Alternatively, a data-centric methodology provides a much more natural and streamlined way of viewing and modeling many distributed applications. Such a methodology focuses on how the data that is moving and transforming in the system, rather than the processes that are performing those actions.

In other words, the processes encapsulated in the endpoints become secondary. The flow of data defines the essential aspects of the application, and can be modeled with UML class and interaction diagrams. That is not to say that the computational processes are not important, but rather that they are not essential at a high level of design in understanding and mapping out the application. In real-time systems, getting the data to the process that requires it, when it requires it, is essential.

Examples of Data-Centric Applications

There are many real-world applications that are driving the data-centric design evolution. These systems, through necessity of maintainability, flexibility, upgradeability, and affordability, are moving towards a data-centric architecture. The architecture is being realized using COTS middleware and open publish-subscribe data models.

Photo 1 shows a ship in the U.S. Navy designated LPD-17, the first of the San Antonio class of Navy vessels. Real-time messaging middleware underlies a system on this ship class called the Ship- Wide Area Network (SWAN). The SWAN is responsible for shipboard control, machinery control, damage control, integrated condition assessment, steering control, advanced degaussing, mission control systems, navigation systems, and communication systems.

The SWAN is absolutely critical to the ship’s operation and achieving its mission. It comprises hundreds of computers. Because this ship may find itself in the middle of a conflict, it must also be able to take a hit anywhere and continue operations. This required the shipbuilders to look for middleware that supports features like automatic discovery so there would be no configuration. It supports redundant data sources, sinks, data paths, and transports. In fact, you can physically cut the ship network in half and the two halves will work independently. If you reconnect them, they will automatically rediscover and heal the system.

Combat systems are the most demanding real-time systems. Advanced radar systems must handle thousands of simultaneous “tracks” — continuously updated positions of aircraft, ships, vehicles, and missiles in an area. The thousands of radar tracks generate a lot of data, and it must be delivered on time. Many different applications, from display to track managers, need the real-time data. Photo 2 shows an Aegis cruiser launching a missile. The Aegis combat system integrates subsystems like the shipboard navigation system and the radar, weapon system, and tactical displays. A change to any results in costly changes to all. Datacentric approaches are being used to decouple these subsystems, not necessarily improving system effectiveness, but rather making the system easier to build, maintain, and evolve.