BOX 2.5 Interface Standards and Rapid Exploitation of Technology
Information technology is characterized by rapid change. How can such change be exploited by the system designer?
One approach to technology exploitation is to rely on standardized interfaces so as to avoid the need for tight "vertical" integration of system components. Consider, for example, a system consisting of a set of sensors providing input to a set of databases, on top of which is built a system providing data integration, analysis, and decision support. Progress will be made in both the front-end sensor technologies and in the (mostly commercial-off-the-shelf) technologies supporting the back-end analysis and decision support, but this progress may be made at very different rates. Particularly in time-critical applications, it may be the case that frequent upgrades to specific functional capabilities in decision support could pay huge dividends. When care is taken to establish a well-defined interface between the sensors and the databases, and another interface between the databases and the decision support tools, different parts of a system can develop at different rates independently of each other.
It is true that designs that rely on standardized interfaces cannot take advantage of special characteristics of the components themselves, with the result that an interface-based design may have poorer performance in some dimensions (e.g., speed, bandwidth) than a tightly integrated one. Tight integration historically has characterized military systems. For example, in the Joint Tactical Information Distribution System the message formats, the waveforms, and the hardware are highly intertwined. But in addition to not allowing exploitation of all of the good properties of layering (e.g., minimal interaction between layers and thus greater ease in "debugging"), such an approach ignores the fact that a tightly integrated design must--by assumption--proceed at the slowest development pace that characterizes any of its components. In a world in which the underlying technologies evolve so rapidly, the performance benefits of tight integration come at the cost of not being able to use new technology as it becomes available--on balance, a losing proposition.
Well-defined interfaces also enable the creation of reasonably accurate system models for use in optimizing a system and understanding the performance enhancements that will result from specific localized upgrades.