depending on current currency and are designed for different points in the traversal.
Option d: There is no DML behavior where NEXT skips all members and returns a different owner; that would contradict IDMS navigation rules.

Common Pitfalls:
One pitfall is assuming that NEXT from the owner and FIRST from the owner are always interchangeable, which may be true only in some initial conditions. Another is to forget that IDMS maintains separate currency for area, record, and set, and that navigation verbs act relative to these currencies. For exam purposes, remember the conceptual intent: FIRST begins a sequence at the first member, and NEXT advances from the current member.

Final Answer:
OBTAIN FIRST retrieves the first member record in the set sequence, while OBTAIN NEXT retrieves the next member record relative to the current currency position.