Tiers are intrinsically
autonomous entities that are isolated to increase their reusability and efficiency. Business
tiers may share some common functionalities that can be delivered by services. But this overlapping
integration scenario can introduce additional challenges if a service must be aligned
with a number of business tiers and their encompassed domains. This situation is referred to as
multidimensional domain integration, which is further discussed in the following section.
MULTIDIMENSIONAL DOMAIN INTEGRATION STRUCTURES. It is hard to find an organization
that has a lucid definition of a business domain structure. Most configurations combine tiers and
Business Architecture Integration Structures 197
layers to execute business. Smaller organizations, however, may start from a single domain that
organically could develop into a layered structure. As time goes by, more business layers pile up
to form a higher hierarchical composition. As the business evolves, expansion and growth require
the establishment of additional distributed business tiers that reflect different lines of business
generating different sources of revenue.
Vertical and Horizontal Business Structures. A more practical approach would be to combine
domain-layered and tiered-distributed structures. This arrangement enables an organization both to
base its business domains vertically, presented by layers, and to expand its business functionality
horizontally by enabling tiers to be distributed across the enterprise.
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