Both of these are types of design approaches that define various parts of a given system, and they follow a different modus operandi. Let us know more about each of them individually before we dive into the difference between top-down and bottom-up approach.
What is a Bottom-Up Model?
It is a design approach that defines the various parts of a system in detail. In this method, after designing and developing the system parts, we link them together for ultimately preparing a bigger component. The process keeps repeating this approach until it finally builds the complete system. The primary advantage of the Bottom-Up Model is that we can make decisions at a very low level. We also get to decide which components we will reuse.
What is a Top-Down Model?
It is basically a system design approach that starts the design from any given system as a whole. In this model, we divide the complete system into various smaller applications containing more details. After this, every part goes through a top-down approach. This process gets repeated time and again until we complete designing the complete system (along with all of its minute details). The Top-Down approach aims at breaking down a bigger problem into smaller individual problems. This way, we can solve them separately (in a recursive manner) and finally deal with the overall system.
Difference Between Bottom-Up Model and Top-Down Model
| Parameters |
Bottom-Up Model |
Top-Down Model |
| Focus |
In this model, we focus on first identifying and then resolving the smallest of the issues. After that, we integrate them into a solution to a bigger problem. |
In this model, we basically focus on breaking down a bigger problem into various smaller ones. This way, we can solve individual smaller issues. |
| Approach |
This model follows the composition approach. |
This model follows the decomposition approach. |
| Languages |
Mostly, various programming languages like C++, Java, etc., that are object-oriented make use of the Bottom-Up Model. |
Various structural programming languages follow the Top-Down Model, such as Fortran, C, etc. |
| Interaction |
This type of model possesses higher interactivity among all of its modules. |
This type of model has issues with tight coupling. Thus, the interactivity among all of the modules involved is pretty low. |
| Redundancy |
This model works better in such cases. It is because it ensures minimum redundancy of data. It has a primary focus on reusability. |
This model shows a higher redundancy ratio with the increase of the given project size. |
| Issues |
In this type of model, it sometimes becomes very difficult to identify the overall functionality of any system in its initial stages. |
In this type of model, the process of breaking down a problem into various sets of minute problems may not be possible at times. |
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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
- In Top-down approach, the primary focus is on breaking the larger problem into smaller units and then repeating the process with each problem.
- Top-down model has high level of redundancy as the size of the project increases.
- Top-down model is based on decomposition approach.
- With Top-down approach, it may not be possible to break the problem into set of smaller problems.
- Top-down approach is mainly used in code implementation, test case generation, debugging and module documentation.
- The procedural programming languages such as Fortran, COBOL and C follows a top-down approach.
- Top-down approach, the modules do not require the modules to have a well-established line of communication among them.
- 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
- In bottom-up approach, the primary focus is on
identifying and resolving smallest problems and then integrating them together
to solve the larger problem.
- Bottom-up approach has less data redundancy and
focus is on re-usability.
- Bottom-up approach is based on composition
approach.
- In bottom-up approach, it is sometimes quite
difficult to identify the general functionality of system in initial stages.
- Bottom-up approach is mainly used in testing.
- Object-oriented programming languages like C++,
Java, C#, Perl, Python follows the bottom-up approach.
- In the bottom-up approach, the modules must have
a certain degree of interaction and communication among them.
- Works on the concept of data-hiding and encapsulation.
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| BASIS OF COMPARISON | TOP-DOWN | BOTTOM-UP APPROACH |
| Description | In Top-down approach, the primary focus is on breaking the larger problem into smaller units and then repeating the process with each problem. | In bottom-up approach, the primary focus is on identifying and resolving smallest problems and then integrating them together to solve the larger problem. |
| Redundancy | It has high level of redundancy as the size of the project increases. | It has less data redundancy and focus is on re-usability. |
| Basis | It is based on decomposition approach. | It is based on composition approach. |
| Disadvantage | It may not be possible to break the problem into set of smaller problems. | It is sometimes quite difficult to identify the general functionality of system in initial stages. |
| Use | It is mainly used in code implementation, test case generation, debugging and module documentation. | It is mainly used in testing. |
| Application | The procedural programming languages such as Fortran, COBOL and C follows a top-down approach. | Object-oriented programming languages like C++, Java, C#, Perl, Python follows the bottom-up approach. |
| Modules | The modules do not require the modules to have a well-established line of communication among them. | The modules must have a certain degree of interaction and communication among them. |
| Work Concept | Each module and sub-module are processed separately. | Works on the concept of data-hiding and encapsulation. |
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