are strategies of information processing
Information processing is the change of information in any manner detectable by an observer. As such, it is a process which describes everything which happens in the universe, from the falling of a rock to the printing of a text file from a digital computer system...
and knowledge ordering, mostly involving software, but also other humanistic and scientific theories (see systemics
In the context of systems science and systems philosophy, the term systemics refers to an initiative to study systems from a holistic point of view...
). In practice, they can be seen as a style of thinking and teaching. In many cases top–down
is used as a synonym of analysis
Analysis is the process of breaking a complex topic or substance into smaller parts to gain a better understanding of it. The technique has been applied in the study of mathematics and logic since before Aristotle , though analysis as a formal concept is a relatively recent development.The word is...
Decomposition may refer to the following:* Decomposition, biological process through which organic material is reduced* Chemical decomposition or analysis, in chemistry, is the fragmentation of a chemical compound into elements or smaller compounds...
, and bottom–up
approach (also known as step-wise design) is essentially the breaking down of a system to gain insight into its compositional sub-systems. In a top–down approach an overview of the system is formulated, specifying but not detailing any first-level subsystems. Each subsystem is then refined in yet greater detail, sometimes in many additional subsystem levels, until the entire specification is reduced to base elements. A top–down model is often specified with the assistance of "black boxes", these make it easier to manipulate. However, black boxes may fail to elucidate elementary mechanisms or be detailed enough to realistically validate the model.
approach is the piecing together of systems to give rise to grander systems, thus making the original systems sub-systems of the emergent system. Bottom-up processing is a type of information processing
Information processing is the change of information in any manner detectable by an observer. As such, it is a process which describes everything which happens in the universe, from the falling of a rock to the printing of a text file from a digital computer system...
based on incoming data from the environment to form a perception
Perception is the process of attaining awareness or understanding of the environment by organizing and interpreting sensory information. All perception involves signals in the nervous system, which in turn result from physical stimulation of the sense organs...
. Information enters the eyes in one direction (input), and is then turned into an image by the brain that can be interpreted and recognized as a perception (output). In a bottom–up approach the individual base elements of the system are first specified in great detail. These elements are then linked together to form larger subsystems, which then in turn are linked, sometimes in many levels, until a complete top-level system is formed. This strategy often resembles a "seed" model, whereby the beginnings are small but eventually grow in complexity and completeness. However, "organic strategies" may result in a tangle of elements and subsystems, developed in isolation and subject to local optimization as opposed to meeting a global purpose.
- Part of this section is from the Perl Design Patterns Book
Perl Design Patterns Book is an online textbook about Perl style and design and analysis. The contents are licensed under GNU Free Documentation License.-External links:* * in Savannah...
In the software development process
A software development process, also known as a software development life cycle , is a structure imposed on the development of a software product. Similar terms include software life cycle and software process. It is often considered a subset of systems development life cycle...
, the top–down
approaches play a key role.
Top–down approaches emphasize planning and a complete understanding of the system. It is inherent that no coding can begin until a sufficient level of detail has been reached in the design of at least some part of the system. Top–down approach are implemented by attaching the stubs in place of the module. This, however, delays testing of the ultimate functional units of a system until significant design is complete. Bottom–up emphasizes coding and early testing, which can begin as soon as the first module has been specified. This approach, however, runs the risk that modules may be coded without having a clear idea of how they link to other parts of the system, and that such linking may not be as easy as first thought. Re-usability of code is one of the main benefits of the bottom–up approach.
Top–down design was promoted in the 1970s by IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
researcher Harlan Mills
Harlan D. Mills was Professor of Computer Science at the Florida Institute of Technology and founder of Software Engineering Technology, Inc. of Vero Beach, Florida . Mills' contributions to software engineering have had a profound and enduring effect on education and industrial practice. Since...
and Niklaus Wirth
Niklaus Emil Wirth is a Swiss computer scientist, best known for designing several programming languages, including Pascal, and for pioneering several classic topics in software engineering. In 1984 he won the Turing Award for developing a sequence of innovative computer languages.-Biography:Wirth...
. Mills developed structured programming
Structured programming is a programming paradigm aimed on improving the clarity, quality, and development time of a computer program by making extensive use of subroutines, block structures and for and while loops - in contrast to using simple tests and jumps such as the goto statement which could...
concepts for practical use and tested them in a 1969 project to automate the New York Times
The New York Times is an American daily newspaper founded and continuously published in New York City since 1851. The New York Times has won 106 Pulitzer Prizes, the most of any news organization...
morgue index. The engineering and management success of this project led to the spread of the top–down approach through IBM and the rest of the computer industry. Among other achievements, Niklaus Wirth, the developer of Pascal programming language, wrote the influential paper Program Development by Stepwise Refinement
. Since Niklaus Wirth went on to develop languages such as Modula
The Modula programming language is a descendent of the Pascal programming language. It was developed in Switzerland in the late 1970s by Niklaus Wirth, the same person who designed Pascal...
Oberon is a programming language created in 1986 by Professor Niklaus Wirth and his associates at ETH Zurich in Switzerland. It was developed as part of the implementation of the Oberon operating system...
(where one could define a module before knowing about the entire program specification), one can infer that top down programming was not strictly what he promoted. Top–down methods were favored in software engineering
Software Engineering is the application of a systematic, disciplined, quantifiable approach to the development, operation, and maintenance of software, and the study of these approaches; that is, the application of engineering to software...
until the late 1980s, and object-oriented programming
Object-oriented programming is a programming paradigm using "objects" – data structures consisting of data fields and methods together with their interactions – to design applications and computer programs. Programming techniques may include features such as data abstraction,...
assisted in demonstrating the idea that both aspects of top–down and bottom–up programming could be utilized.
Modern software design approaches usually combine both top–down and bottom–up approaches. Although an understanding of the complete system is usually considered necessary for good design, leading theoretically to a top–down approach, most software projects attempt to make use of existing code to some degree. Pre-existing modules give designs a bottom–up flavour. Some design approaches also use an approach where a partially-functional system is designed and coded to completion, and this system is then expanded to fulfill all the requirements for the project
Top–down is a programming style, the mainstay of traditional procedural languages, in which design begins by specifying complex pieces and then dividing them into successively smaller pieces.
The technique for writing a program using top–down methods is to write a main procedure that names all the major functions it will need. Later, the programming team looks at the requirements of each of those functions and the process is repeated. These compartmentalized sub-routines eventually will perform actions so simple they can be easily and concisely coded. When all the various sub-routines have been coded the program is ready for testing.
By defining how the application comes together at a high level, lower level work can be self-contained. By defining how the lower level abstractions are expected to integrate into higher level ones, interfaces become clearly defined.
In a bottom–up approach, the individual base elements of the system are first specified in great detail. These elements are then linked together to form larger subsystems, which then in turn are linked, sometimes in many levels, until a complete top-level system is formed. This strategy often resembles a "seed" model, whereby the beginnings are small, but eventually grow in complexity and completeness.
Object-oriented programing (OOP) is a paradigm that uses "objects" to design applications and computer programs.
In mechanical engineering with software programs such as Pro/ENGINEER, Solidworks, and Autodesk Inventor users can design products as pieces not part of the whole and later add those pieces together to form assemblies like building LEGO. Engineers call this piece part design.
This bottom–up approach has one weakness. Good intuition is necessary to decide the functionality that is to be provided by the module. If a system is to be built from existing system, this approach is more suitable as it starts from some existing modules.
Pro/ENGINEER (as well as other commercial computer-aided design (CAD) programs) does however hold the possibility to create top–down design by the use of so-called skeletons
. They are generic structures that hold information on the overall layout of the product. Parts can inherit interfaces and parameters from this generic structure. Like parts, skeletons can be put into a hierarchy. Thus, it is possible to build the overall layout of a product before the parts are designed.
In computer science and linguistics, parsing, or, more formally, syntactic analysis, is the process of analyzing a text, made of a sequence of tokens , to determine its grammatical structure with respect to a given formal grammar...
is the process of analyzing an input sequence (such as that read from a file or a keyboard) in order to determine its grammatical structure. This method is used in the analysis of both natural language
In the philosophy of language, a natural language is any language which arises in an unpremeditated fashion as the result of the innate facility for language possessed by the human intellect. A natural language is typically used for communication, and may be spoken, signed, or written...
s and computer languages, as in a compiler
A compiler is a computer program that transforms source code written in a programming language into another computer language...
Bottom–up parsing is a strategy for analyzing unknown data relationships that attempts to identify the most fundamental units first, and then to infer higher-order structures from them. Top–down parsers, on the other hand, hypothesize general parse tree
A concrete syntax tree or parse tree or parsing treeis an ordered, rooted tree that represents the syntactic structure of a string according to some formal grammar. In a parse tree, the interior nodes are labeled by non-terminals of the grammar, while the leaf nodes are labeled by terminals of the...
structures and then consider whether the known fundamental structures are compatible with the hypothesis. See Top-down parsing
Top-down parsing is a type of parsing strategy where in one first looks at the highest level of the parse tree and works down the parse tree by using the rewriting rules of a formal grammar...
and Bottom-up parsing
Bottom-up parsing is a strategy for analyzing unknown information that attempts to identify the most fundamental units first, and then to infer higher-order structures from them...
are two approaches for the manufacture of products. These terms were first applied to the field of nanotechnology by the Foresight Institute
The Foresight Institute is a Palo Alto, California-based nonprofit organization for promoting transformative technologies. They sponsor conferences on molecular nanotechnology, publish reports, and produce a newsletter....
in 1989 in order to distinguish between molecular manufacturing (to mass-produce large atomically precise objects) and conventional manufacturing (which can mass-produce large objects that are not atomically precise). Bottom–up approaches seek to have smaller (usually molecular
A molecule is an electrically neutral group of at least two atoms held together by covalent chemical bonds. Molecules are distinguished from ions by their electrical charge...
) components built up into more complex assemblies, while top-down approaches seek to create nanoscale devices by using larger, externally-controlled ones to direct their assembly.
The top-down approach often uses the traditional workshop or microfabrication methods where externally-controlled tools are used to cut, mill, and shape materials into the desired shape and order. Micropatterning
Micropatterning is the art of miniaturisation of patterns. Especially used for electronics, it has recently become a standard in biomaterials engineering and for fundamental research on cellular biology by mean of soft lithography...
techniques, such as photolithography
Photolithography is a process used in microfabrication to selectively remove parts of a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern from a photomask to a light-sensitive chemical "photoresist", or simply "resist," on the substrate...
and inkjet printing belong to this category.
Bottom–up approaches, in contrast, use the chemical
Chemistry is the science of matter, especially its chemical reactions, but also its composition, structure and properties. Chemistry is concerned with atoms and their interactions with other atoms, and particularly with the properties of chemical bonds....
properties of single molecules to cause single-molecule components to (a) self-organize or self-assemble into some useful conformation, or (b) rely on positional assembly. These approaches utilize the concepts of molecular self-assembly
Molecular self-assembly is the process by which molecules adopt a defined arrangement without guidance or management from an outside source. There are two types of self-assembly, intramolecular self-assembly and intermolecular self-assembly...
and/or molecular recognition
The term molecular recognition refers to the specific interaction between two or more molecules through noncovalent bonding such as hydrogen bonding, metal coordination, hydrophobic forces, van der Waals forces, π-π interactions, electrostatic and/or electromagnetic effects...
. See also Supramolecular chemistry
Supramolecular chemistry refers to the area of chemistry beyond the molecules and focuses on the chemical systems made up of a discrete number of assembled molecular subunits or components...
Such bottom–up approaches should, broadly speaking, be able to produce devices in parallel and much cheaper than top-down methods, but could potentially be overwhelmed as the size and complexity of the desired assembly increases.
Neuroscience and psychology
These terms are also employed in neuroscience
Neuroscience is the scientific study of the nervous system. Traditionally, neuroscience has been seen as a branch of biology. However, it is currently an interdisciplinary science that collaborates with other fields such as chemistry, computer science, engineering, linguistics, mathematics,...
, cognitive neuroscience
Cognitive neuroscience is an academic field concerned with the scientific study of biological substrates underlying cognition, with a specific focus on the neural substrates of mental processes. It addresses the questions of how psychological/cognitive functions are produced by the brain...
and cognitive psychology
Cognitive psychology is a subdiscipline of psychology exploring internal mental processes.It is the study of how people perceive, remember, think, speak, and solve problems.Cognitive psychology differs from previous psychological approaches in two key ways....
to discuss the flow of information in processing. Typically sensory
A sensory system is a part of the nervous system responsible for processing sensory information. A sensory system consists of sensory receptors, neural pathways, and parts of the brain involved in sensory perception. Commonly recognized sensory systems are those for vision, hearing, somatic...
input is considered "down", and higher cognitive processes
The executive system is a theorized cognitive system in psychology that controls and manages other cognitive processes. It is responsible for processes that are sometimes referred to as the executive function, executive functions, supervisory attentional system, or cognitive control...
, which have more information from other sources, are considered "up". A bottom–up process is characterized by an absence of higher level direction in sensory processing, whereas a top–down process is characterized by a high level of direction of sensory processing by more cognition, such as goals or targets.
According to Psychology notes written by Dr. Charles Ramskov, a Psychology professor at De Anza College, Rock, Neiser, and Gregory claim that top–down approach involves perception that is an active and constructive process. Additionally, it is an approach not directly given by stimulus input, but is the result of stimulus, internal hypotheses, and expectation interactions. According to Theoretical Synthesis, "when a stimulus is presented short and clarity is uncertain that gives a vague stimulus, perception becomes a top-down approach."
Conversely, Psychology defines bottom–up processing as an approach wherein there is a progression from the individual elements to the whole. According to Ramskov, one proponent of bottom–up approach, Gibson, claims that it is a process that includes visual perception that needs information available from proximal stimulus produced by the distal stimulus. Theoretical Synthesis also claims that bottom–up processing occurs "when a stimulus is presented long and clearly enough."
Cognitively speaking, certain cognitive processes, such as fast reactions or quick visual identification, are considered bottom–up processes because they rely primarily on sensory information, whereas processes such as motor
The motor system is the part of the central nervous system that is involved with movement. It consists of the pyramidal and extrapyramidal system....
control and directed attention are considered top–down because they are goal directed.
Neurologically speaking, some areas of the brain, such as area V1 mostly have bottom–up connections. Other areas, such as the fusiform gyrus
The fusiform gyrus is part of the temporal lobe in Brodmann Area 37. It is also known as the occipitotemporal gyrus. Other sources have the fusiform gyrus above the occipitotemporal gyrus and underneath the parahippocampal gyrus....
have inputs from higher brain areas and are considered to have top–down influence.
The study of visual attention
Attention is the cognitive process of paying attention to one aspect of the environment while ignoring others. Attention is one of the most intensely studied topics within psychology and cognitive neuroscience....
provides an example. If your attention is drawn to a flower in a field, it may be because the color or shape of the flower are visually salient. The information that caused you to attend to the flower came to you in a bottom–up fashion—your attention was not contingent upon knowledge of the flower; the outside stimulus was sufficient on its own.
Contrast this situation with one in which you are looking for a flower. You have a representation of what you are looking for. When you see the object you are looking for, it is salient. This is an example of the use of top–down information.
In cognitive terms, two thinking approaches are distinguished. "Top–down" (or "big chunk") is stereotypically the visionary, or the person who sees the larger picture and overview. Such people focus on the big picture and from that derive the details to support it. "Bottom–up" (or "small chunk") cognition is akin to focusing on the detail primarily, rather than the landscape. The expression "seeing the wood for the trees" references the two styles of cognition.
Management and organization
In management and organizational arenas, the terms "top–down" and "bottom–up" are used to indicate how decisions are made.
A "top–down" approach is one where an executive, decision maker, or other person or body makes a decision. This approach is disseminated under their authority to lower levels in the hierarchy, who are, to a greater or lesser extent, bound by them. For example, a structure in which decisions either are approved by a manager, or approved by his or her authorized representatives based on the manager's prior guidelines, is top–down management.
A "bottom–up" approach is one that works from the grassroots
A grassroots movement is one driven by the politics of a community. The term implies that the creation of the movement and the group supporting it are natural and spontaneous, highlighting the differences between this and a movement that is orchestrated by traditional power structures...
—from a large number of people working together, causing a decision to arise from their joint involvement. A decision by a number of activists, students, or victims of some incident to take action is a "bottom–up" decision.
Positive aspects of top–down approaches include their efficiency and superb overview of higher levels. Also, external effects can be internalized. On the negative side, if reforms are perceived to be imposed ‘from above’, it can be difficult for lower levels to accept them (e.g. Bresser Pereira, Maravall, and Przeworski 1993). Evidence suggests this to be true regardless of the content of reforms (e.g. Dubois 2002). A bottom–up approach allows for more experimentation and a better feeling for what is needed at the bottom.
Both approaches can be found in the organization of states, this involving political decisions.
In bottom–up organized organizations, e.g. ministries and their subordinate entities, decisions are prepared by experts in their fields, which define, out of their expertise, the policy they deem necessary. If they cannot agree, even on a compromise, they escalate
the problem to the next higher hierarchy level, where a decision would be sought. Finally, the highest common principal might have to take the decision. Information is in the debt of the inferior to the superior, which means that the inferior owes information to the superior. In the effect, as soon as inferiors agree, the head of the organization only provides his or her “face″ for the decision which their inferiors have agreed upon.
Among several countries, the German political system provides one of the purest forms of a bottom–up approach. The German Federal Act on the Public Service provides that any inferior has to consult and support any superiors, that he or she – only – has to follow “general guidelines" of the superiors, and that he or she would have to be fully responsible for any own act in office, and would have to follow a specific, formal complaint procedure if in doubt of the legality of an order. Frequently, German politicians had to leave office on the allegation that they took wrong decisions because of their resistance to inferior experts' opinions (this commonly being called to be “beratungsresistent", or resistant to consultation, in German). The historical foundation of this approach lies with the fact that, in the 19th century, many politicians used to be noblemen without appropriate education, who more and more became forced to rely on consultation of educated experts, which (in particular after the Prussian reforms of Stein and Hardenberg) enjoyed the status of financially and personally independent, indismissable, and neutral experts as Beamte
(public servants under public law).
A similar approach can be found in British police laws, where entitlements of police constables are vested in the constable in person and not in the police as an administrative agency, this leading to the single constable being fully responsible for his or her own acts in office, in particular their legality. The experience of two dictatorships in the country and, after the end of such regimes, emerging calls for the legal responsibility of the “aidees of the aidees" (Helfershelfer
) of such regimes also furnished calls for the principle of personal responsibility of any expert for any decision made, this leading to a strengthening of the bottom–up approach, which requires maximum responsibility of the superiors.
In the opposite, the French administration is based on a top–down approach, where regular public servants enjoy no other task than simply to execute decisions made by their superiors. As those superiors also require consultation, this consultation is provided by members of a cabinet
, which is distinctive from the regular ministry staff in terms of staff and organization. Those members who are not members of the cabinet
are not entitled to make any suggestions or to take any decisions of political dimension.
The advantage of the bottom–up approach is the level of expertise provided, combined with the motivating experience of any member of the administration to be responsible and finally the independent “engine" of progress in that field of personal responsibility. A disadvantage is the lack of democratic control and transparency, this leading, from a democratic viewpoint, to the deferment of actual power of policy-making to faceless, if even unknown, public servants. Even the fact that certain politicians might “provide their face" to the actual decisions of their inferiors might not mitigate this effect, but rather strong parliamentary rights of control and influence in legislative procedures (as they do exist in the example of Germany).
The advantage of the top–down principle is that political and administrative responsibilities are clearly distinguished from each other, and that responsibility for political failures can be clearly identified with the relevant office holder. Disadvantages are that the system triggers demotivation of inferiors, who know that their ideas to innovative approaches might not be welcome just because of their position, and that the decision-makers cannot make use of the full range of expertise which their inferiors will have collected.
Administrations in dictatorships
traditionally work according to a strict top–down approach. As civil servants below the level of the political leadership are discouraged from making suggestions, they use to suffer from the lack of expertise which could be provided by the inferiors, which regularly leads to a breakdown of the system after an few decades. Modern communist state
A communist state is a state with a form of government characterized by single-party rule or dominant-party rule of a communist party and a professed allegiance to a Leninist or Marxist-Leninist communist ideology as the guiding principle of the state...
s, which the People's Republic of China
China , officially the People's Republic of China , is the most populous country in the world, with over 1.3 billion citizens. Located in East Asia, the country covers approximately 9.6 million square kilometres...
forms an example of, therefore prefer to define a framework of permissible, or even encouraged, criticism and self-determination by inferiors, which would not affect the major state doctrine, but allows the use of professional and expertise-driven knowledge and the use of it for the decision-making persons in office.
Both top–down and bottom–up approaches exist in public health
Public health is "the science and art of preventing disease, prolonging life and promoting health through the organized efforts and informed choices of society, organizations, public and private, communities and individuals" . It is concerned with threats to health based on population health...
. There are many examples of top–down programs, often run by governments or large inter-governmental organizations (IGOs); many of these are disease-specific or issue-specific, such as HIV
Human immunodeficiency virus is a lentivirus that causes acquired immunodeficiency syndrome , a condition in humans in which progressive failure of the immune system allows life-threatening opportunistic infections and cancers to thrive...
control or Smallpox
Smallpox was an infectious disease unique to humans, caused by either of two virus variants, Variola major and Variola minor. The disease is also known by the Latin names Variola or Variola vera, which is a derivative of the Latin varius, meaning "spotted", or varus, meaning "pimple"...
Eradication is the reduction of an infectious disease's prevalence in the global host population to zero. It is sometimes confused with elimination, which describes either the reduction of an infectious disease's prevalence in a regional population to zero, or the reduction of the global prevalence...
. Examples of bottom–up programs include many small NGOs set up to improve local access to healthcare. However, a lot of programs seek to combine both approaches; for instance, guinea worm eradication, a single-disease international program currently run by the Carter Center
The Carter Center is a nongovernmental, not-for-profit organization founded in 1982 by former U.S. President Jimmy Carter and his wife Rosalynn Carter. In partnership with Emory University, The Carter Center works to advance human rights and alleviate human suffering...
has involved the training of many local volunteers, boosting bottom–up capacity, as have international programs for hygiene, sanitation, and access to primary health-care.
Often, the École des Beaux-Arts
École des Beaux-Arts refers to a number of influential art schools in France. The most famous is the École nationale supérieure des Beaux-Arts, now located on the left bank in Paris, across the Seine from the Louvre, in the 6th arrondissement. The school has a history spanning more than 350 years,...
school of design is said to have primarily promoted top–down design because it taught that an architectural design should begin with a parti
A Parti or Parti pris / from the French Prendre parti meaning " to make a decision ", often referred to as the big idea, is the chief organizing thought or decision behind an architect's design presented in the form of a basic diagram and / or a simple statement....
, a basic plan drawing of the overall project.
By contrast, the Bauhaus
', commonly known simply as Bauhaus, was a school in Germany that combined crafts and the fine arts, and was famous for the approach to design that it publicized and taught. It operated from 1919 to 1933. At that time the German term stood for "School of Building".The Bauhaus school was founded by...
focused on bottom–up design. This method manifested itself in the study of translating small-scale organizational systems to a larger, more architectural scale (as with the woodpanel carving and furniture design).
Ecology is the scientific study of the relations that living organisms have with respect to each other and their natural environment. Variables of interest to ecologists include the composition, distribution, amount , number, and changing states of organisms within and among ecosystems...
, top down control refers to when a top predator controls the structure or population dynamics of the ecosystem
An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....
. The classic example is of kelp forest ecosystems. In such ecosystems, sea otters are a keystone
A keystone species is a species that has a disproportionately large effect on its environment relative to its abundance. Such species play a critical role in maintaining the structure of an ecological community, affecting many other organisms in an ecosystem and helping to determine the types and...
predator. They prey on urchins which in turn eat kelp. When otters are removed, urchin populations grow and reduce the kelp forest creating urchin barrens. In other words, such ecosystems are not controlled by productivity of the kelp but rather a top predator.
Bottom up control in ecosystems refers to ecosystems in which the nutrient supply and productivity and type of primary producers (plants and phytoplankton) control the ecosystem structure. An example would be how plankton populations are controlled by the availability of nutrients. Plankton populations tend to be higher and more complex in areas where upwelling brings nutrients to the surface.
There are many different examples of these concepts. It is not uncommon for populations to be influenced by both types of control.
- "Program Development by Stepwise Refinement", Communications of the ACM, Vol. 14, No. 4, April (1971)
- Integrated Parallel Bottom-up and Top-down Approach. In Proceedings of The International Emergency Management Society’s Fifth Annual Conference (TIEMS 98), May 19–22, Washington DC, USA (1998).
- Changing Your Mind: On the Contributions of Top-Down and Bottom-Up Guidance in Visual Search for Feature Singletons, Journal of Experimental Psychology: Human Perception and Performance, Vol. 29, No. 2, 483–502,2003 Inc.
- K. Eric Drexler and Christine Peterson, Nanotechnology and Enabling Technologies, Foresight Briefing #2, 1989.