shown in the following diagram, the IBM Cognos architecture is based on a typical three-tiered web architecture that consists of the following components:
a web server
The IBM Cognos web server tier contains one or more IBM Cognos gateways.
applications
The IBM Cognos applications tier contains one or more IBM Cognos servers. An IBM Cognos server runs requests, such as reports, analyses, and queries, that are forwarded by a gateway.
data
The IBM Cognos data tier consists of the content store, data sources, and the metric store.
Figure 1. IBM Cognos server between a Web server and a Data tier