2.1.3 Dimensions of Technical Interoperability
On a digital battlefield, sensors generate bits, communications channels transmit bits, computers process bits, commanders act on information represented as bits, and weapons are directed by messages composed of bits. These bits are the underlying electronic representation of data and information, and to be used they must be interpretable according to some agreed-upon definitions. For two C4I systems to effectively interoperate, they must be able not only to exchange relevant bitstreams but also to interpret the bits they exchange according to consistent definitions--merely providing information in digital form does not necessarily mean that it can be readily shared between C4I systems.
Interoperability also requires that systems are
interoperable at the data level--that the format and semantics of the data are
also coordinated so as to permit interoperation. One significant instance
where this requirement arises is in the exchange of geographical coordinates.
To launch a missile against a target, it is necessary to know the location of
the missile launcher as well as that of the target. The specification of a
location implies the existence of a common coordinate system (and hence a
model of Earth) within which both target and launcher locations can be
specified. Obvious difficulties can arise if the locations of the target and
launcher are specified with respect to different Earth models. If the sensor
and launcher are not using the same Earth model, a transformation of the
sensor-reported location of the target into the launcher's coordinate system
will be necessary. Since it has only been relatively recently that the idea of
using non-co-located sensors for fire control has become practical, the
implicit assumption of identical Earth models for target and launcher may well
not be a valid one. Section
2.3.4 discusses some approaches to the data interoperability challenges.
Thus technical interoperability places detailed demands at multiple levels, which range from physical interconnection to correct interpretation by applications of data that is provided by other applications.