Saas Erp System Design

SaaS ERP System Design

Acknowledgement: Shared by Peter Bamuhigire, techguypeter.com, +256 784 464178.

Required Inputs

Capability and permission contract

Default to read-only analysis. Change configuration, billing, identity, tenant data, infrastructure, or customer communications only with explicit authority, least-privilege credentials, tenant scope, rollback, and auditable approval. Never expose secrets or cross tenant boundaries.

Degraded mode

If production access, policy, telemetry, or authoritative records are unavailable, produce a labelled design or dry-run plan. Do not claim deployment, reconciliation, deletion, delivery, or measured outcomes; list missing evidence and verification.

Decision rules

Domain Anti-Patterns

• Applying one tenant's policy or data to another. Fix: enforce tenant scope at every boundary.
• Mutating production from an advisory request. Fix: remain read-only until authority is explicit.
• Inventing limits, prices, metrics, or compliance claims. Fix: use authoritative records or mark them unresolved.
• Shipping without rollback and audit evidence. Fix: stage and retain before/after proof.
• Treating a missing dependency as successful. Fix: name the blocked verification.

Use When

• Use when designing configurable SaaS or ERP platforms with multi-step business workflows, domain modules, approvals, auditability, pricing and entitlements, operational reporting, and tenant-specific variation. Covers domain boundaries, workflow states, extension points, and control design.

Evidence Produced

References

• Use the references/ directory for deep detail after reading the core workflow below.

Use this skill when the system must encode real business operations, not just CRUD screens. It is optimized for multi-tenant business software where configurability, correctness, and audit trails matter.

Design Priorities

• Domain correctness before UI convenience.
• Configurable behavior without tenant-specific forks.
• Explicit workflow states and approvals.
• Auditability for every material business change.
• Reporting models that do not corrupt transactional design.

System Design Workflow

1. Map Business Capabilities

Identify bounded domains such as:

• Sales and CRM
• Procurement
• Inventory and fulfillment
• Logistics network, transportation, fleet/carrier management, and warehouse execution where physical goods move across locations
• Finance and accounting
• HR and payroll
• Operations and reporting

Keep each capability distinct even if the first release ships only a subset.

2. Map Business Objects and Lifecycles

For each object define:

• Draft state
• Review or approval states
• Posted or committed state
• Reversal or cancellation path
• Audit requirements

Do not model important workflows as a single status field without state transition rules.

3. Separate Configuration from Transactions

Use distinct models for:

• Master data
• Configuration and entitlements
• Transactions
• Ledgers or audit history
• Reporting projections

Tenant-specific behavior should come from configuration, policy, or feature flags, not code forks.

4. Design Control Points

Every ERP-grade workflow needs explicit controls for:

• Permissions and separation of duties
• Approval thresholds
• Posting and locking periods
• Reconciliation and correction
• Audit log and reason capture
• Policy evaluation points and rule override governance

5. Design for Extensions

• Use module boundaries and extension points around optional verticals.
• Keep core concepts stable: party, product, location, document, ledger, user, role, workflow.
• Add industry-specific detail in modules without corrupting the core language.
• Prefer workflow composition and policy engines over tenant-specific code paths.

Modeling Rules

Workflow Rules

• Important transactions are append-only or at least auditable.
• Corrections should prefer reversal plus replacement over silent mutation.
• Status transitions must be explicit and permission-checked.
• Derived totals must be reproducible from source data.

Financial Integrity

• Never edit posted financial records in place without a traceable reversal model.
• Use document numbers, posting dates, fiscal periods, and actor attribution consistently.
• Separate operational status from accounting status when those timelines differ.

Reporting

• Operational reports can read transactional tables only while scale permits.
• Build projections or aggregates once reporting complexity or volume grows.
• Distinguish regulatory, finance, and operational reporting needs.

Cross-Module Workflows

• Define how documents, approvals, entitlements, accounting, and notifications interact.
• Ensure every cross-module workflow can be reconstructed from source events and audit history.
• Make downstream posting and reversal rules explicit before implementation.

Decision Heuristics

Use configurable policies when:

• The rule differs by tenant but the workflow concept stays the same.

Use modules when:

• The feature adds new concepts, permissions, data, or pricing boundaries.

Use approval workflows when:

• Monetary, inventory, compliance, or high-risk operational consequences exist.

Avoid per-tenant code branches unless:

• Legal or contractual obligations make configuration insufficient.

Deliverables

For major SaaS or ERP design tasks, produce:

• Domain map and module boundaries.
• Core entities and lifecycle states.
• Control and approval model.
• Entitlement and pricing model.
• Audit and reporting strategy.
• Integration map for external systems and async jobs.
• Cross-module workflow map and policy boundaries.

For ERP projects involving manufacturing, wholesale, distribution, import/export, fleet, field delivery, agriculture aggregation, or warehouse operations, pair this skill with inventory-management and load inventory-management/references/cltd-logistics-inventory-patterns.md. The ERP design should explicitly model inventory policy, in-transit stock, shipment events, carrier/fleet assignment, freight documents, customs controls where relevant, returns, claims, and logistics KPIs rather than treating fulfilment as a simple order status.

For ERP projects with billing, fees, POS, payroll, inventory valuation, grants, patient billing, school fees, donor funds, manufacturing cost, or statutory reporting, pair this skill with saas-accounting-system and load saas-accounting-system/references/accounting-bookkeeping-erp-patterns.md. The design should model GL, subledgers, control accounts, fiscal periods, posting rules, reconciliation, close, dimensions, cost centres, profit centres, tax, fixed assets, and management reporting as first-class capabilities.

References

• references/domain-modeling.md: Core entities, controls, and workflow review prompts.
• Load the external chwezi-accounting-doctrine inventory and logistics skill for inventory policy, transportation, trade documentation, and shipment exception patterns.
• ../saas-accounting-system/references/accounting-bookkeeping-erp-patterns.md: Double-entry bookkeeping, subledgers, ERP finance configuration, cost accounting, controls, reconciliations, and close patterns.
• Load modular-saas-architecture, multi-tenant-saas-architecture, and database-design-engineering when implementing the design.

Quality Standards

The design must expose authoritative records, valid transitions, approval segregation, tenant extensions, audit events, integration failures, and reporting ownership without shared-table ambiguity.

Outputs