Chapter 3. Application Integration pattern 45
Figure 3-2 Direct Connection application pattern
The Direct Connection application pattern has two variations:
? Message Connection variation
? Call Connection variation
All applications of the Direct Connection application pattern will be one variation
or the other. The variation required depends on whether the initiating source
application needs an immediate response from the target application in order to
continue with execution.
Both variations may be used either with synchronous or asynchronous
communication protocols. However, there are preferences for a specific protocol
type depending on the variation. For example, the Call Connection variation has
a more natural fit with synchronous protocols while the Message Connection
variation favors asynchronous protocols.
We examine these two variations in more detail later in this section.
Business and IT drivers
The business and IT drivers for choosing the Direct Connection application
pattern are to:
? Improve the organizational efficiency
? Reduce the latency of business events
? Support a structured exchange within the organization
? Support real-time one-way message flows
? Support real-time request/reply message flows
? Leverage existing skills
? Leverage the legacy investment
Note: The Connection Rules component is not needed when there are no
modeled rules associated with the connection.
Source
Application
Connection
Rules
Target
Application
46 Broker Interactions for Intra- and Inter-enterprise
? Enable back-end application integration
? Minimize application complexity
The primary goal is to allow one application to gain direct and real-time access to
another in order to reduce the latency of business events.
Solution
This Application pattern, as shown in Figure 3-2 on page 45, is divided into a
number of logical components:
? The Source Application tier represents one or more applications that are
interested in initiating an interaction with the target application.
? The Connection is the line between the source application and the target
application representing a point-to-point connection between the two
applications.
? The Connection Rules tier represents any business rules associated with the
connection, such as data mapping rules and security rules.
? The Target Application tier represents a new application, a modified existing
application, or an unmodified existing application. This application is
responsible for implementing the necessary business services.
Guidelines for use
Direct integration between applications can be inflexible, in that any changes to
one application may have knock-on effects on other applications. Changes to the
target application may also require changes to the source application. Such
changes can become both expensive and time consuming, especially when the
target application is being accessed by a number of different source applications.
Different IT departments may also be responsible for developing and maintaining
the source and target applications. Under such a scenario, development might
be difficult to coordinate, especially if the interfaces between the applications
being integrated are not properly defined and documented. Because of this, it is
important to clearly define such interfaces in advance.
Benefits
The Direct Connection application pattern offers the following benefits:
? It works with applications that have simple integration requirements with only
a few back-end applications.
? It increases the organizational efficiency and reduces the latency of business
events by providing real-time access to business data and business logic,
and avoiding manual synchronization of data between applications.
Chapter 3. Application Integration pattern 47
? Direct access to back-end applications reduces the duplication of business
logic across multiple tiers. As a result, changes to business logic can be
made in one tier rather than in multiple applications.
? It can enable re-use of investments already made with the organization.
Limitations
Although this is a reasonable starting Application pattern for integrating
applications in a one to one relationship with one another, this pattern will result
in a many to many “spaghetti” configuration with point to point integration
mappings for each application pair. Also, the expansion of this implementation
into a multi-point configuration will require additional application logic to handle
the coordination.
This pattern cannot be used for intelligent routing of requests, decomposition and
re-composition of requests, and for invoking complex business process workflow
as a result of a request from another application. Under such circumstances, you
should consider a more advanced Application pattern, such as Broker or
Serial/Parallel Process.
Putting the Application pattern to use
ITSO Electronics, an electronics retailer/wholesaler, wants to integrate their retail
and wholesale departments. Currently, both organizations have proven IT
infrastructures but have no interconnectivity. The first process ITSO Electronics
wants to focus on is the inventory and order replenishment process. Currently,
the items sold are tallied at the end of the month by the retail ordering process
and delivered to the wholesale organization by internal mail. This creates a lag in
the inventory replenishment process and causes many out of stock situations. A
primary business goal is to minimize the loss of sales due to out of stock
situations. To meet these requirements ITSO Electronics chooses the Direct
Connection application pattern.
3.4.2 Direct Connection: Message Connection variation
The Message Connection variation, shown in Figure 3-3, applies to solutions
where the business process does not require a response from the target
application within the scope of the interaction.
48 Broker Interactions for Intra- and Inter-enterprise
Figure 3-3 Message Connection variation
Business and IT drivers
The business and IT driver for choosing the Message Connection variation of the
Direct Connection application pattern is to:
? Support real-time one-way message flows
The main driver for selecting this variation is when the business process has no
interest in the result of the operation. This variation also has the most natural fit
when message-oriented middleware is used, such as IBM WebSphere MQ.
Putting the Application pattern to use
In our scenario the retail department of the ITSO Electronics organization needs
to notify the wholesale department to update their inventory records when
a part needs to be ordered. The retail department does not require any
acknowledgement of this request. To meet these requirements, ITSO Electronics
chooses the Message Connection variation of the Direct Connection application
pattern.
3.4.3 Direct Connection: Call Connection variation
The Call Connection variation, shown in Figure 3-4, applies to solutions where
the business process depends on the target application to process a request and
return a response within the scope of the interaction.
Note: We chose not to show the connection rules box in Figure 3-3 because
we want to focus on the connection itself.
Secure Zone
Source
Application
Target
Application
Chapter 3. Application Integration pattern 49
Figure 3-4 Call Connection variation
Business and IT drivers
The business and IT driver for choosing the Call Connection variation of the
Direct Connection application pattern is to:
? Support real-time request/reply message flows
The main driver for selecting this variation is when the business process does
require a result message from the interaction.
Putting the Application pattern to use
In our scenario the retail department of the ITSO Electronics organization needs
to be advised by the wholesale department of the expected delivery date of a
part on order that is out of stock with the retail department. To meet these
requirements, ITSO Electronics chooses the Call Connection variation of the
Direct Connection application pattern.
3.4.4 Broker application pattern
The Broker application pattern, shown in Figure 3-5, is based on a 1-to-N
topology that separates distribution rules from the applications. It allows a single
interaction from the source application to be distributed to multiple target
applications concurrently. This application pattern reduces the proliferation of
point-to-point connections.
Note: We chose not to show the connection rules box in Figure 3-4 because
we want to focus on the connection itself.
Secure Zone
Source
Application
Target
Application
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