Many Cyber-Physical Systems (CPS), distributed real-time embedded (DRE) applications such as military command and control, time critical planning collaboration systems, and wireless embedded sensor networks require that data shared among various components of such systems must be available within stringent deadlines for timely processing and critical decisions making. In order for these decisions to be correct and in accordance with the current situation, the data received and processed must also be valid. Therefore these applications require a data distribution mechanism that can deliver valid data within specified time frame. This work provides a theoretical base, data models and algorithms necessary for computation of distribution deadlines, which ensure data validity in both static and dynamic cases. A working implementation of data delivery mechanism called Timely Data Distribution Service (TDDS) is also described. This work should be useful to professionals dealing with data in various real-time environments, or anyone else who might be interested in the subject.