The Application Layer
This layer where the core business functionality is located. The layer provides application-specific software clustered into ‘Make’, ‘Buy’ and ‘Legacy’ elements:
• Make. These are Custom Based (bespoke) Solutions (e.g. built with J2EE, .NET).
• Buy. Off the shelf Package Based Solutions (e.g. SAP, Oracle e-business, Microsoft Dynamics).
• Legacy. Existing applications within a landscape (can be both make or buy).


This distinction is necessary when designing an architecture. Aspects such as integration, migration and governance may differ between these clusters. An architecture almost always needs to take into account the legacy of the current IT landscape. The Integration and Composition layer makes it possible to integrate legacy functionality within service oriented solutions.