Software Design Methodology

74 Chapter 4. Software Architecture

4.1 THE NOTION OF ARCHITECTURE

The original meaning of the word architecture, as defined in the Oxford English

Dictionary, is the art or science of building, especially the art or practice of

designing edifices for human use taking both aesthetic and practical factors into

account. It also means a style of building, a mode, manner, or style of construction

or organisations, and structure. Therefore, let’s start the examination of the notion

with buildings.

4.1.1 Architecture in the discipline of buildings

Buildings can be classified according to their main function, or purpose. For

example, houses are for residential accommodation; dovecotes are for housing

doves; lighthouses are coastal towers with lights to warn approaching ships of

dangers, etc. The basic lesson that we can learn from buildings’ architecture is that

the main function of the system is the most important and basic factor and

determines its structure. While the main function of a building largely determines

its structure, other constraints also affect the structural and other features of the

building. For example, each type of building can be further classified by the

structure and its specific usage. Bastel houses are homes in which the residential

quarters are above livestock shelters and storage space. Bungalows are one-storey

houses. Semi-detached houses are two houses joined to form one building.

Terraced houses are a row of connected houses, etc.

While structure in the above sense plays an important role in building, at the

heart of the science and art of architecture are the so-called architectural styles. The

house that my family lives in is not a Georgian house or Victorian house not only

because it is not old enough, but more importantly, because its style is not

Georgian or Victorian. Features of Georgian design include symmetry, simplicity

and classical details such as columns in the classical orders of Doric, Ionic and

Corinthian. The panelled front doors are large, with columns or decorations both

sides and a semi-circular window, known as a fanlight, above. Sash windows,

introduced in the early 18th century, are tall and well proportioned. They have

delicate wooden glazing bars and the panes of glass are all the same size. A typical

example of Georgian houses is the 18th century building the Royal Crescent in

Bath; see Figure 4.1. Victorian houses are those built during the reign of Queen

Victoria from 1837 to 1901. Much of the domestic Victorian housing was modest

and terraced or semi-detached.

Software Design Methodology 75

Figure 4.1 The 18th century crescent of terraced Georgian houses in Bath

The change of architectural styles in history clearly demonstrates the impact

of development of building techniques. When the Normans invaded and conquered

Britain in 1066, they brought the Romanesque style with them. Their skills as

masons and engineers were demonstrated in their massive, solid-constructed

churches and cathedrals. They had perfected the roof-covering technique of

vaulting developed 1000 years earlier by the Romans. This involved the use of

semicircular stone arches extending the length of the roof space to form a barrel

vault. The Norman style has the features that walls are thick, with large smooth-

faced, rectangular dressed stones and an infilling of small stones. Broad buttresses

support the walls. Windows are narrow and semicircular. Doors are surrounded by

semicircular arches, often colourfully decorated with a zigzag and dog-tooth

pattern. Columns are massive circular structures, sometimes covered with

ascending spirals or diamonds and with circular bases sitting on square footings.

Capitals are either square with cushion-type decoration or circular. Norman

architects had encountered difficulties when creating intersections between aisles

of different widths. Their early English successors solved these problems either by

constructing pointed arches because the height of a pointed arch is not determined

by its width, or by raising the level of the springers (the bottom stones) on the

narrower semicircular arch. Churches after the 12th century had lighter, thinner

structures with aisles and naves of varying width. To support the increasingly high

and thin walls, the flying buttress was introduced, which transferred the downward

thrusts to supports away from the main inner wall. This allowed structures to have

larger windows because the walls took less of the overall weight. Because of the

use of pointed arches, the width of doors no longer needed to relate to the height of

the arch. Entrances acquired a more graceful appearance. These are the basic

characteristics of Gothic church architecture. During the 14th century, architects