An entity attached to a Subscriber, used to subscribe to a Topic, providing type-safe operations to read/receive data. Each Data Reader can be associated to only one Topic and therefore exactly one data type. This Topic must be created before the Data Reader. A data reader can obtain its subscribed data via two approaches:
There are several ways samples can be read using a data reader, this includes reading with conditions and some buffer management, described in greater detail in your respective language reference guide.
Source: OpenSplice Glossary