In VHDL each data element is being viewed as a so called object . Each data object of a VHDL program must be declared prior to its use. This value remain constant till the end of the program. Variables can be assigned new values as often as required. Signals are variables, which communicate with an event list in which the so called transactions are being handled.
Files are variable memory sections which are only accessible over special file functions.
Additionally the object must be characterized with a certain data type and an identifier . The data type determines the value set and the allowed operations for that object. The object is then accessible over the Identifier. The diverse data types supported by VHDL will be described in the following chapters where object declarations will be viewed in chapter 3.5.