Architecture Guide #24 • S/4HANA Migration Strategy

SAP S/4HANA Custom Code Migration Scoping & Package Architecture Guide

A strategic engineering guide on scoping legacy custom code, decommissioning dead assets, and designing multi-tier ADT package hierarchies for Clean Core migrations.

Interactive Architect: Automatically design your ADT package structure, generate the scoping matrix, and export the migration runbook with our In-Browser Custom Code Migration Architect.

1. The 5-Bucket Scoping Framework

When preparing an enterprise ERP landscape for SAP S/4HANA (Cloud or On-Premise), the custom code inventory typically contains hundreds of thousands of lines of ABAP code written over decades. Attempting to manually analyze every object leads to project paralysis.

Industry-standard Clean Core methodology categorizes all custom objects into 5 distinct disposition buckets:

Bucket	Criteria	Action	Typical %
1. Decommission	0 executions in SUSG / SCMON over 12 months	Delete prior to conversion or exclude from transport scope	35% - 50%
2. Quick Fix	Syntax deprecations with ADT automated fixes	Batch execute Quick Fixes via Eclipse ADT ATC view	20% - 25%
3. Tier-1 Clean Core	Strategic business logic with released API equivalents	Re-architect as RAP Business Objects and CDS View Entities	15% - 20%
4. Tier-2 Quarantine	Core logic depending on unreleased SAP objects	Wrap in Classic ABAP package and expose via Contract C1	10% - 15%
5. Key-User In-App	Simple field extensions and table UI adjustments	Replace with Custom Fields and Logic App (YY1_*)	5% - 10%

2. ADT Multi-Tier Package Hierarchy

In ABAP Cloud Clean Core, packages are not merely organizational folders; they are architectural boundaries enforced by the compiler. The ABAP Language Version must be explicitly configured at the package level:

Root Package (`ZPROJECT_ROOT`): Defines the namespace and common transport layer.
Tier-1 Package (`ZPROJECT_TIER1`): Set to ABAP Language Version = 'ABAP Cloud'. Code here can ONLY call SAP Released APIs (Contract C1) and objects exposed via Package Interfaces.
Tier-2 Package (`ZPROJECT_TIER2`): Set to ABAP Language Version = 'Standard ABAP' (permitted in Private Cloud and On-Premise). Contains quarantined wrappers that call classic BAPIs/tables.
Package Interfaces: Enforce visibility. Tier-1 cannot call internal Tier-2 objects unless explicitly declared in the Tier-2 Package Interface.

3. Automated Decommissioning via SUSG

Rule #1 of Migration: The cleanest custom code is code that does not exist. Do not remediate code that has not been executed by any business user in the past 12 months.

Activate Source Code Monitor (SCMON) in Production and aggregate data monthly via transaction SUSG. Load the aggregated usage data into the SAP BTP Custom Code Migration App to automatically filter out unused packages.

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