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- ## Example 1 ##
- These are two design approaches, which can be explained as:
- You can imagine a tree like structure , in which when you
- are following top-down appoarch you move from root node to
- leaf node and when you follow bottom-up apprach you follow
- leaf node to root node.
- ### Top-down approach:
- In this an overview of the system is first 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.
- ### Bottom-up approach:
- In this 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.
- ## Example2 ##
- Top down design proceeds from the abstract entity to get to
- the concrete design. Bottom up design proceeds from the
- concrete design to get to the abstract entity.
- Top down design is most often used in designing brand new
- systems, while bottom up design is sometimes used when one
- is reverse engineering a design; i.e. when one is trying to
- figure out what somebody else designed in an existing system.
- Bottom up design begins the design with the lowest level
- modules or subsystems, and progresses upward to the main
- program, module, or subsystem. With bottom up design, a
- structure chart is necessary to determine the order of
- execution, and the development of drivers is necessary to
- complete the bottom up approach.
- Top down design, on the other hand, begins the design with
- the main or top-level module, and progresses downward to the
- lowest level modules or subsystems.
- Real life sometimes is a combination of top down design and
- bottom up design. For instance, data modeling sessions tend
- to be iterative, bouncing back and forth between top down
- and bottom up modes, as the need arises.
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