 Computer-aided design also known as CAD was originally the type of program that architects used, but since CAD could not offer all the tools that architects needed to complete a project, CAAD developed as a distinct class of software.All CAD and CAAD systems employ a database with geometric and other properties of objects; they all have some kind of graphic user interface to manipulate a visual representation rather than the database; and they are all more or less concerned with assembling designs from standard and non-standard pieces.Currently, the main distinction which causes one to speak of CAAD rather than CAD lies in the domain knowledge (architecture-specific objects, techniques, data, and process support) embedded in the system.