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PI Web Service Overview

The PI Web Service is a web application that enables developers on virtually any web-aware platform to retrieve data from OSI's PI historian. It acts as a single point of access to PI data and eliminates the need to install any client-side software.

The PI Service allows speedy access to current and archived data and can be configured to permit writing data down to the historian. Multiple queries can run in parallel. The full range of  sample methods can be utilised such as raw, average or standard deviation. It provides a web-based GUI for interactive queries and administration. 

Centralised connection management and diagnostic logging permits a dramatic reduction in support requirements. Connection pooling and caching techniques give rise to marked improvements in developer productivity. As a bonus, there is usually an across-the-board improvement in application performance, sometimes by two orders of magnitude.


The PI Service was written in response to a business requirement for a unified and reliable way to interface to the PI historian. While OSI provides the PI-API and PI-SDK, both of these toolkits require significant programming skills to retrieve data in a robust and efficient way. Furthermore, either the API or the SDK has to be installed on each client machine to allow applications to run, and the firewall must be configured to allow each client direct access the historian.

It is frequently the case that use of the PI-API or PI-SDK can give rise to slow, inefficient and hard-to-manage architectures. Without tight controls and standards, a variety of approaches can  proliferate over time according to the skills and preferences of locally-available developers. The original version of the PI Service was written to replace an uncontrolled ecosystem of several different applications, some of which were leaking resources to the extent that the historian had to be restarted. There was no way of finding out which were the offending applications.