US Patent 7441030 Delivery of continuous real-time performance data over the internet

A data retrieval engine accesses data streams (“tags”) from data sources. Each data stream preferably includes a plurality of values for a tag and a time each value was recorded. A user accesses the web server to request real-time performance data for a plurality of the tags. After authenticating the user, the data retrieval engine sends values for tags the user is authorized to view to the web server, for delivery to the browser. The data retrieval engine tracks which values were sent to the web server for each user and when. When the data retrieval engine receives a request for a specific user, only data not previously provided to the web server for that user is provided for the current request. In this manner, the user does not miss any events, and is provided substantially in real time with a complete set of data for requested tags.