Oracle recently announced Application Integration Architecture (AIA) to
integrate its various applications (11i/R12, Siebel, peoplesoft,
third party application and custom applications). AIA (Application Integration Architecture) will also be used in Fusion Applications.

Key terminology in Application Integration Architecture
Enterprise Business Objects (EBO) – are generic representation of business objects like customer, sales order, invoice, etc… These are entities that describe how business runs.
Enterprise Business Services (EBS) – are specific action that occur
against Enterprise Business Objects(mentioned above). For ex. adding/deleting/modifying an customer, raiseing sales order…You can also think EBS as web service implementation of EBO (Enterprise Business Objects)

How Oracle is targeting to integrate various applications ?
(E-Business Suite, iebel CRM, Peoplesoft, third party application and custom application) answer to this is Application Integration Architecture via Integration Packs
Process Integration Pack - Integration is usually costly, difficult and
prone to break during upgrades. Oracle via Application Integration
Architecture is offering sustainable integration.

Oracle Application Integration Architecture (AIA)- is standard based, open platform designed to make it easier to handle business process across oracle applications (E-Business, Siebel, peoplesoft), third party and custom applications. Using AIA (Application Integration Architecture) Oracle is providing pre-built integration pack for E-Business, Siebel, peoplesoft. These Integrations are based on standard common object model. These standard business objects can be extended by companies based on their specific requirement. Same common business object model is going to be used in Fusion Applications.
Currently oracle offers two components with AIA,
A) Process Industry Packs
B) Industry Reference Models

Oracle has released Siebel CRM ondemand integration pack for E-Business Suite.

Related :
http://www.oracle.com/applications/oracle-application-integration-architecture.html