are strategies of information processing and knowledge ordering, mostly involving software, but also other humanistic and scientific theories (see systemics). 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 or decomposition, and bottom–up of synthesis.
A bottom–up 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 based on incoming data from the environment to form a perception. 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.Bottom–up approach
Building blocks are an example of bottom–up design because the parts are first created and then assembled without regard to how the parts will work in the assembly.
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.Xem thêm Top-down Approach, Stub và Driver là 2 thuật ngữ thường dùng trong kiểm thử tích hợp.
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