FICO's Falcon Assurance Navigator (FAN) is a fraud detection system that utilizes a microservices-based architecture and MongoDB as its database. The system processes transactions in queues, where each transaction is enriched with data from various services such as OCR, context creation, and decision execution engines. The analytics engines review transactions to identify outliers, and the case manager service decides whether to create a case for human follow-up based on identified issues. This complex data model is well-suited for MongoDB's document model, allowing FICO to efficiently store and process large amounts of data related to expenses and procurement.