A data item describes an atomic state of a particular object concerning a specific property at a certain time point.
Any type of complex information can be broken down to elementary data items (atomic state).
Data items are identified by object (o), property (p) and time (t), while the value (v) is a function of o, p and t: v = F(o,p,t).
Values typically are represented by symbols like numbers, texts, images, sounds or videos.
Often, time is not explicitly expressed and is an attribute applying to the complete data set.