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The Architecting Magic Behind Taking Mash Ups Offline  : Page 2

While most of the complexity you encounter in synchronization efforts will be unique to your application and infrastructure, synchronization works best when it's designed to be a core feature in each data store.

Criteria for Synchronization Architecture
Along with its inherent complexities, synchronization further complicates enterprise data management with problems such as scalability among other areas that can often be partially ignored in a connected application. These areas include:
  • Security
  • Robustness
  • Data transfer volume
  • Application maintainability
It is against these criteria that you will be able to evaluate the synchronization architectures discussed later.

Security. When enterprise data is involved, security is always a concern. Often, in the online case, no data is stored persistently on the device. However, to allow offline access, the data must be stored on the device. Additionally, it is likely that the device is itself mobile (smart phone, laptop, and so on) and can be easily lost or stolen. The offline data must be protected through passwords and encryption from would-be data thieves.

Similarly, the data may need to be synchronized to the enterprise data center over public communication channels such as the cellular phone networks or public Internet access points. This synchronization requires that communications be encrypted and protected from network snoopers.

Robustness. Mobile data also elevates the concern surrounding the robustness of the data. Validity of enterprise data is crucial for decision making. A synchronization operation must leave the data in a consistent state. Although network reliability has improved, your synchronization strategy must gracefully and, above all, consistently handle data and network errors at every stage of the synchronization. In most cases, a half-synchronization of your data is far worse than if the synchronization had never occurred. This problem becomes worse when the synchronization must be done to multiple data sources, including some that are external to your company.

Data transfer volume. For both security concerns and to reduce data transfer costs, the offline application should keep to a minimum its network interactions during synchronization. The application should try to send and receive data that has only changed since the last synchronization. The offline application can be designed to support simple change tracking. Unfortunately, this tracking will not be so simple with large, back-end systems that were only designed for central access.

Because of the limited space available on mobile devices, it is unreasonable to expect that all the enterprise data will be available offline. Unfortunately, many large enterprises' systems that were only designed to be centrally accessed will require that any data filtering or partitioning must be done by the application. This requirement is fine for online applications, but it makes for very large data transfers in the offline case.

Application maintainability. Most online applications can be hosted as web applications and delivered from a single source. As a proof point, most enterprise mash-up tools are web based, which makes maintenance easy because updating the application for all users requires making a change in only one place. In the offline case, just as the data has to be available offline, so too does the application. Creating installed applications introduces all the problems of application versioning and distribution that would have been ignored previously.

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