Extended By IBMiSkills

Okay, let’s focus just on “Extended By” in Synon/2E (Cool:2E).

🧾 What Does Extended By Mean?

In Synon/2E, an “Extended By” relationship is:

A 1-to-1 relationship between two files.
The child file extends the parent file by adding more fields.
Both files share the same primary key.
A record in the child file cannot exist without its corresponding parent record.

👉 Think of it as splitting a record into two files: the parent holds base data, the extension holds optional or additional data.

CUSTOMER file → stores basic customer info:
- CUSTOMER_ID
- NAME
- ADDRESS
CUSTOMER_EXT file → adds extra details:
- CUSTOMER_ID (same key)
- LOYALTY_POINTS
- PREFERRED_LANGUAGE

CUSTOMER_EXT *is extended by* CUSTOMER

So:

Cardinality: 1-to-1 (not 1-to-many like Is Owned By).
Access Path: Always keyed by the parent’s primary key.
Referential Integrity: Parent must exist first. If parent deleted, extension is deleted too.
Usage:
- Separate infrequently used fields.
- Store sensitive info separately.
- Bypass record-length limits in large files.

Relationship	Cardinality	Purpose
Is Owned By	1-to-Many	Child/transactional records (e.g., CUSTOMER → ORDERS)
Is Extended By	1-to-1	Extra attributes or optional data (e.g., CUSTOMER → CUSTOMER_EXT)

Very common when a base master file (like POLICY, MEMBER, PROVIDER) is extended with a secondary file for additional attributes.
Keeps the main file lightweight while still linking extra fields tightly to it.