Encapsulation of an access to some atomic variable. An atomic variable is a variable that cannot be further broken down into lower-level elements and that has one single value. The data item component allows this value to be read and to be set. The data item variable hides the physical nature of the variable (the address at which the variable is stored, the I/O port from which the variable value is read and to which it is written, etc). A component that holds a reference to a data item has a permanent link to the variable encapsulated in the data item. Some data items may give read-only access to a variables. Others may give both read and write access.
See the Connection design pattern.