Design software traditionally emphasizes what is built and throws out what is not built. Of course what is not built is what we architects call as space. These spaces are what we lovingly put walls (built-matter) around just so that we can live inside those spaces. Unfortunately, we cannot live inside the built-matter (aka walls) unless we are some kind of bugs that burrow into the built-matter. Even when we do product designs, it is the spaces (i.e. holes) that makes the designs useful.
Thirty spokes share the wheel's hub;
It is the center hole that makes it useful.
Shape clay into a vessel,
It is the space within that makes it useful.
Cut doors and windows in a room;
It is the holes which makes it useful.
Therefore profit comes from what is there;
Usefulness from what is not there.
Tao Tse Ching
So TAD Designer Lite (TAD for short) does not talk about built-matter when one starts designing. TAD is concerned about usefulness before profit.
The central concept of TAD is to first arrange the design in terms of the spaces it contains rather than the solid matter. How does the built-matter come into existence? Well, TAD figures it out whenever you need it.
The way TAD figures out the built-matter is quite similar to pouring concrete in the gap between the formwork. Observe the following photograph, and see how the aluminium formwork is in place. Once the formwork is placed as per the plan, concrete is poured in and once that sets, the formwork is removed to reveal the built-matter (In this case, the concrete walls of the house) Now, this is just an example. It is not necessary that every design is made out of concrete. But you get the gist: Just ensure that you put in the boundaries of the spaces, and let TAD figure out where the solid matter will appear.
And how does one put in holes into those walls? Well, when you create that formwork in TAD, you classify the spaces into any one of three types. One of those types is called a connector. It is a special type of space that sits within two or more other spaces. Connectors can be used to determine where the holes are made. Note in the photograph the way the window opening is created in such a manner that concrete when poured does not plug up the opening.
We'll learn more about connectors as we go on. We'll also learn about the other two types of spaces: atoms and envelopes An envelope is that space into which other spaces get in. The outermost silhouette of a building is a envelope. If you want, you can also place solids into your model directly. And there are classifications for solids too. But we are getting ahead of ourselves.
TAD handles both spaces and solids. Both spaces and solids needs to be represented in a design. If we start by placing the spaces; it is possible for the software to work out the solid matter. If we start a design model by placing representations of solid matter, it may not be very easy to work out the spaces. This forces the architect to redundantly represent the spaces -- and that leads to all sorts of errors.
See also this presentation that explains the basic concepts. The presentation made for a workshop in 2002 at Bombay IIT where TAD Designer was being used with heat engines.
Images courtesy of http://picasaweb.google.com/ConcreteForming/ConcreteFormworkSetUpTags: