The CORA Model

The CORA delivers a reference model for grouping elements on Enterprise level and a detailed description on Software Architecture level. When designing a specific organizational Enterprise Architecture the CORA can be used as a basis for selecting the relevant logical elements and translating them into needed physical elements.

Organizations are moving more and more towards an hybrid IT landscape with different implementations based upon Custom Software Development, Package Based solutions, different technologies and different architecture styles. In order to be able to design a solution within a hybrid landscape we need an architecture model that has no restrictions on implementation type, technology or styles.

We've evaluated five Vendor Software Architectures (Intel, Microsoft, SAP, Oracle and IBM) with respect to layering, elements, and architecture style. The Vendor Software Architectures described are all based on a layered approach to logically grouped elements. Also they have the separation of presentation, business logic and data in common.

However there are differences in the way the layering is drawn down, logical terms and architecture styles amongst others. For a detailed discussion on the vendor architectures and evaluation see the CORA Model book .

In order to be able to model a solution in a hybrid IT landscape we've defined requirements to which the reference architecture shoud comply. The most important general requirements are:

• the reference architecture should be vendor agnostic;
• usage of a layered architecture. A layered architecture is one of the most common techniques to break down complexity. It enables the separation of responsibilities, decoupling, re-usability, portability and substitutability of elements;
• the clustering is around one 'relaxed' layering-scheme. It must be possible to implement different implementation styles;
• easy to understand;
• it should enable the usage of a component model;
• for all layers and elements two aspects always apply: security and IT governance;
• it should be able to be used in describing the Information Systems & Technical Infrastructure at logical and physical level (Enterprise Architecture),  the Software Architecture at enterprise level and  the Software Architecture at project level.

The objective, requirements and principles lead to a layered architecture with six horizontal layers, accompanied by two vertical layers supporting all horizontal layers.

In this article the layers are described shortly. Details are described in upcoming articles.

The Channel Access Layer provides client-specific software to enable access to information systems.

The Presentation Layer provides presentation-specific software for displaying information to the user and handling of user-initiated events.

The Composition Layer provides composition-specific software, clustered in ‘Orchestrated’ and ‘Composed’ elements.

The Integration Layer is the important backbone in this reference architecture. It provides integration-specific software clustered in ‘Synchronous Communication’, ‘A-synchronous Communication’ and ‘Common’ elements.

The Application Layer is the layer where the core business functionality is located.

The Data Layer provides data-specific software clustered in ‘Data Access’ and ‘Data Storage’ elements.

For all horizontal layers the Security aspects are very critical. Security and compliance has an impact on all elements in each of the layers.

IT Governance has impact on all layers and is therefore also a vertical layer.