Using some clever functions within MongoDB you can implement various algorithms to create trainable learning systems within your app's database. You can apply these algorithms to systems such as spam filtering, content auto-tagging, social analytics, and other classification applications. Why build these systems using MongoDB? Other than the performance benefits of Mongo's aggregation systems, you can simplify your workflow, and improve the portability of your business logic. Finally, MongoDB offers many tools that your language or toolkit of choice may not.