Typical reasons for integration

• Information Portals
• Data Replication
• Shared Business Functions
• Service-Oriented Architectures
• Distributed Business Processes
• Business-to-Business Integration

Typical Integration Methods

File Transfer
   Pros: no need for special software
   Cons: publisher and consumer must agree on file name convention, directory location, delete strategy, locking mechanism, etc.

Shared Database
   Pros: no semantic dissonance
   Cons: one schema must fit multiple applications

RPC
   Pros: changes to data invoke application directly
   Cons: tightly coupled. machine dependent, inflexible data format, connection must be available real-time, make assumption of platform technology, data format, location and timeliness of service

Trying to portray remote communication as a variant of a local method invocation is
asking for trouble. Such architectures typically result in brittle, hard to maintain and poorly
scalable solutions.

Messaging

  See Systems Integration using Messaging

n-tier
  not integration because different tiers cannot function without each other

Typical methods to access multiple remote services

SOAP/WSDL : calling remote service in a sequential fashion
MQ : sending messages to remote services in a sequential fashion. aggregate results asynchronously
RV : broadcast request for service, remote servers respond if service can be provided

Distributed system and central business management 

One of the key drivers of integration is the fact that a single business transaction is often spread
across many different systems. A previous example showed us that a simple business function
such as “place order” can easily touch six or seven systems. In most cases, all relevant functions
are incorporated inside existing applications. What is missing is the coordination between the
applications. Therefore, we can add a business process management component that manages the
execution of a business function across multiple existing systems.