Obviously they are intended to convey information to designers, manufacturers, builders and so forth, but they can do much more as well. AutoCAD drawings can contain data that can be used by other computer programs to perform a variety of tasks such as creating a bill of materials, validating a design, interfacing to a machine tool or any number of activities. To accomplish this, the AutoCAD drawing must store more than just the graphical data and dimensions. It must also store information that is specific to the interface involved. Sometimes this information will be visible in the drawing, and other times it will not be visible.
Visibility depends on the application and nature of the data.
There are a couple of ways to store information in a drawing that meets these needs. One way is through the use of block attributes. Attributes are independent entities attached to block inserts. They can be used to hold text in a visible or invisible fashion. As a result, they offer a wonderful way for AutoCAD to interface with other applications.