Top-down and bottom-up design

As a top -down ( engl. from top to bottom ) and bottom-up ( engl. from bottom to top ) are referred to two opposite directions of action in processes that are used in different contexts of meaning for analysis or synthesis directions. Top-down comes from the abstract, general, superordinate towards gradually to the concrete, particular, subordinates. Bottom-up refers to the opposite direction. ( To describe two fundamentally different ways of thinking to understand complex issues, to represent. )

Such relationships also exist between the terms:

• Deduction (Latin: deducere = down lead, top-down ): a mental process of something universal (eg term humanity ) something special ( a specific individual, such as Napoleon )
• Induction (Latin inductio, " the lead-in ", bottom-up ): refers to the reverse process

As well as

• Aggregation: association of segments ( parts ) into a whole
• Decomposition: Decomposition, resolution of a whole into individual segments ( parts).

Methodology

For a better understanding and description (modeling / mapping ) of the processes in complex systems, such as business corporations, industrial complexes ( chemical plant, nuclear power plant ), social structures, ecosystems, one uses the principles of the " top-down and bottom-up - Modelling", to obtain an accurate image possible from reality. Through the reciprocal application of both principles is trying to further customize the image ( model) of reality.

It should be noted that a model a real complex system can never replicate completely, that is, there always remains a gradual model uncertainty ( see also Probabilistic Safety Analysis, Section model uncertainty).

A goal of the modeling is therefore also reducing the complexity in the model compared to reality in order to describe them at all can ( eg culture).

The principles of the " top-down and bottom-up - Modelling" find particular methodological applications in hazard and risk analysis, eg to prevent accidents on their - to investigate causes of back (see below) - triggering.

In applying the methodology is always the sentence of Aristotle noted: The whole is more than the sum of its parts. With the decomposition of a system into its parts of the material existence of the system is maintained in its functionality exists but not more (see emergence and holism ).

Applications

• In computer science, refers to a process of developing software as a top -down, where the design begins with abstract objects, which are then put into practice; the process is a bottom-up, when it is assumed that each detail functions that are necessary for execution of parent processes. In addition, in the context of compiler construction from top-down and bottom-up parsers is spoken (for more information see top-down and bottom-up design).
• In management theory top-down means a management style that emphasizes the power and authority of the manager (eg, Frederick Winslow Taylor, Henry Gantt ), while bottom-up the role of manager looks more to motivate the workers and their skills optimal use (eg Elton Mayo ) (see self-organization in social systems ).
• In politics Bottom -up refers to the hazards arising from the People's Party or by the people of a political movement direction of action; Grassroots movements typically work bottom-up; Top-down, however, are campaigns that are centrally controlled and directed to the individual. A special case is the so-called Astroturfing, where a bottom-up movement is faked.
• In marketing, especially the psychology of selling the dramaturgy of the sales pitch as a upsell ( and top-down -selling) or bottom-up -selling, each equipped with completely opposite top offers.
• In anthropology and sociology processes of self- organization in social systems as a bottom -up or agency ( agency ) or top-down or structure ( structure ) are called.
• In cognitive psychology, the terms adopted by the computer science in the late 1940s. In the psychology of perception is the cognitive processing (eg, brightness, color, orientation, etc. ) is done only on the basis of the analysis of stimulus features, referred to as bottom-up. Cognitive influences on the perception other hand, are referred to as top-down. These influences can be influenced for example by prior knowledge of a person or by the meaningless containing context in which the stimulus information occurs. The top-down process is triggered, among other things, if known stimuli or objects are detected faster in the appropriate context.
• In ecology, the ecosystem processes that are controlled by the population density of the species ( the predator ), understood as top-down. A classic example is the marine kelp forest ecosystem. Here are the top predators sea otters. They eat sea urchins, which in turn feed on kelp. Disappearance of the sea otters from the system, so the sea urchins proliferate disproportionately and decimate the Tang In ecosystems, the processes bottom-up are known mainly from the resources and usually resulting primary production ( plants, phytoplankton and benthos or macrophytes carried out in aquatic ecosystems ) are controlled. Are the nutrients reduced in such a system, so no longer find the organisms living in enough food (see also: biomanipulation ).
• In the nanotechnology provide top-down and bottom-up principles for the creation of nanostructures dar. Top-down fabrication methods are called, the origin and methodology rather the approaches of microsystems technology, such as lithography match, while bottom-up methods exploit the physicochemical principles of molecular / atomic self-assembly and self-organization, eg in DNA origami and DNA machines.
• In the design ( technology ) can be constructed using 3D CAD using a bottom - up approach, 3D models and compiled into assemblies (product). The shape of the assembly is thus dependent on the shape of the individual parts and their installation positions to each other. After the top-down principle, the future appearance is outlined in the assembly. The internal components are referenced to these sketches. Changes of the assembly sketch, thus the shape of the parts is changed.
• In the Security / Reliability Engineering (see also Probabilistic Safety Analysis ) are the analytical methods based on the principle top-down: fault tree analysis and the principle Bottom -up: The event tree analysis, failure mode and fault effect (FMEA ) and Fault Hazard Analysis are used. In the first applications of the analysis in the aerospace and nuclear technology in the 1960s was not yet decided which type of analysis was the most appropriate in order to capture and evaluate the complex risk structures of the systems. With the " Rasmussen Study" (WASH-1400, Reactor Safety Study on Assessment of Accident Risk in U.S. Commercial NPP, NUREG -75/014 ) a holistic approach for event tree and fault tree analysis was developed in 1975 for the first time, the two principles Top down and bottom -up brought together. This form has prevailed until now in all risk analyzes of technical systems.

Importance in the economy

When investment Bottom -up refers to the analysis " from the bottom up ": Only the individual companies are examined in detail before the prospects of entire industries, markets or regions are considered.

Top -down refers to the analysis of " top down ": First, the macro-economy and the industry environment are considered before individual companies are analyzed. Supposedly, the commodities expert Jim Rogers chooses his shares by the top-down strategy.

First, a framework plan for the company is created, which is then divided, then check for viability of these partial plans in the lower levels of the company. Then the return of the corrected plans and the summary is done in an improved framework.

Importance in spatial planning

In spatial planning is meant by top-down and bottom-up the fact that to be considered in urban -border and cross-regional planning is always both the needs of spatial planning as well as the contents of the local Bauleitpäne and regional plans. For this purpose, the principle of subsidiarity and the countercurrent principle be applied.