sap-s4-migration

name	sap-s4-migration
description	This skill supports SAP S/4HANA migration projects including approach selection (brownfield, greenfield, bluefield), SAP Readiness Check analysis, simplification item resolution, Business Partner migration, custom code remediation via ATC, Universal Journal migration, and post-cutover validation. Use when user mentions S/4HANA migration, system conversion, greenfield, brownfield, SUM, DMO, readiness check, simplification item, BP migration, custom code, ACDOCA, Clean Core, RISE with SAP, S/4HANA Cloud, selective data transition, H4S4, conversion project.
allowed-tools	Read, Grep

1. Approach Decision Tree

Q1: Keep existing configuration and historical data?
  YES  → System Conversion (Brownfield)
  NO   → New Implementation (Greenfield)
  SOME → Selective Data Transition (Bluefield / Shell Conversion)

Q2: Target deployment model?
  On-premise        → Full flexibility; custom code with restrictions
  RISE (PCE)        → Managed infrastructure; same S/4HANA functionality
  S/4HANA Cloud PE  → Clean Core only — no modifications, no ABAP CBO

Approach Comparison

Aspect	Brownfield	Greenfield	Bluefield
Data migration	Automatic (SUM/DMO)	Manual (LTMC)	Selective
Configuration	Carried over	Redesigned	Mix
Custom code	Must remediate	Can replace with standard	Must remediate
Project duration	Shorter	Longer	Longest
Risk	Medium	Lower (for processes)	High (complex)
Best for	Large existing systems	Major transformation	Demerger / consolidation

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2. SAP Readiness Check — Critical Simplification Items

FI / Accounting

Item ID	Impact	Description	Resolution
S4TWL_ACDOCA	High	Universal Journal mandatory; BSEG becomes secondary	Ensure New GL active; run Universal Journal migration
S4TWL_NEWGL	High	Classic GL not supported — New GL must be active	Activate New GL in ECC before SUM run
S4TWL_ASSETACCTG	High	New Asset Accounting mandatory; Classic AA removed	Run RAALTD01 migration report; verify parallel ledgers
S4TWL_MATERIAL_LEDGER	High	Material Ledger is mandatory in S/4HANA	Activate ML in ECC first if possible
S4TWL_BP	High	Business Partner mandatory; vendor/customer must become BP	Run BP migration (FLBPD1/FLBPD3) before conversion
S4TWL_COFI_RECONCILIATION	Medium	FI-CO reconciliation ledger removed	Ensure no open reconciliation items

MM / Logistics

Item ID	Impact	Description	Resolution
S4TWL_INVENTORY	High	Inventory tables restructured; MBEW→ACDOCA	No direct MBEW access — use CDS
S4TWL_PLANT	High	Valuation area must equal plant (1:1)	Consolidate if multiple valuation areas per plant
S4TWL_CENTRALPURCHORG	Medium	Central purchasing org restrictions	Review org structure

SD / Revenue

Item ID	Impact	Description
S4TWL_SD_CRM	Medium	CRM integration changes
S4TWL_REVENUE_RECOGNITION	High	VBREVN replaced by IFRS 15 POB approach

ABAP / Custom Code

Item ID	Impact	Description
S4TWL_COMPATIBILITY_SCOPE	High	Defines which classic APIs still supported

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3. Business Partner Migration (Mandatory for All Conversions)

Every customer and vendor must be converted to a Business Partner before go-live.

Migration Steps

Step 1: Pre-checks
  PREC_CUST  → customer readiness check
  PREC_VEND  → vendor readiness check
  Fix all errors before proceeding

Step 2: BP configuration
  BUPA_PRE_MERGE → BP grouping and number range configuration
  Define BP grouping: customer grouping / vendor grouping

Step 3: Mass creation
  FLBPD1  → vendor → Business Partner (mass conversion)
  FLBPD3  → customer → Business Partner (mass conversion)

Step 4: Verification
  BP transaction → check grouping, roles (FLVN00 / FLCU00)
  FBL1N / FBL5N → verify AP/AR still works via BP ↔ vendor/customer link

Step 5: Post-migration check
  BUPA_CHECK → Business Partner consistency check
  Reconcile customer/vendor count vs BP count

Common BP Migration Errors

Error	Root Cause	Fix
"Duplicate BP for vendor"	Vendor already linked to a BP	Check existing BP link: LFA1-BKVID
"Number range not defined"	BP grouping number range missing	BUBA → maintain number ranges
"Missing mandatory field"	BP grouping requires field not in vendor	Map fields in customizing

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4. Custom Code Remediation (ATC — ABAP Test Cockpit)

Most Common ATC Findings

Finding	Root Cause	S/4HANA Replacement
SELECT from BSEG	Table no longer primary storage	CDS: I_JournalEntryItem
SELECT * from MARA	Performance + table changes	Targeted CDS with specific fields
SELECT from MKPF/MSEG	MATDOC is new primary	CDS: I_MaterialDocumentItem
SELECT from BSID/BSAD	ACDOCA is source	CDS: I_CustomerLineItem
SELECT from BSIK/BSAK	ACDOCA is source	CDS: I_SupplierLineItem
CALL TRANSACTION	Compatibility issues	BAPI or RAP action
Logical database PNPCE	Deprecated	Direct SELECT + AUTHORITY-CHECK
Old BAdI (CL_EXITHANDLER)	Classic BAdI	New BAdI (GET BADI / SE19)
Non-Unicode strings	S/4HANA is Unicode-only	String templates |...|

ATC Check Process

1. SE80 / ATC → run check on custom package
2. Filter results: Priority 1 (blocker) and Priority 2 (high) must be fixed
3. Priority 3/4: fix before go-live but not hard blockers
4. Document findings → assign to developers → track remediation

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5. Universal Migration Timeline

Phase 1 — Discover (3–4 weeks)
  □ SAP Readiness Check → download simplification item report
  □ ATC custom code analysis → categorize findings by priority
  □ BP migration pre-checks (PREC_CUST / PREC_VEND)
  □ Fit-gap assessment: standard S/4HANA vs current processes

Phase 2 — Prepare (4–6 weeks)
  □ Solution design per simplification item
  □ BP migration configuration (BUPA_PRE_MERGE)
  □ Custom code remediation (Priority 1 + 2 items)
  □ New GL activation if not already active (ECC)
  □ Material Ledger activation if not active (ECC)

Phase 3 — Realize (12–16 weeks)
  □ DEV system conversion (SUM / DMO tool)
  □ Custom code migration and unit testing
  □ Integration testing (all modules)
  □ Parallel run for financials (if required)
  □ User acceptance testing (UAT)

Phase 4 — Deploy (4–6 weeks)
  □ QAS system conversion
  □ QAS regression testing
  □ Cutover planning and rehearsal
  □ PRD system conversion (go-live weekend)
  □ Hypercare (4 weeks minimum)

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6. Post-Migration Validation Checklist

FI:
□ Trial balance matches pre-migration (FS10N)
□ AP open items correct (FBL1N — count and amount)
□ AR open items correct (FBL5N — count and amount)
□ Asset spot check (AW01N — 10% sample of assets)
□ ACDOCA reconciliation report clean

MM:
□ Stock quantities match (MB52 pre vs post)
□ Open PO / GR / IR correct (ME2M)
□ Material prices correct (MM03 → Accounting 1)

SD:
□ Open sales orders correct (VA05)
□ Billing due list correct (VF04)
□ Credit limits migrated (FD32 / UKM_BP)

ABAP:
□ ST22: zero short dumps in first 3 days post go-live
□ SM21: no system error messages
□ Custom reports executed with expected output
□ Background jobs running on schedule (SM37)

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7. References

• references/simplification-items.md — top 30 simplification items by module with impact, resolution, effort