Fusionbeginner
Oracle Fusion Cloud SaaS Architecture Overview
Understand the fundamental architectural differences between Fusion Cloud SaaS and traditional on-premise EBS
Fusion is not EBS in the cloud. It is a different technology stack, a different extensibility model and a different operating model.
Moving from EBS to Fusion Cloud is like moving from owning and maintaining your own car (buying, fueling, servicing, upgrading it yourself) to using a subscription car service where the provider handles all maintenance and periodically upgrades your vehicle's features — you lose some control over timing, but gain massive reduction in operational burden.
Key Concepts
1
Getting that across is what the question is for.
2
Three things changed.
EBS Fusion
Forms and OAF ADF
you patch, when you like Oracle patches, quarterly
customise with code configure, in a sandbox3
The quarterly cycle changes the job. Every customer on a pod moves to the new release on a fixed date.
You do not choose when, and you cannot decline.
4
EBS plan a patch, test it, schedule downtime, apply it
Fusion Oracle applies it. You regression-test beforehand,
on a test pod that gets the update first.5
So the work moves from applying patches to testing what is coming. That is the practical difference for a
consultant, and it is a real shift in what the role involves.
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Feature opt-in softens it. Many new features arrive disabled and are enabled when you choose — until a
later release makes them mandatory.
7
That gives you a window rather than a veto. Tracking which opted-out features are about to become
compulsory is part of the quarterly routine.
8
Business Units replaced Multi-Org. The idea is similar — a processing and security boundary — and the
implementation is not, so EBS multi-org knowledge transfers as a concept rather than as configuration.
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Extensibility is configuration, not code.
EBS Forms Personalization, CUSTOM.pll, custom PL/SQL
Fusion Page Composer, Application Composer, sandboxes10
A sandbox is the mechanism that makes this workable: changes are made in an isolated copy, tested, and
published. Nothing is edited in place in production.
11
And the underlying reason for all of it. Oracle cannot patch a multi-tenant system quarterly if
customers have modified the code. So the extension points are constrained to things Oracle can carry
forward automatically.
12
That constraint is the trade. You give up the ability to change anything, and in return you stop owning
upgrades — which for most organisations was the expensive part.
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What the interviewer is probing.1. "What changes for a developer moving from EBS to Fusion?" Probing: the honest shift.
Stalls: "Nothing much." Moves up: no database access and no custom PL/SQL in the application —
extension happens through composers, sandboxes, REST APIs and BI Publisher.
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2. "What is the update model?" Probing: the operational reality. Stalls: "You choose."
Moves up: quarterly updates applied by Oracle on their schedule, so regression testing is a
recurring commitment, not a project.
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3. "Where does custom logic live now?" Probing: the architecture. Stalls: "In Fusion."
Moves up: in Application Composer groovy for light cases, and otherwise outside in OIC or a PaaS
service calling REST APIs.
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4. "What is the main constraint to flag to a business?" Probing: the advisory angle. Stalls:
"None." Moves up: you adopt the delivered process — heavy customisation is not available, so
fit-gap analysis matters far more than before.