Requirements

Imagine you're tasked with building an advertising system for a website, a fundamental component of many online platforms. This isn't just about displaying ads; it's about creating a flexible, maintainable, and efficient system that can adapt to various ad formats, targeting strategies, and evolving business needs. This system needs to handle ad requests, select appropriate ads based on various criteria (user demographics, page content, time of day, etc.), and track ad impressions and clicks. A simple, monolithic approach will quickly become unwieldy as the features and complexity increase. We need a robust object-oriented design to build this system. # Requirements ## Functional Requirements 1. **Ad Creation and Management:** * Support creation of different types of Ads (Text Ads, Image Ads, Video Ads). * Allow associating Ads with Campaigns. * Enable setting a budget (daily, total) for each Campaign. * Implement an approval workflow for new Ads. Admins should be able to approve or reject ads. * Ads should have start and end dates. * Ads should have priorities to control the order they are shown in the absence of other targeting rules. 2. **Targeting:** * Target Ads based on user demographics (age, location, interests). * Target Ads based on website content (keywords, categories). * Target Ads based on time of day. * Implement frequency capping (limit the number of times a user sees a specific Ad). 3. **Ad Serving:** * Retrieve eligible Ads based on targeting criteria. * Select the most appropriate Ad from the eligible pool (e.g., based on priority, remaining budget). * Record Ad impressions (when an Ad is displayed). * Record Ad clicks (when a user clicks on an Ad). 4. **Reporting:** * Generate reports on Ad impressions, clicks, and click-through rates (CTR). * Provide reports aggregated by Ad, Campaign, and date. * Provide real-time or near real-time reporting. 5. **Bidding and Pricing:** * Support different bidding models, such as CPM (Cost Per Mille) and CPC (Cost Per Click). * Handle ad pricing and budget allocation. * Determine the winning ad based on the bidding model. * Integration with billing system (Out of Scope, just logging enough info). 6. **Ad Rendering:** * Provide different Ad Rendering Templates based on the channel or platform. Ex: Mobile App, Desktop Website. ## Non-Functional Requirements 1. **Extensibility:** The system should be easily extensible to support new Ad formats, targeting criteria, and bidding models without requiring significant code changes. 2. **Maintainability:** The codebase should be well-structured and easy to understand, making it easier to maintain and debug. 3. **Testability:** The system should be designed in a way that facilitates unit testing and integration testing. 4. **Concurrency:** The Ad serving component should be able to handle a high volume of requests concurrently without performance degradation. Consider thread safety where relevant. 5. **Modularity:** The system should be composed of loosely coupled modules, each responsible for a specific aspect of the functionality. 6. **Performance:** Ad serving should be fast and efficient, minimizing latency. While specific latency targets are not defined, the design should avoid unnecessary bottlenecks. 7. **Scalability:** The system should be scalable to handle increasing traffic and data volume. Consider how data structures may impact performance at scale, focusing on memory footprint and computational complexity. ## Core Entities 1. **Ad:** Represents an individual advertisement. Attributes include: * `AdId`: Unique identifier. * `AdType`: Type of Ad (Text, Image, Video). * `Content`: The actual content of the Ad (text, image URL, video URL). * `Campaign`: The campaign to which the Ad belongs. * `TargetingCriteria`: Criteria for targeting the Ad (demographics, keywords, etc.). * `StartDate`: Start date for serving the Ad. * `EndDate`: End date for serving the Ad. * `Priority`: Integer representing the priority of the Ad. Higher value means higher priority. * `Status`: Enum (e.g., `PENDING_APPROVAL`, `APPROVED`, `REJECTED`, `ACTIVE`, `INACTIVE`). * `Bid`: Bidding information associated with the ad (price, bidding strategy). 2. **Campaign:** Represents an advertising campaign. Attributes include: * `CampaignId`: Unique identifier. * `Name`: Name of the campaign. * `Budget`: Total budget for the campaign. * `DailyBudget`: Daily budget for the campaign. * `StartDate`: Start date for the campaign. * `EndDate`: End date for the campaign. * `BiddingStrategy`: Defines the bidding strategy for the campaign. 3. **User:** Represents a website user. Attributes include: * `UserId`: Unique identifier. * `Age`: User's age. * `Location`: User's location. * `Interests`: User's interests (list of keywords). 4. **TargetingCriteria:** Encapsulates the targeting rules for an Ad. This could be an interface with implementations for different targeting strategies. * `DemographicsTargeting`: Targeting based on user demographics (age, location). * `ContentTargeting`: Targeting based on website content (keywords). * `TimeOfDayTargeting`: Targeting based on time of day. 5. **AdServer:** The main component responsible for serving Ads. * `getAd(User user, WebsitePage page)`: Returns the most appropriate Ad for the given user and page. 6. **AdRenderer:** Renders the Ad to the appropriate format based on the channel. * `renderAd(Ad ad, Channel channel)`: Returns the rendered Ad for the given channel. 7. **Bid:** Represents the bid information. * `BidType`: Enum (CPC, CPM). * `Amount`: Bid Amount. 8. **Impression:** Represents an ad impression. * `AdId`: The ID of the ad that was displayed. * `UserId`: The ID of the user who saw the ad. * `Timestamp`: The time the ad was displayed. 9. **Click:** Represents an ad click. * `AdId`: The ID of the ad that was clicked. * `UserId`: The ID of the user who clicked the ad. * `Timestamp`: The time the ad was clicked. 10. **Channel:** Represents the platform in which the Ad is being displayed. * `ChannelType`: Enum (MOBILE_APP, DESKTOP_WEBSITE)

Design Ads system for a website.

Requirements

Interview Simulation

Functional Requirements

💡 Interview Tip

Non-Functional Requirements

Core Entity Identification

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