Time interval is the most important meta data in Odysseus as it is the base for a semantically correct processing. It is used for applying temporal context to events like in most streaming and event based systems. Without going into deep detail, it allows to map the semantic of streaming operators to the semantic of relational algebra operators and to apply a so called snapshot reducibility.
The time interval is dened defined with a start time stamp and an end time stamp, and describes the temporal validity of the event. Events are only allowed to be processed together if their time intervals overlap (they are valid during the same time). We will give an example below.
You can access the meta data from every stream element with TimeInterval.start and TimeInterval.end (e.g. in MEP or in Select operator)
To set the start time stamp of incoming events, each source in Odysseus must be described (similar to the create table command in SQL), especially a schema giving the attribute names and their data types is needed for tuples. By using the special data type starttimestamp the content of this attribute is interpreted as time stamp and the meta data of the tuple will be set to this application time value. If no information is given, the value is interpreted as milliseconds since 1970, as this is the default case in many systems (e.g., Unix). If no attribute is dened as starttimestamp, the current system time is used as start time stamp.
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