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Table of contents
1.
Introduction
2.
System Requirements
2.1.
Functional Requirements
2.2.
Non-Functional Requirements
3.
Class Diagram
4.
Use Case Diagram
5.
Code in C++
6.
Data Structures Used
7.
Frequently Asked Questions
7.1.
What is sharding?
7.2.
What is caching?
7.3.
What is CDN?
8.
Conclusion
Last Updated: Mar 27, 2024
Medium

Design Stack Overflow - Low Level Design

Author Suraj Pandey
1 upvote
Master Python: Predicting weather forecasts
Speaker
Ashwin Goyal
Product Manager @

Introduction

Stack Overflow is a question-and-answer platform that allows developers to ask and answer questions about programming concepts, bugs, and issues. It is one of the largest online communities for software developers and is a valuable resource for developers worldwide. In this article, we will discuss the low-level design of the Stack Overflow website.

design stackoverflow

System Requirements

System requirements define the necessary conditions and capabilities a system must meet to fulfill its intended purpose. These requirements are usually classified into two categories: 

  1. Functional Requirements
  2. Non-Functional Requirements

Functional Requirements

Functional requirements describe the specific tasks and function the system must perform to meet its intended purpose. They define the core functionality of the system and what it should be able to do. 

Examples of functional requirements for a website like StackOverflow could include the following:

  • Accounts can be created with a name and type (Guest, Member, Admin, Moderator)
  • Accounts can search and view questions
  • Accounts can ask questions
  • Accounts can earn reputation points
  • Notifications can be sent to an account
  • Badges can be assigned to an account based on reputation
  • Photos can be attached to answers and questions
  • Bounty can be assigned to questions with a reputation value and expiry date
  • Answers can be added to a question with details such as text, account, view count, vote count, flag count, and accept the status.
  • Comments can be added to questions and answers with text, view count, vote count, and flag count.
  • Questions can be created with a title, description, account, view count, vote count, status, closed remarks, answers, comments, tags, photos, and badges.
  • Tags can be added to questions with details such as name, description, daily frequency, and weekly frequency.

Non-Functional Requirements

Non-functional requirements describe the desired qualities and constraints of the system rather than specific tasks and functions. They define how well the system should perform rather than what it should do. 

Examples of non-functional requirements for a website like StackOverflow could include the following:

  • Performance: the website should be fast and responsive, with a minimal amount of time spent loading pages.
  • Security: the website should have robust security measures to protect user data and prevent unauthorized access.
  • Scalability: the website should be able to handle a large number of users and questions without performance degradation.
  • Usability: the website should be user-friendly, with an intuitive interface and easy-to-use features.
  • Availability: the website should be accessible 24/7, with minimal downtime for maintenance and updates.
  • Compatibility: the website should be compatible with multiple devices, such as desktops, laptops, tablets, and smartphones.
  • Interoperability: the website should be able to integrate with other tools and platforms, such as social media and instant messaging apps.
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Class Diagram

A class diagram is a graphical representation of the classes, interfaces, and objects in a system and the relationships between them. A class diagram is a blueprint for creating objects and can be used to visualize and understand the design of a system.

This low-level design of Stack Overflow platform code features a variety of classes that work together to provide a comprehensive experience for users. The main classes include Account, Notification, Badge, Photo, Bounty, Comment, Answer, Tag, and Question.

The Account class allows for four types of accounts - Guest, Member, Admin, and Moderator. Members can ask questions and earn a reputation, while Notifications can be sent to members, and Badges can be assigned to them.

The Question class is central to the platform and includes properties such as title, description, view count, vote count, status, closed remarks, answers, comments, tags, photos, badges, and a bounty.

The Answer class is also crucial, with properties such as text, the Account that posted it, view count, vote count, accepted status, comments, and photos.
In the main function, a Member account is created, and a Notification is sent, along with the assignment of a Badge. The creation of a Question and Answer is also demonstrated, with various properties of the Question and Answer being set.

Class Diagram

Use Case Diagram

A use case diagram is a visual representation of the interactions between the system, actors, and use cases within a software application. It provides a high-level view of the requirements and helps to identify the goals of the system. Use case diagrams are widely used in software development as they help to communicate the functionality of the system to stakeholders in a clear and concise manner.

Use case Diagram

Code in C++

#include <iostream>
#include <vector>
#include <string>

class Account {
public:
  enum AccountType {
    GUEST,
    MEMBER,
    ADMIN,
    MODERATOR
  };

  Account(std::string name, AccountType type) : name_(name), type_(type) {}

  void SearchAndViewQuestions() const {
    std::cout << name_ << " is searching and viewing questions.\n";
  }

  void AskQuestion() const {
    std::cout << name_ << " is asking a question.\n";
  }

  void EarnReputation(int reputation) const {
    std::cout << name_ << " earned " << reputation << " reputation.\n";
  }

  std::string GetName() const {
    return name_;
  }

private:
  std::string name_;
  AccountType type_;
};

class Notification {
public:
  Notification(Account& account) : account_(account) {}

  void SendNotification() const {
    std::cout << "Notification sent to " << account_.GetName() << ".\n";
  }

  void AssignBadge(int reputation) const {
    std::cout << "Badge assigned to " << account_.GetName() << " with " << reputation << " reputation.\n";
  }

private:
  Account& account_;
};

class Badge {
public:
  Badge(std::string name, std::string description)
  : name_(name), description_(description) {}

  std::string name_;
  std::string description_;
};

class Photo {
public:
  Photo(std::string file_name) : file_name_(file_name) {}

  std::string file_name_;
};

class Bounty {
public:
    Bounty(){}
    Bounty(int reputation, std::string expiry_date)
        : reputation_(reputation), expiry_date_(expiry_date) {}

    int reputation_;
    std::string expiry_date_;
};

class Comment {
public:
  Comment(std::string text) : text_(text), view_count_(0), vote_count_(0), flag_count_(0) {}

  std::string text_;
  int view_count_;
  int vote_count_;
  int flag_count_;
};

class Answer {
public:
  Answer(std::string text, Account& account) : text_(text), account_(account), view_count_(0), vote_count_(0), flag_count_(0), accepted_(false) {}

  std::string text_;
  Account& account_;
  int view_count_;
  int vote_count_;
  int flag_count_;
  bool accepted_;
  std::vector<Comment> comments_;
  std::vector<Photo> photos_;
};

class Tag {
public:
    Tag(std::string name, std::string description)
    : name_(name), description_(description), daily_frequency_(0), weekly_frequency_(0) {}

    std::string name_;
    std::string description_;
    int daily_frequency_;
    int weekly_frequency_;
};

class Question {
public:
    Question(std::string title, std::string description, Account& account)
        : title_(title), description_(description), account_(account), view_count_(0), vote_count_(0), status_("open"), closed_remarks_("") {}

    std::string title_;
    std::string description_;
    Account& account_;
    int view_count_;
    int vote_count_;
    std::string status_;
    std::string closed_remarks_;
    std::vector<Answer> answers_;
    std::vector<Comment> comments_;
    std::vector<Tag> tags_;
    std::vector<Photo> photos_;
    std::vector<Badge> badges_;
    Bounty bounty_;
};


int main() {
    Account member("Suraj", Account::MEMBER);
    member.AskQuestion();
    member.EarnReputation(100);

    Notification notification(member);
    notification.SendNotification();
    notification.AssignBadge(200);

    Question question("What is Stack Overflow?", "Can someone explain what #include <iostream>
#include <vector>
#include <string>

class Account {
public:
  enum AccountType {
    GUEST,
    MEMBER,
    ADMIN,
    MODERATOR
  };

  Account(std::string name, AccountType type) : name_(name), type_(type) {}

  void SearchAndViewQuestions() const {
    std::cout << name_ << " is searching and viewing questions.\n";
  }

  void AskQuestion() const {
    std::cout << name_ << " is asking a question.\n";
  }

  void EarnReputation(int reputation) const {
    std::cout << name_ << " earned " << reputation << " reputation.\n";
  }

  std::string GetName() const {
    return name_;
  }

private:
  std::string name_;
  AccountType type_;
};

class Notification {
public:
  Notification(Account& account) : account_(account) {}

  void SendNotification() const {
    std::cout << "Notification sent to " << account_.GetName() << ".\n";
  }

  void AssignBadge(int reputation) const {
    std::cout << "Badge assigned to " << account_.GetName() << " with " << reputation << " reputation.\n";
  }

private:
  Account& account_;
};

class Badge {
public:
  Badge(std::string name, std::string description)
    : name_(name), description_(description) {}

  std::string name_;
  std::string description_;
};

class Photo {
public:
  Photo(std::string file_name) : file_name_(file_name) {}

  std::string file_name_;
};

class Bounty {
public:
    Bounty(){}
    Bounty(int reputation, std::string expiry_date)
        : reputation_(reputation), expiry_date_(expiry_date) {}

    int reputation_;
    std::string expiry_date_;
};

class Comment {
public:
  Comment(std::string text) : text_(text), view_count_(0), vote_count_(0), flag_count_(0) {}

  std::string text_;
  int view_count_;
  int vote_count_;
  int flag_count_;
};

class Answer {
public:
  Answer(std::string text, Account& account) : text_(text), account_(account), view_count_(0), vote_count_(0), flag_count_(0), accepted_(false) {}

  std::string text_;
  Account& account_;
  int view_count_;
  int vote_count_;
  int flag_count_;
  bool accepted_;
  std::vector<Comment> comments_;
  std::vector<Photo> photos_;
};

class Tag {
public:
    Tag(std::string name, std::string description)
    : name_(name), description_(description), daily_frequency_(0), weekly_frequency_(0) {}

    std::string name_;
    std::string description_;
    int daily_frequency_;
    int weekly_frequency_;
};

class Question {
public:
    Question(std::string title, std::string description, Account& account)
        : title_(title), description_(description), account_(account), view_count_(0), vote_count_(0), status_("open"), closed_remarks_("") {}

    std::string title_;
    std::string description_;
    Account& account_;
    int view_count_;
    int vote_count_;
    std::string status_;
    std::string closed_remarks_;
    std::vector<Answer> answers_;
    std::vector<Comment> comments_;
    std::vector<Tag> tags_;
    std::vector<Photo> photos_;
    std::vector<Badge> badges_;
    Bounty bounty_;
};




int main() {
    Account member("Suraj", Account::MEMBER);
    member.AskQuestion();
    member.EarnReputation(100);

    Notification notification(member);
    notification.SendNotification();
    notification.AssignBadge(200);

    Question question("What is Stack Overflow?", "Can someone explain what Stack Overflow is?", member);
    question.view_count_ = 50;
    question.vote_count_ = 20;
    question.status_ = "closed";
    question.closed_remarks_ = "Duplicate";
    question.bounty_ = Bounty(100, "2023-02-01");

    Answer answer1("Stack Overflow is a question and answer site for professional and enthusiast programmers.", member);
    answer1.view_count_ = 30;
    answer1.vote_count_ = 15;
    answer1.accepted_ = true;

    Comment comment1("Great answer!");
    comment1.view_count_ = 10;
    comment1.vote_count_ = 5;
    answer1.comments_.push_back(comment1);

    Photo photo1("stack_overflow_photo.jpg");
    answer1.photos_.push_back(photo1);

    question.answers_.push_back(answer1);

    Tag tag1("programming", "Questions related to programming");
    tag1.daily_frequency_ = 100;
    tag1.weekly_frequency_ = 500;

    Badge badge1("Best Answer", "Awarded to the best answer of a question");

    question.tags_.push_back(tag1);
    question.badges_.push_back(badge1);

    std::cout << "Question Title: " << question.title_ << '\n';
    std::cout << "Question Description: " << question.description_ << '\n';
    std::cout << "Question View Count: " << question.view_count_ << '\n';
    std::cout << "Question Vote Count: " << question.vote_count_ << '\n';
    std::cout << "Question Status: " << question.status_ << '\n';
    std::cout << "Question Closed Remarks: " << question.closed_remarks_ << '\n';
    std::cout << "Question Bounty: " << question.bounty_.reputation_ << " reputation until " << question.bounty_.expiry_date_ << '\n';
    std::cout << "Answer View Count: " << answer1.view_count_ << '\n';
    std::cout << "Answer Vote Count: " << answer1.vote_count_ << '\n';
    std::cout << "Answer Accepted: " << (answer1.accepted_ ? "Yes" : "No") << '\n';
    std::cout << "Comment View Count: " << comment1.view_count_ << '\n';
    std::cout << "Comment Vote Count: " << comment1.vote_count_ << '\n';
    std::cout << "Tag Name: " << tag1.name_ << '\n';
    std::cout << "Tag Description: " << tag1.description_ << '\n';
    std::cout << "Tag Daily Frequency: " << tag1.daily_frequency_ << '\n';
    std::cout << "Tag Weekly Frequency: " << tag1.weekly_frequency_ << '\n';
    std::cout << "Badge Name: " << badge1.name_ << '\n';
    std::cout << "Badge Description: " << badge1.description_ << '\n';

    return 0;
}
 

Output

Suraj is asking a question.
Suraj earned 100 reputation.
Notification sent to Suraj.
Badge assigned to Suraj with 200 reputation.
Question Title: What is Stack Overflow?
Question Description: Can someone explain what Stack Overflow is?
Question View Count: 50
Question Vote Count: 20
Question Status: closed
Question Closed Remarks: Duplicate
Question Bounty: 100 reputation until 2023-02-01
Answer View Count: 30
Answer Vote Count: 15
Answer Accepted: Yes
Comment View Count: 10
Comment Vote Count: 5
Tag Name: programming
Tag Description: Questions related to programming
Tag Daily Frequency: 100
Tag Weekly Frequency: 500
Badge Name: Best Answer
Badge Description: Awarded to the best answer of a question

Data Structures Used

In the code, various data structures are used:

  • enum is used to define named constants (e.g., account types)
  • vector is used to store collections of objects (e.g., comments, photos, tags, badges)
  • string stores sequences of characters (e.g., names, descriptions, text)
  • int stores integers (e.g., view count, vote count, reputation)
  • bool stores boolean values (e.g., accepted)
  • classes define user-defined data types to model entities (e.g., Account, Notification, Badge, etc.).

Frequently Asked Questions

What is sharding?

Sharding is a database partitioning technique where a large database is horizontally split into smaller, more manageable parts called shards. Each shard is a separate instance of the database that contains a subset of the data and is stored on a separate physical server.

What is caching?

Caching is a technique in system design where frequently-used data is temporarily stored in a cache so that it can be quickly retrieved the next time the same data is needed. This can improve the performance and responsiveness of a system by reducing the time it takes to access the data, as the cache can provide the data much faster than a remote data source.

What is CDN?

CDN stands for Content Delivery Network. It is a distributed network of servers that work together to deliver web content to users based on their geographic location. The goal of a CDN is to reduce latency, improve accessibility and increase content available to users.

Conclusion

In conclusion, Stack Overflow is a valuable resource for developers, with a vast community of users that offer help and support for programming-related questions. 

The low-level design of the website involves a complex system of functional and non-functional requirements, including account creation, searching, asking questions, assigning badges, and more. 

The code uses various data structures such as enums, vectors, strings, ints, bools, and classes to store and manipulate data efficiently to achieve these requirements. 

Overall, the design of the Stack Overflow website is well-planned and optimized to provide a seamless user experience to the millions of developers who use it every day.

With this understanding, one can confidently approach complex system design problems in a product-based environment.

You can also consider our System Design Course to give your career an edge over others.

We hope that this article has been of use to you. Please don't hesitate to share your thoughts and feedback in the comments section.

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