A real-time, processed-data streaming system that provides a stream of data messages to a data consumer, the real-time, processed-data streaming system comprising: a processing center, comprising one or more computer systems, each having one or more processors and one or more memories, which enriches received event messages to produce enriched event messages, filters enriched event messages to produce filtered, enriched event messages, and transmits a stream of filtered, enriched event messages to the data consumer; a consolidation system, comprising one or more computer systems, each having one or more processors and one or more memories, that receives event messages, buffers event messages for up to a specified amount of time, and transmits event messages to the processing center; a data-collection system, which encodes key/value pairs, extracted from received collected data, into event messages and transmits the event message to the consolidation system; and instances of instrumentation, each instrumentation instance located within a stored-instruction-based encoding of a web page, application program, control program, a user interface, or other stored-instruction-based encoding, the processing of instructions of which, on processor-controlled user appliances, results in the instances of instrumentation collecting data and initiating transmission of the data to the data-collection system, wherein the instructions further cause the instrumentation instance to: access a cookie stored within a processor-controlled user appliance to determine a last visit value; obtain a current system time; determine that a difference between the last visit value and the current system time exceeds a threshold value; and upon determining that the difference exceeds the threshold value, start a new session by storing a session start value in the cookie and setting the last visit value in the cookie to the current system time, wherein the data contained in the cookie is used by the instrumentation instance for subsequent processing of the data. a processing center, comprising one or more computer systems, each having one or more processors and one or more memories, which enriches received event messages to produce enriched event messages, filters enriched event messages to produce filtered, enriched event messages, and transmits a stream of filtered, enriched event messages to the data consumer; a consolidation system, comprising one or more computer systems, each having one or more processors and one or more memories, that receives event messages, buffers event messages for up to a specified amount of time, and transmits event messages to the processing center; a data-collection system, which encodes key/value pairs, extracted from received collected data, into event messages and transmits the event message to the consolidation system; and instances of instrumentation, each instrumentation instance located within a stored-instruction-based encoding of a web page, application program, control program, a user interface, or other stored-instruction-based encoding, the processing of instructions of which, on processor-controlled user appliances, results in the instances of instrumentation collecting data and initiating transmission of the data to the data-collection system, access a cookie stored within a processor-controlled user appliance to determine a last visit value; obtain a current system time; determine that a difference between the last visit value and the current system time exceeds a threshold value; and upon determining that the difference exceeds the threshold value, start a new session by storing a session start value in the cookie and setting the last visit value in the cookie to the current system time,