Basic OMS System

A simpler order-management system template for interviews. This page keeps the finance OMS business flow, but frames it as a reusable system design blueprint: capture the order, validate it, route it, track execution, allocate fills, and complete downstream processing cleanly.

Template
Core Role

A basic OMS is the system of coordination between decision-making and execution. It accepts instructions from an upstream user or portfolio system, enforces business and risk rules, routes orders to the right execution venue, tracks fills in real time, and produces the downstream records needed for allocation, confirmations, reconciliation, and audit.

Lifecycle
01
Capture
Order enters from UI, API, PMS, or batch upload with account, instrument, side, and quantity.
02
Validate
Check instrument permissions, account state, position limits, buying power, and compliance rules.
03
Route
Select broker, EMS, or venue path using order type, urgency, and market or liquidity constraints.
04
Execute
Track acknowledgements, partial fills, cancel-replace flows, and final status changes in real time.
05
Allocate
Distribute fills across client accounts, sleeves, or portfolios using defined allocation logic.
06
Confirm
Persist confirmations, downstream events, reconciliation records, and audit history for settlement and reporting.
System Context
PMS
Portfolio / Upstream Decisioning
Creates or proposes orders based on strategy, target exposure, or manual trader input.
⟷
OMS
Order Management Core
Validates, routes, tracks status, owns order state, and feeds downstream accounting and compliance.
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EMS
Execution / Venue Layer
Optimizes live execution, venue choice, market connectivity, and intraday execution tactics.
Core Modules
Order State
  • Create, amend, cancel, and version orders safely
  • Track open, partially filled, filled, rejected, and canceled states
  • Persist an immutable audit trail of every transition
Risk and Rules
  • Pre-trade controls for account restrictions and exposure limits
  • Market-specific business logic such as allowed order types
  • Post-trade checks for reconciliations and exception handling
Downstream Events
  • Execution reports and fill updates
  • Allocation and booking events for client accounts
  • Confirmation, reporting, and settlement handoff messages
Business Logic To Name-Drop
Pre-Trade Logic
  • Buying power and position checks before routing
  • Instrument eligibility by account, market, or client mandate
  • Duplicate-order and stale-price protection on the capture path
  • Validation rules differ for market, limit, stop, and algo orders
Post-Trade Logic
  • Partial fills update remaining quantity and average price
  • Allocations fan out one parent fill into many account bookings
  • Reconciliation detects breaks between OMS, broker, and custodian
  • Audit and reporting flows should be append-only and traceable
Reference Architecture
Sync Path
  • API / UI receives order intent
  • OMS service validates order and stores canonical state
  • Risk or compliance service approves / rejects
  • Routing service sends the order to EMS or broker connectivity
Async Path
  • Execution reports arrive through FIX or venue adapters
  • Event bus fans out updates to allocations, notifications, and reporting
  • Ledger / booking service creates downstream records
  • Reconciliation and settlement jobs process later lifecycle stages
What Good Sounds Like In An Interview
Ownership
  • The OMS owns the canonical order state
  • The EMS optimizes execution, but should not replace OMS state
  • Reference data and account constraints should be validated early
Correctness
  • Idempotency matters for duplicate execution reports
  • Every state transition should be traceable and replayable
  • Partial fills and cancel-replace paths are core, not edge cases
Scale
  • Use async fan-out for downstream processing and reporting
  • Cache read-heavy reference data, but not the source-of-truth state machine
  • Separate low-latency order handling from slower batch reconciliation work
Why OMS Matters
STP
Straight-through processing reduces manual breaks
FIX
Connectivity standard for execution and status updates
T+1
Settlement pressure drives clean downstream automation
360°
Visibility across orders, fills, allocations, and audit state