1. A system for performing business activity monitoring, the system comprising: an event source configured to generate a plurality of events related to a particular business activity and send the plurality of events to a database; the database configured to store data from each of the plurality of events; and a business activity monitor system in communication with the event source and the database, the business activity monitor system comprising one or more processors and one or more memory devices having stored thereon instructions, which when executed by the one or more processors, cause the one or more processors to: intercept a first event in the plurality of events sent from the event source to the database; wherein the first event comprises a correlation ID and a first data set; determine that the event represents a new business flow; create a business flow object to store data associated with the business flow; intercept a second event in the plurality of events sent from the event source to the database; wherein the second event comprises the correlation ID and a second data set; determine that the second event is part of the business flow based on the correlation ID; store an aggregate value of a measured indicator related to the particular business activity, wherein: the aggregate value of the measured indicator is calculated using the first data set and the second data set; and the aggregate value of the measured indicator is stored in the business flow object at the business activity monitor system; calculate a value of a complex indicator, wherein the value of the complex indicator depends on the aggregate value of the measured indicator; intercept subsequent events sent from the event source to the database over time that include the correlation ID, and thereby incrementally update the aggregate value of the measured indicator and the value of the complex indicator, wherein the value of the complex indicator is updated in real time; and propagate at least part of each intercepted event to the database for storage.