OBA Composition Reference Toolkit

The 2007 Microsoft Office System is a powerful platform for building role based, collaborative, and analytical applications that extend the reach of Line of Business systems and backend applications to information workers across the organization. These Office Business Applications combine the powerful platform capabilities of the Microsoft Office System with the user familiarity of the Office Clients to surface line of business data, information, and processes to information workers directly within the business productivity tools, interfaces, and devices that they use to execute and complete their business tasks......

http://msdn2.microsoft.com/en-us/architecture/cc196391.aspx