Top-down and bottom-up
As top-down ( from top to bottom ) and bottom-up ( from bottom to top ) are two opposite directions of action in processes , which are used in different contexts for analysis or synthesis directions .
To the concept
Top-down goes from the abstract , general, superordinate step-by-step to the concrete, special, subordinate. Bottom-up means the opposite direction. So there are two fundamentally different schools of thought in order to understand, describe and represent complex issues.
Corresponding relationships also exist between the terms:
- Deduction (Latin: deducere = to lead down ; top-down ): an intellectual process from something general (e.g. the concept of humanity ) to something special (a specific individual, e.g. Napoleon)
- Induction ( Latin inductio , "the introduction"; bottom-up ): describes the reverse process
- Decomposition : dismantling, dissolving a whole into individual segments (parts).
- Aggregation : Union of segments (parts) into a whole.
For a better understanding and description (modeling / mapping) of the processes in complex systems such as commercial enterprises, industrial complexes ( chemical plant , nuclear power plant ), social structures, ecosystems , the principles of " top-down and bottom-up modeling" are used. in order to get the most accurate picture possible of reality . Through the mutual application of both principles, one tries to further adapt the image ( model ) to reality.
It should be noted that a model can never completely depict a real complex system, i.e. In other words, there always remains a gradual model uncertainty (see also Probabilistic Safety Analysis , Section Model Uncertainty ).
One of the goals of modeling is therefore to reduce the complexity in the model compared to reality in order to be able to describe it at all (e.g. culture).
The principles of " top-down and bottom-up modeling" are used in particular in methodological applications in hazard and risk analysis , e.g. B. to examine the accident for its - triggering - causes (see below).
When applying the methodology, the principle of Aristotle must always be observed: the whole is greater than the sum of its parts. When a system is broken down into its parts, the material existence of the system is preserved, but its functionality no longer exists (see emergence and holism ).
Areas of application
- In computer science is called a development process for software than top-down , where the design begins with abstract objects, which are then fleshed; the process is bottom-up if it is assumed that individual detailed tasks are required to complete higher-level processes. In addition, in connection with compiler construction of top-down - and bottom-up - parsers spoken.
- Main article: top-down and bottom-up design
- In management theory , top-down means a leadership style that emphasizes the power and authority of the manager (e.g. Frederick Winslow Taylor , Henry Gantt ), while bottom-up sees the manager's role more as motivating the workforce and their skills to use optimally (e.g. Elton Mayo ) (see self-organization in social systems).
- In politics , bottom-up describes the direction of action emanating from party members or from the people of a political movement ; Grassroots movements are typically bottom-up ; Top-down , on the other hand, are campaigns that are centrally controlled and aimed at the individual. Astroturfing is a special case , where a bottom-up movement is only faked.
- In marketing , especially in sales psychology, the dramaturgy of the sales talk as upselling (also top-down selling ) or bottom-up selling , each with opposing, fully equipped initial 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 referred to).
- In cognitive psychology , the terms were adopted from computer science in the late 1940s . In perceptual psychology , the cognitive processing that only happens on the basis of the analysis of the stimulus characteristics (e.g. brightness, color, alignment, etc.) is called bottom-up . Cognitive influences on perception, on the other hand, are referred to as top-down . These influences can be influenced, for example, by prior knowledge of a person or by the meaningful context in which the stimulus information occurs. The top-down process is triggered, among other things, when known stimuli or objects in a suitable context are recognized more quickly.
- In ecology , the processes in ecosystems that are controlled by the population density of the species (the predators ) are understood as top-down . A classic example is the marine kelp forest ecosystem. Here are sea otters , the top predators . They eat sea urchins , which in turn feed on seaweed . If the sea otters disappear from the system, the sea urchins multiply disproportionately and decimate the seaweed. In ecosystems, the bottom-up processes are referred to, which mainly depend on the resources and the primary production (of plants, phytoplankton and benthos or macrophytes) carried out in aquatic ecosystems). If the nutrients in such a system are reduced, the organisms living in it can no longer find enough food (see also: biomanipulation ).
- In nanotechnology , top-down and bottom-up represent basic principles for the production of nanostructures. Top-down refers to manufacturing processes whose origin and method are more closely related to approaches from microsystem technology , such as B. lithography , while bottom-up methods take advantage of the physico-chemical principles of molecular / atomic self-assembly and self-organization , e.g. B. with DNA origami and DNA machines .
- In construction (technology) , 3D models are constructed using 3D CAD according to the bottom-up principle and put together into assemblies (product). The shape of the assembly is therefore dependent on the shape of the individual parts and their installation positions in relation to one another. The future appearance is sketched in the assembly according to the top-down principle. The built-in components reference these sketches. If the assembly sketch changes, the shape of the parts is changed.
- In safety / reliability technology (see also probabilistic safety analysis ), the analytical methods are used according to the top-down principle : fault tree analysis and the bottom-up principle : the event tree analysis , failure type and error effect ( FMEA ) and fault hazard analysis. When analyzes were first used in aerospace and nuclear technology in the 1960s, it had not yet been decided which type of analysis was the most suitable for capturing and evaluating the complex risk structures of the systems. The " Rasmussen study " (WASH-1400, Reactor Safety Study on Assessment of Accident Risk in US Commercial NPP, NUREG-75/014), a holistic approach to Ereignisbaum- and fault tree analysis in 1975 for the first time worked out of both principles Top -down and bottom-up merged. This form has prevailed in all risk analyzes of technical systems to this day .
- In the case of investment , top-down in the economy refers to the analysis “from top to bottom”: Here, the macroeconomics and the industry environment are first considered before individual companies are analyzed. First, a framework plan for the company is created, which is then subdivided, then a review of the feasibility of these partial plans in the lower levels of the company. The corrected plans are then returned, as well as the summary to form an improved master plan. Allegedly, commodities expert Jim Rogers uses this strategy to select his stocks. Bottom-up describes the analysis “from the bottom up”: First, the individual companies are examined in detail before the prospects for entire sectors , markets or regions are considered.
- In the planning is meant by top-down and bottom-up the fact that in urban border and cross-regional planning both the needs of the constantly planning and the contents of the local land-use plans and regional plans are taken into account. To this end, the principle of subsidiarity and the countercurrent principle are applied.
- The Cathedral and the Bazaar ( 1997 essay on software development and open source )
- Linking pin model
- James Hoopes: False Prophets. The Gurus Who Created Modern Management and Why Their Ideas Are Bad for Business Today ( English ). Perseus Publishing, Cambridge MA 2003, ISBN 0-7382-0798-5 : "Top-down and bottom-up in management theory"
- Robert J. Sternberg : Cognitive Psychology. With Contributions of the Investigating Cognitive Psychology Boxes by Jeff Mio. 4th edition, international student edition. Thomson Wadsworth Publishing, Belmont CA et al. 2006, ISBN 0-495-00699-8 , (top-down and bottom-up in cognitive psychology).