Enterprise Service Bus (ESB) - Guide to Cloud Computing for Business and Technology Managers - page 194

to integrate additional systems, or to extend the geographical reach of the
ESB infrastructure.
Irrespective of its implementation topology, the main aim of the ESB is to
provide virtualization of the enterprise resources, allowing the business logic
of the enterprise to be developed and managed independently of the infra-
structure, network, and provision of those business services. Implementing
an ESB requires an integrated set of middleware facilities that support the
following interrelated architectural styles:
• Service-oriented architectures (SOAs), where distributed applica-
tions are composed of granular reusable services with well-defined,
published, and standard-compliant interfaces
• Message-driven architectures, where applications send messages
through the ESB to receiving applications
• Event-driven architectures, where applications generate and con-
sume messages independently of one another
The ESB supports these architectural styles and service interaction capabili-
ties and provides the integrated communication, messaging, and event infra-
structure to enable them, as explained in the previous section. To achieve its
stated objectives, the ESB amalgamates functional capabilities of application
servers, integration brokers, and business process management technologies
and product sets into a single integrated infrastructure. These middleware
solutions are discussed in turn in the following sections.
9.2.1 Integration Brokers
To integrate disparate business applications, one must concentrate on the
characteristics and functions of integration brokers, which we covered as
part of the introduction to the distributing infrastructure in Chapter 3,
Section 3.1 “Distributed Applications”.
The integration broker is the system centerpiece. It facilitates information
movement between two or more resources (source and target applications)
and accounts for differences in application semantics and heterogeneous
platforms. The various existing (or component) ESs, such as CRM, ERP
systems, transaction processing monitors, and legacy systems, in this con-
figuration, are connected to the integration broker by means of resource
adapters.
The integration broker architecture presents several advantages given that
integration brokers try to reduce the application integration effort by pro-
viding prebuilt functionality common to many integration scenarios. The
value proposition rests on reuse (in terms of middleware infrastructure and
the application integration logic) across multiple applications and initiatives.
Modern integration brokers incorporate integration functionality such as
transformation facilities, process integration, business process management