Fred E. Latham
Viggen Corp.
Knoxville, TN

David Siegel
Viggen Corp.
Knoxville, TN

Demin Xiong
Oak Ridge National Laboratory
Oak Ridge, TN
 
Real-time data exchange is a concern of more than a little importance to ITS interoperability. With the rapid advances in computational technology and the technology used for data communications among distributed computational platforms, a computational framework for spatial data interoperability will become essential in ITS applications. Within this framework, real-time data exchange, along with other types of data sharing, process sharing and multiple services access will be possible. To advance such a framework, an interoperability standard will need to be developed from the foundation of a comprehensive ITS data transfer standard; a comprehensive standard that will provide specifications for spatial feature catalogues, spatial objects, attributes and other basic elements.

Many advanced ITS user services require real-time spatial data exchange and communications. Numerous real-time data can be formatted into messages that can be transmitted among distributed ITS application components. Other real-time data, due to their volume, must reside in an on-line database, which will be retrieved upon requested.

Performance, or speed, should not be a criterion of a transfer standard, but when a standard must be used in an environment where performance is critical, it is a factor must be examined carefully. Performance is a concern in this type of transfer standard because a standard is intended to provide flexible and meaningful data transfer. This type of transfer requires complex information engineering, which in return will impact the computational performance or transfer speed. Also a transfer standard is usually used to transfer a complete data set, even when a user needs only part of the data. The user must then extract the necessary data using other programs. Three tactics for addressing the issues are:

Classify those data likely to be transferred in real-time as a special category. When mapping this special category of data into a transfer, a performance measurement can be used to test choices and alternatives. Adopt special options to achieve an efficient design. These options can take advantages of the specifications of the standard, but will be tailored to fulfill the real-time requirements. Develop an independent profile to be compatible with the ITS spatial transfer standard for the purpose of real-time data exchange. This profile will build appropriate formats for the data so as to reduce transfer overhead and allow partial data transfer.

An interoperability standard must be distinguished from a transfer standard, and clarification made as to what a transfer standard can do and can not do with respect to interoperability. A transfer standard must limit the scope of the data to be transferred. By its nature, a transfer standard is designed to transfer large volumes of complete sets of data. In contrast, data exchange in the interoperability framework will take place at all levels of data organization. A transfer standard should focus on the specification of the data. Interoperability however, requires the specification on both the data and the processes that operate on the data. Notably, the process of transferring data through a transfer standard is uni-directional. In the interoperability framework, communication between the data server and the data receiver must be allowed.

Although an interoperability standard and a transfer standard are different, they are highly correlated, especially concerning data representation. It is possible and desirable that the specifications of data models, data structures and data format in a transfer standard will be directly utilized in an interoperability standard. In this respect, the development of a comprehensive ITS data transfer standard should consider the constraints imposed by interoperability requirements; otherwise the transfer standard may become an obstacle rather than a facilitator to spatial data interoperations implementation.