Enterprise Application Integration

I have been recently thinking about integration scenarios for different applications and how to take decisions on the way two applications should be integrated.. Infact my question is what are the factors i would consider to make a decision on how two applications will integrate. On the same note as much as there is a benefit that comes out of integration of two applications more often than not there is a resulting consequence based on how the applications integrated

Should the two applications be loosely coupled? This is first one that comes to my mind ,on most occasions the answer is yes it should be loosely coupled, the more loosely coupled the two applications are the more opportunities they have to extend there functionality without affecting each other and the integration itself. If tightly coupled its obvious that the integration breaks when applications change.

Simplicity, if we as developers minimize code involved in the integration of the applications, it becomes easily maintainable and provides better integration.

Integration technology Different integration techniques require varying amounts of specialized software and hardware. These special tools can be expensive, can lead to vendor lock-in, and increase the burden on developers to understand how to use the tools to integrate applications.

Data format , The format in which data is exchanged is important, and it should be borne in mind that the format should be compatible with an independent translator other than the integrating applications itself so that at some point these applications are also able to talk to other applications should there be a need. A related issue is data format evolution and extensibility and how the format can change over time and how that will affect the applications.

Data timeliness , we need to minimize the length of time between when one application decides to share some data and other applications have that data. Data should be exchanged in small chunks, rather than large sets. Latency in data sharing has to be factored into the integration design; the longer, the more opportunity for shared data to become stale, and the more complex integration becomes.

Data or functionality, Integrated applications may also wish to share functionality such that each application can invoke the functionality in the others. But this may have significant consequences for how well the integration works.

Asynchronicity, This is a aspect developers start realising after implementation and performance tests fail, By default we think and code synchronously,  This is especially true of integrated applications, where the remote application may not be running or the network may be unavailable, the source application may wish to simply make shared data available or log a request.