Increasingly complex VLSI technology requires configuration and
revision control management. Additionally, it requires efficient
reuse of components when applicable and revision of library components
when necessary.
VHDL uses a library system to maintain designs for modification and
shared use. VHDL refers to a library by an assigned logical name; the
host operating system must translate this logical name into a real
file name and locate it. The current design unit is always compiled
into the Work library; the Work is implicitly available
to the user with no need to declare it. Similarly, the predefined
library STD does not need to be declared before its packages
can be accessed via use clauses. The STD library contains the
VHDL predefined language environment, including the package STANDARD
which contains a set of basic data types and functions and the package
TEXTIO which contains some text handling procedures.
