Streams and tuples

A stream is a sequence of data that flows between operators in a stream application.

A stream can be infinite, such as traffic data. Alternatively, a stream can be finite like the contents of a file. When a streams application contains streams with infinite data, the application runs continuously without ending.

The individual pieces of data within a stream are called tuples which typically represent the state of something at a point in time. For example, a quote from a stock ticker or a reading from a temperature sensor.

A tuple is comprised of a sequence of ordered attributes. An attribute is a named value, and each attribute has a data type. The ordered collection of attribute data types is considered the tuple type.

The following diagram outlines the various components of a stream. The boxes represent tuples lined up in a row. The row of tuples represents a stream. A single tuple is enlarged to show a list of attributes with unique names and values. A list of attribute types is specified outside of the enlarged box. The collection of data types represents the tuple type.

In the example above, one attribute for a tuple has the name "symbol", it is a string type, and its value be "IBM". A second attribute has the name "value", it is a decimal type, and its value is "241.82". The overall tuple can be represented like this "{ symbol="IBM", value=241.82 }". A second tuple on this stream may look like this: "{ symbol="NVDA", value=108.92 }". The tuple type for this example could be represented by tuple<string symbol, decimal value>