peterbamuhigire/saas-erp-system-design

SaaS ERP System Design

<!-- dual-compat-start -->

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.
• The task needs reusable judgment, domain constraints, or a proven workflow rather than ad hoc advice.

Do Not Use When

• The task is unrelated to saas-erp-system-design or would be better handled by a more specific companion skill.
• The request only needs a trivial answer and none of this skill's constraints or references materially help.

Required Inputs

• Gather relevant project context, constraints, and the concrete problem to solve; load references only as needed.
• Confirm the desired deliverable: design, code, review, migration plan, audit, or documentation.

Workflow

• Read this SKILL.md first, then load only the referenced deep-dive files that are necessary for the task.
• Apply the ordered guidance, checklists, and decision rules in this skill instead of cherry-picking isolated snippets.
• Produce the deliverable with assumptions, risks, and follow-up work made explicit when they matter.

Quality Standards

• Keep outputs execution-oriented, concise, and aligned with the repository's baseline engineering standards.
• Preserve compatibility with existing project conventions unless the skill explicitly requires a stronger standard.
• Prefer deterministic, reviewable steps over vague advice or tool-specific magic.

Anti-Patterns

• Treating examples as copy-paste truth without checking fit, constraints, or failure modes.
• Loading every reference file by default instead of using progressive disclosure.

Outputs

• A concrete result that fits the task: implementation guidance, review findings, architecture decisions, templates, or generated artifacts.
• Clear assumptions, tradeoffs, or unresolved gaps when the task cannot be completed from available context alone.
• References used, companion skills, or follow-up actions when they materially improve execution.

References

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

<!-- dual-compat-end -->

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
• 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.

References

• references/domain-modeling.md: Core entities, controls, and workflow review prompts.
• Load modular-saas-architecture, multi-tenant-saas-architecture, and database-design-engineering when implementing the design.