Leshan Nang'eya

Systems

System architecture case studies

Each case study is structured as problem, decisions, system design, data model, and success metrics. I focus on clarity, resilience, and real world constraints.

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Cash intelligence platform for small and medium enterprises

A system that converts raw mobile money transactions into daily cash position, inflow and outflow trends, and business health signals. Designed for high volume businesses first, with a path toward risk and anomaly detection.

System DesignData ModelingAPIsAnalytics

Problem

Business owners rely on spreadsheets and manual summaries. They cannot see today's net cash, what is driving movement, or early warning patterns. Decisions happen late, based on incomplete data.

Users and jobs to be done

  • Owner needs daily net cash and trend direction in seconds
  • Manager needs categories and top drivers of inflows and outflows
  • Finance team needs clean exports and consistent data definitions
  • Future risk team needs anomaly ready features and audit trails

Architecture overview

  1. Ingestion service accepts statements or API feeds
  2. Normalization layer standardizes sender, receiver, amounts, timestamps
  3. Core ledger table stores immutable transactions
  4. Daily aggregates compute cash position and key metrics
  5. Insights layer produces categories, comparisons, and flags
  6. API serves dashboard and exports with role based access

Data model

  • accounts stores business entities and settings
  • transactions immutable event ledger
  • counterparties normalized people and businesses
  • categories mapping rules with override support
  • daily_metrics net cash, inflows, outflows, balances
  • audit_log traceability for edits and model updates

Key decisions

  • Ledger is append only to preserve truth
  • Derived tables are rebuildable from source
  • Category rules are explicit and overridable

Risks and controls

  • Duplication handled by idempotency keys
  • PII protected through minimal storage
  • Audit logs support compliance and debugging

Success metrics

  • Time to insight under 10 seconds
  • Daily reconciliation accuracy above 99 percent
  • Month end reporting time reduced by 50 percent

Next build steps

  1. Add a simple architecture diagram image
  2. Create sample data and show one dashboard screenshot
  3. Publish a short technical write up for trade offs and constraints
More case studies coming. Each one will include diagram, schema, and measurable outcomes.