What is Low Level Design?

Steps involved in the low-level design

The steps involved in low-level design typically include the following:

Understanding requirements

The first step in low-level design is understanding the system's requirements. This includes reviewing the requirements document, talking to stakeholders, and gathering additional information to better understand what the system should do.

Defining the architecture

Once the requirements are understood, the next step is to define the system's architecture. This involves identifying the various components that make up the system and defining how they will interact with each other. 

Designing the components

After defining the architecture, the next step is to design each component in detail. This includes specifying the data structures and algorithms to be used, and defining the interfaces between components.

Defining protocols

In this step, the protocols that will be used for communication between components are defined. This includes specifying the data formats, message structures, and communication protocols that will be used.

Creating UML diagrams

To help communicate the design, UML (Unified Modeling Language) diagrams may be created to illustrate the architecture and the interactions between components.

Reviewing the design

Once the design is completed, it must be reviewed to ensure that it meets the requirements and is technically sound. This may include obtaining feedback from stakeholders and conducting peer reviews. 

Refining the design

If necessary, the design can be refined based on feedback received during the review process. This may involve changing the data structures, algorithms, or protocols used in the design.

Documenting the design

Once the design has been finalized, it is important to document it in a way that is clear, concise, and easy to understand. This may involve creating detailed design specifications or creating diagrams and flowcharts to illustrate the design.

 These are the general steps involved in low-level design. The specific steps and techniques may vary depending on the designed system and the tools and processes used. However, these steps provide a good starting point for anyone involved in low-level design.

Also read, Instruction Format in Computer Architecture

Roadmap to Low Level Design (LLD)

Low-level design (LLD) is a component-level design process that follows a step-by-step refinement process. It involves detailed design and logic of the modules. It's where the actual software components are designed, and it's closer to the actual coding. Here’s a detailed explanation of the pointers in the context of LLD:

Object-Oriented Principles

Object-oriented principles are the cornerstone of modern software design and development. They provide a framework for structuring software programs as collections of encapsulated objects that interact with each other. These principles include encapsulation, which ensures that an object's internal state is hidden from the outside and can only be accessed through well-defined interfaces. Abstraction allows developers to focus on high-level concepts while ignoring specifics. Inheritance creates a hierarchy by allowing a new class to absorb the properties and methods of an existing class, facilitating code reuse and the creation of more complex structures. Polymorphism gives the ability to present the same interface for differing underlying forms, allowing for code that is more flexible and easier to extend.

Process of Analyzing and Design

The process of analyzing and designing in software development involves a systematic approach to understanding problems, defining requirements, and creating a plan for the solution. It starts with requirement analysis, where developers gather and scrutinize the needs and expectations of the end-users. After requirements are understood, the system definition lays out a blueprint of the overall system architecture. Following this, designers create models to represent the system’s components and their relationships, often employing various types of diagrams. Designing the modules then involves specifying the data structures, algorithms, and interface designs for each component in detail. This step-by-step process ensures that the final design is thorough, implementable, and aligned with user needs.

Design Patterns

Design patterns are standardized solutions to common problems in software design. They represent best practices evolved over time and provide a template on how to solve a problem in various situations. Creational patterns, like Singleton and Factory, deal with object creation mechanisms, ensuring that the created objects are suitable for the situation. Structural patterns, like Adapter or Decorator, help design the composition of classes or objects. Behavioral patterns, such as Observer and Strategy, are concerned with communication between objects, making them operate together while maintaining their independence. Employing these patterns can help in achieving a design that is more modular, reusable, and easy to understand.

UML Diagram

Unified Modeling Language (UML) diagrams are a set of graphical notation techniques that provide a standardized way to visualize the design of a system. UML has several types of diagrams, including structure diagrams, such as class diagrams, which illustrate the elements and their static relationships within a system. Behavioral diagrams, like use case diagrams, depict the dynamic behavior of the system and how users interact with it. Interaction diagrams, including sequence diagrams, show how objects interact and the sequence of messages exchanged. UML diagrams are crucial in the LLD process as they help in both the design and communication of complex systems.

SOLID Principles

SOLID principles are a set of five design principles intended to make software designs more understandable, flexible, and maintainable. The Single Responsibility Principle states that a class should have only one reason to change, ensuring that each class addresses a single concern. The Open/Closed Principle suggests that classes should be open for extension but closed for modification, promoting scalability. The Liskov Substitution Principle requires that objects of a superclass should be replaceable with objects of a subclass without affecting the application. The Interface Segregation Principle advises that multiple specific interfaces are better than a single general-purpose interface. Finally, the Dependency Inversion Principle dictates that one should depend upon abstractions, not concretions. These principles guide developers in creating systems that are easier to debug, test, and maintain.

How is LLD different from HLD

 

High-Level Design (HLD)
High-Level Design focuses on the system architecture and the overall framework. It provides a bird's-eye view of the solution, outlining the major components and their interactions with one another. HLD is concerned with the system's broad aspects, such as technology choices, overall system architecture, databases, platform services, and other external dependencies. It addresses how the system will meet the functional requirements of the project, laying out the blueprint for the development process.

In HLD, designers and architects identify the software modules and their high-level functionalities, along with data flow, infrastructure, and communication with third-party services. This phase often results in diagrams and documentation that offer a general understanding of the system, such as a block diagram representing various system components and their interrelationships, typically devoid of intricate details.

Low-Level Design (LLD)
In contrast, Low-Level Design delves into the implementation specifics. LLD is about the internal design of the individual modules identified during the HLD phase. It's akin to zooming in on the components of the HLD to define their precise behavior and structure. LLD includes detailed specifications of the code level, including algorithms, interface designs, procedural details, and complete data models.

LLD's scope encompasses the nitty-gritty details that developers need to follow while coding. It consists of detailed class diagrams with all the methods and attributes, database tables with key constraints, detailed sequence diagrams, and state diagrams. Each element in LLD has enough detail to guide the developer through the coding phase without ambiguity.

Distinction Between HLD and LLD
The primary difference between HLD and LLD is the level of detail and the stage of the software development process at which they are employed. HLD comes earlier and establishes the foundation and the framework within which the application will operate. It defines the macro-level structure, which is crucial for stakeholders to understand the system's core functionality and how it fits within existing systems or infrastructures.

LLD, on the other hand, comes after HLD and is a continuation of the design process, where the general specifications from HLD are translated into concrete, implementable details. LLD is critical for developers as it provides a clear guide for coding and implementation, ensuring that all the system components work together as intended.

In summary, while HLD is more about the 'what' and 'why' of the system components, LLD is focused on the 'how' aspect at a much more detailed and technical level, both HLD and LLD are essential for the successful design and implementation of any software system, each addressing different stages and depths of the design process.

How to form LLD from HLD?

Forming Low-Level Design (LLD) from High-Level Design (HLD) is a process of refining and detailing the conceptual framework provided by HLD into a comprehensive and implementable design. This transformation involves taking the overarching system architecture and component interactions identified in HLD and breaking them down into concrete, detailed specifications that developers can use to write code.

The transition begins with the identification of modules from the HLD and then defining their internal structures. For each module or component, detailed class diagrams are created, specifying the classes, objects, their attributes, and methods along with visibility (public, private, protected). The relationships between classes such as inheritance, association, composition, and aggregation, are also established.

Database designs become more refined in LLD, including exact database schemas, tables, columns, data types, and indices. Detailed sequence diagrams are developed to illustrate the specific sequence of operations that occur within the system for various scenarios, capturing method calls, return statements, and the flow of execution across different system layers.

Interface design is another critical step where the details of external and internal interfaces are specified, including API endpoints, data formats, and protocols. Algorithms are fleshed out in pseudocode or detailed flowcharts, describing the step-by-step logic that needs to be implemented.

Error handling strategies are outlined in LLD, detailing how the system should behave under exceptional circumstances or input errors. Furthermore, detailed state diagrams may be used to depict the different states that the system or its components can be in and the transitions between those states based on events.

In essence, forming LLD from HLD is about taking a step-by-step approach to detail every aspect of the system's components, which includes not only their structure and behavior but also how they integrate and interact with each other and with external entities. This comprehensive detailing serves as the blueprint for the actual coding and implementation phase, ensuring that the high-level design intentions are accurately translated into a functioning software system.

Read more about Software Engineering here.

Benefits of Low-Level Design

Low-level design provides several benefits to the software development process, including:

• Improved Quality: By specifying the detailed design of a system, the low-level design ensures that the system is built to the desired specifications and that the design is well-documented. This can improve the system's overall quality and reduce the chances of bugs and other problems.
   
• Better Understanding: Low-level design provides a detailed understanding of how the system will be implemented, making it easier for developers to understand and implement it correctly. This can reduce the time required for development and improve the overall efficiency of the development process.
   
• Increased Reusability: By defining the interfaces and protocols used for communication between components, low-level design makes it easier to reuse components and systems in the future. This can reduce the cost and time required for future development and improve the overall efficiency of the software development process.

Frequently Asked Questions

What is a low-level design?

Low-level design (LLD) is a detailed blueprint of a software system, outlining classes, functions, and algorithms guiding developers in the implementation phase.

What is LLD vs HLD design?

LLD (Low-Level Design) details individual components and logic for coding, while HLD (High-Level Design) outlines the system's overall architecture and interaction between modules.

What is an example of LLD?

An example of LLD is a detailed class diagram for a shopping cart module, showing attributes, methods, and their interactions for checkout processing.

What are the principles of Low-Level Design?

Low-Level Design (LLD) principles include modularity, encapsulation, abstraction, and separation of concerns. LLD focuses on defining classes, methods, and interactions in detail to ensure maintainability, scalability, and efficient implementation of the system.

Who prepares Low-Level Design document?

The Low-Level Design document is typically prepared by software developers or engineers. They translate the high-level design specifications into detailed, actionable blueprints for coding, focusing on the specific implementation of components and their interactions.

Conclusion

In conclusion, low-level design is an important phase of the software development process that focuses on defining the detailed design of a system. The steps involved in low-level design include understanding the requirements, defining the architecture, designing the components, defining the protocols, creating a UML diagram, reviewing the design, refining the design, and documenting the design.

Low-level design provides many benefits to the software development process, such as better quality, better understandability, and increased reusability, leading to a more efficient and effective software development process.

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