Difference Between Top-down And Bottom-Up Approach In Programming

Top-down and bottom-up approach are both strategies of information processing and knowledge ordering, used in a variety of fields including software, humanistic and scientific theories and management and organization. In practice, they can be seen as a style of thinking, teaching or leadership. In this article get to understand the underlying difference between top-down and bottom up approach in software programming.

Top-down Approach

In programming, a top-down approach, also referred to as stepwise design a complex algorithm is broken down into smaller units, referred to as modules. By breaking down a complex algorithm into smaller units, top-down approach reduces the complications that usually arise while designing algorithms.

In other words, the basic task of a top-down approach is to divide the problem into units and then divide units into smaller sub-units and so on. In this approach, the main module is first developed and then the next level modules are developed. The procedure is continued until all the modules are developed. In this approach, each function in a code is unique and works independently of other functions.

Well, you start at the most abstract level, by defining the problem and from there add more details. It’s a bit like starting within an outline and then filling in as you go until you have a story. Structure/procedure oriented programming languages like COBOL, Fortran and C programming language follows top-down approach.

What You Need To Know About Top-down Approach

1. In Top-down approach, the primary focus is on breaking the larger problem into smaller units and then repeating the process with each problem.
2. Top-down model has high level of redundancy as the size of the project increases.
3. Top-down model is based on decomposition approach.
4. With Top-down approach, it may not be possible to break the problem into set of smaller problems.  
5. Top-down approach is mainly used in code implementation, test case generation, debugging and module documentation.
6. The procedural programming languages such as Fortran, COBOL and C follows a top-down approach.
7. Top-down approach, the modules do not require the modules to have a well-established line of communication among them.
8. In the to-down approach, each module and sub-module are processed separately.

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Bottom-Up Approach

Bottom-up approach entails designing an algorithm by starting at the very basic level and built it up towards the complex level.  In the approach the modules are designed independently and are then integrated together to form a complete algorithmic design.

In this approach, bottom level modules are developed, tested and debugged first, and then the next modules are developed, tested and debugged prior to integrating them to build a concrete solution. The same process is continued until all modules have been completed. Object-oriented programming languages like C++, Java, C#, Perl, Python follows the bottom-up approach.

What You Need To Know About Bottom-Up Approach

1. In bottom-up approach, the primary focus is on identifying and resolving smallest problems and then integrating them together to solve the larger problem.
2. Bottom-up approach has less data redundancy and focus is on re-usability.
3. Bottom-up approach is based on composition approach.
4. In bottom-up approach, it is sometimes quite difficult to identify the general functionality of system in initial stages.
5. Bottom-up approach is mainly used in testing.
6. Object-oriented programming languages like C++, Java, C#, Perl, Python follows the bottom-up approach.
7. In the bottom-up approach, the modules must have a certain degree of interaction and communication among them.
8. Works on the concept of data-hiding and encapsulation.

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Difference Between Top-down And Bottom-Up Approach In Tabular Form

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