R2R is the use case when content management systems talk directly to each other. The following figure illustrates a typical scenario when content in the enterprise content management system such as Alfresco should be displayed on a website via a web content management system such as Drupal:

A2R is probably the most common use case. You have an application such as a collaboration application, records management application, enterprise CRM system, business process application, web application, portal, design tool, or Office package that wants to work with content in your CMS system. This is now easy with the CMIS interface. The following figure shows a mobile web application, getting its content from an Alfresco repository via CMIS:

A2MR is quite a common use case and handles the case when you want to aggregate content from multiple repositories in an application such as a user interface, or for example a broker application. The following figure illustrates a typical scenario that represents this use case when you have an Enterprise Service Bus (ESB), fetching content from multiple repositories, processing it, and then serving it to an enterprise application:

Another common scenario applicable to this use case is federated search, which is something that is really useful for end users. Instead of going into multiple applications to search for content in a disparate content management system, they can now just go into one search application that is hooked up to all the CMS systems.