data streams: semantics

D.Maier, J. Li, P. Tucker, K. Tufte, V. Papadimos, "Semantics of Data Streams and Operators", ICDT 2005, Springer-Verlag 2005

Problem:
1. interpretation of a stream might vary from application to application. Need a mechanism for expressing and reasoning about a stream semantic and representation.
2. needs ways to express the information about content and presentation order.
Solution:
1. Reconstruction Function; maps each prefix, P, of a stream into the desired domain of interpretation
2. stream is viewed as a mixture of finite sub-streams; the ends of a sub-stream can be determined
Questions left:
2. how to determine the end of a sub-stream? What if it's not possible?