A data connection is a relationship that specifies the way data are copied between:
A database and a replication process - to replicate data from a database to another.
A data store (database, XML document, business process, and flat file) and a transformation process – to model data inputs and outputs in the modeling of data transformations. For more information about data transformations, see Building Data Transformation Diagrams.
Two data stores with associated models – to show the way data are mapped between models.
The way you draw a data connection determines its direction, and the way objects at its extremities use the data: