Alexander, best known for his work on patterns, is currently working on a book series called Nature of Order. This book provides a unifying model of design that appeals to naturally occurring processes based on locii called *centers*. He aspires to give buildings, and other built artifacts, the same elegance as one can find in naturally recurring systems. A center is "something we notice" in a system. It is differentiated from neighboring centers by a fuzzy boundary. A hallway is a center; a country pond is a center. Patterns are stereotypical centers. One tenet of the book series is that beauty is objective. That is, given two design choices that build different structures, one is in some sense "better" than the other. This is traditionally held to be a subjective matter. But Alexander maintains that most people will usually choose a given design over its lesser counterpart, and that the choice is experimentally objective. He also notes that these experimental judgments correlate to the presence of about 15 properties such as strong centers, graded variation, local symmetries, etc. Design, then, is the process of intensifying centers. Existing centers can be intensified by adjacent centers. And each center intensifies centers contained within it (for example, an external building facade intensifies each of its windows, perhaps by a graded variation in size with the largest windows on the bottom and the smaller ones on top). The final system is a collection of smoothly integrated centers that reinforce each other. How does one intensify centers or add new centers? As the design unfolds, one must be careful not to destroy the structure of existing centers. Therefore, design is a sequence of structure-preserving transformations. For Alexander, there is only one step in the design "process:" apply a structure-preserving transformation that adds to the wholeness (or "life") of the overall system. Such a transformation usually intensifies existing centers. Alexander has noticed about 15 structure-preserving properties (the number 15 is not exact or special) that are tools for design. These properties are described below. There is one remaining design question: how do you know the order of creating centers, or of visiting centers with the structure-preserving transformations? The order is important. Alexander says that you need to choose the transformation that does the most to preserve the life of the system of a whole, that does the most to preserve wholeness, that has the greatest system-wide impact. For a given kind of system (say, for a Japanese tea house, or a real-time distributed processing system) it is important to follow a process called a *sequence*. A sequence is a tour through the system where each new element is introduced in the context of previously introduced concepts; the dependency between the elements helps establish the order of the sequence. The sequences incorporate immediate feedback, and in that sense are unlike most pre-ordained processes. With a little thought, one can see the mapping of these principles onto many scales of software design; I can see the mapping onto organzational design. There has been some discussion on how to use tools to help designers execute sequences to unfold systems using piecemeal growth instead of using the "big bang" or "kerplop" methods commonly embraced in contemporary design. One thing that strikes me in reading these is the importance of the element of time. We know that in OO systems Simplicity and Inner Calm come in mature systems after several releases and field experience, but to "design it in" up front, with a tool, would be impossible. Therefore, the unfolding process includes the application of the product and must engage the customer. This of course is consistent with Alexander's earlier work, one of the perspectives that motivated his work on patterns. Here are Alexander's 15 structure-preserving properties (from a draft of Nature of Order, Book 2, Part 12). ---------------------- 1. Levels of Scale. For example, within a given center A, or directly near to it, we shall find smaller centers, B, one level of scale smaller. That happens because any perturbation or irregularity which develops near A causes a latent center B. As this latent center gets stronger, this will then cause an aggregation or nucleation near the first center. It _must_ be a jump in scale. If it were too similar in scale (too similar in size), it would not preserve the structure. ... 2. Strong Centers. When structure-preserving transformations are occurring, strong centers will be increasing all the time, quite generally. In the growth of a flower, there is a field effect that takes place, caused by the chemical gradients in the sap. As one center forms--the position of the flower heads--leaves, stems, and other parts of the flower then rearrange themselves to support the flower with sap: and in the process create a field effect which actually intensifies the flower. In general, it must happen in any system where one center forms, as structure-preserving transformations occur, that other smaller centers are then placed, intensified, and themselves strengthened, _in just such a way_ that by virtue of their position and arrangement they intensify the first center. This causes the field effect around the first center which I have described in Strong Centers. Gradually it will occur around every center. 3. Alternating Repetition. Inevitably, in any structure, many events (and structures) repeat. This is typical throughout the world. Atoms, waves, leaves, grains of sand, cirrus clouds, all have the repetition of some given type of center, many times, spread trough a portion of space. ... The effect is quite general. In any repetition, there will, obviously, be latent centers (not-yet-fully-existing centers) in some of the spaces between adjacent centers in the repetition. Assume now, that a structure-preserving transformation occurs. The latent center between some pair of centers will now develop and become a center in its own right. If the spaces between the repeating centers are themselves similar (as they will often be) this center-forming process will gradually occur in all the centers lying between the first system of centers--and this second system will also repeat, between the first set. Within a time, after a number of transformations of this kind, we shall have Alternating Repetition. 4. Boundaries. At any moment in the evolution of a system, each center which exists will have, _latent_, around it, and separating it and joining it to adjacent centers, a boundary zone. This latent boundary zone will, under structure-preserving transformations, intensify and form further centers within the boundary zone, ultimately forming a big boundary which is strong in itself and intensifies the center. ... The process is general. Gradually, under structure-preserving transformations, centers form boundaries, and the property Boundaries will be found repeatedly throughout space. 5. Positive Space. Consider some empty space in a system, currently not inhabited with centers. At least some of this empty space will be latent as a center -- it will be center-like but undeveloped. Sooner or later, a structure-preserving transformation takes this latent center and makes it more center-like. As it becomes a center, it becomes positive. ... And this will happen in general in any system under structure-preserving transformations. Gradually, each bit of space within this empty space that has any latency to be center-like will gradually be formed more and more solidly, as a center. As the empty space is filled, pushed, pulled, connected, each bit of it becomes a center, and thus becomes positive. The property Positive Space appears more and more pervasively throughout the space. 6. Good Shape. Consider an emerging shape with a developing whole. The shape exists, at some early stage, as a shadowy possible shape, not yet very strongly defined. In the course of the structure-preserving transformations, some latent center which appears within this shape or just just next to it, even if only dimly present, will be strengthened and made into a more definite center. ... One by one the vaguely existing centers within the shape are replaced by definite centers. Under the impact of the sp-transformations, the shape strengthens. Gradually, throughout the space, just that character emerges which I have previously defined as Good Shape will appear, each shape is reshaped ;so that it is made throughout, through and through, of centers. 7. Local Symmetries. The centeredness of any given center is almost always strengthened by local symmetry -- not always, but almost always. As electron orbits from around an atom, in the absence of forces making them be asymmetrical, the orbits become symmetrical. The random-seeming aggregation of paths that appears during the evolution of the atom's quantum processes, form local symmetries throughout. In general, during the course of the sp-transformations, as they occur, at least some centers are reinforced and strengthened by Local Symmetries. Each local symmetry intensifies a local center. As structure is preserved, the density of local symmetries will increase, and local symmetries will appear more and more often throughout the space. 8. Deep Interlock and Ambiguity Along any edge between two centers, random perturbations will form disturbances which exist as latent centers. As these randomly occurring latent centers are intensified, they go, one way or another, into one zone or the other zone along the edge. ... As the centers along an edge get strengthened they penetrate more deeply into the two zones (centers) on either side of the edge: thus centers are established which interpenetrate the large centers, causing Deep Interlock or Ambiguity in those cases where the new centers may be read as belonging to either one side or the other. 9. Contrast One necessary result of the structure-preserving process is to give each center its distinctness, more differentiation. In the markings of a zebra, the patterning of the coat comes from growth diffusion mechanisms, under the control of genes. But in evolution, this striping helps to camouflage the zebra in a shaded forest. The closer the marking to the striped pattern of light and dark falling through branches, the better protected the zebra is from predators. The evolution slowly moves the genes to accomplish a striped marking, with greater contrast. To accomplish this, the sp-transformation must increase its contrast. Its differentiation from the surrounding space is gradually intensified, Contrast appears. 10. Graded Variation As any center appears, and the ongoing structure-preserving transformations do what they can to intensify the center, the space around the center will step-by-step form gradients which point towards the center, strengthening it through the field effect. The gradient from warm lower levels in a mountain range, to the higher altitudes, where peak, snow, air, have a different character, all helping to support the centeredness of the mountain peak. Slowly Graded Variation will make its appearance throughout the space, around many of the centers -- at large scales and small. The gradients reinforce and supplement the centers which exist. 11. Roughness As a system comes to order, the structure-preserving pressure to form centers -- especially large centers -- will often refine boundaries, edges, shapes, and connections in somewhat unusual ways. In a system of growing crystals, the crystals take on different shapes and sizes. This is not only because of random fluctuations in the nutrient of the crystal growth. It also happens, as the large configuration emerges, because to maintain the wholeness of the system at large, more material is needed to fill in gaps in one spot; another spot is more crowded. To preserve the wholeness, roughness and variations appear among the centers. To guarantee that the smaller centers really do work to form larger centers, the smaller ones are often made irregular, are syncopated in shape and arrangement, to fit the smaller centers smoothly into larger ones. As a result, slowly, Roughness always makes its appearance. Even in individual atoms, we see roughness -- that is, imperfect similarity -- from one atom to the next within a crystal. Roughness is the necessary apparent irregularity, the outward sign of deeper order as larger centers are perfected. 12 Echoes. While centers are being formed by sp-transformations, it is almost inevitable that from time to time similarities of process appear. In the weatherbeaten face of this old man, the lines and angles all over his face, make a similar pattern, centers are organized with a similar morphology; there are echoes from point to point throughout his face. And in a great many cases these similarities of process then create structural similarities -- Echoes -- in different parts of the system: systems of similar angles and shapes which bear a family resemblance to one another in the different centers where they appear. 13. The Void. As in pruning an orchard, part of the process of structure-preserving requires cleaning out from time to time. Wherever a situation appears where there are too many centers, a cleaning out must occur, to preserve structure, since the conglomeration of centers becomes too confused, and begins to disturb the structure of the centers themselves. We see such a situation even in the sky, the birds flying, the cleaned out air, the void whose vastness makes the small structure of the birds possible, celebrates them, and gives them space for their life. In general, to protect structure, the plethora of smaller, unimportant centers and too richly differentiated space, gets cleaned out -- and replaced by a homogeneous emptiness. Some of the smaller centers are then strengthened by the homogeneous emptiness that appears in the cleaned-out parts. So The Void makes its appearance necessarily, to strengthen smaller centers that are otherwise insignificant. 14. Simplicity and Inner Calm. As the cleaning out of irrelevant structure continues, and centers are further intensified by simplification, slowly a state appears in which nothing ;unnecessary remains present, and in which all irrelevant or confusing centers that irritate the structure or reduce the value of importance of other centers, are removed. The simplification occurs in nature constantly; and even in those man made actions, which are close to nature. For instance, in this field in Tuscany, the cypresses simplify and substantiate the meadow. All simple, and calm. This simplification and simple inner state will come about naturally, as the result of the structure-preserving process. That simple state is described by the property of Inner Calm which thus also makes its appearance as a direct result of sp-transformations. 15. Not-separateness. Throughout, as the structure develops through its uncompleted forms, the pressure to unify, unify continues. Each part becomes wedded more firmly to the others. Exaggerated differences are eliminated. In the ecology of the lake edge we see that the weeds, water, small creatures, bacteria, mud, and reeds all in the shallow water create an unbroken tissue of organisms. In general, as finishing touches, last centers are placed to create a pervasive sheet-like unity. During this process, again structure-preserving, each part becomes inseparable from the others. Not-Separateness appears. As wholeness unfolds, those fifteen structures appear more and more often, and more densely, while latent centers are progressively differentiated and intensified. This is how the fifteen properties appear in nature.