Supporting Subdomains are a key concept in Domain-Driven Design (DDD), functioning as specialized segments within a software system that play a significant role in enhancing and supporting the primary business functionalities, yet do not constitute the central focus of the business strategy. While they are more critical and bespoke than generic subdomains (common functionalities like logging or user authentication), supporting subdomains do not carry the core business value, which is reserved for core subdomains (unique and essential business processes specific to the system).
In the ecosystem of a complex application, supporting subdomains are vital in ensuring the overall efficiency and effectiveness of the core domain. They provide necessary functionalities that, although not unique or central to the business model, are tailored to support and streamline the operations of the core domain. For instance, in an e-commerce platform, while the shopping cart feature might be part of the core domain, a product review system could be a supporting subdomain—integral for enhancing user experience but not a primary business driver.
Often, solutions in supporting subdomains can be addressed using standard practices or off-the-shelf software, as opposed to the custom solutions often required in the core domain. This is because innovation in these areas doesn’t usually translate into significant business value. The supporting subdomain’s model is usually simpler than the core domain’s model and focuses on effectively fulfilling its supporting role.
Example
Let’s consider the example of an e-commerce retailer to understand supporting subdomains. In this context, while the core subdomain revolves around the online shopping system – encompassing the product catalog, shopping cart, and checkout process, there are other crucial supporting subdomains that enhance and facilitate these core activities.
- Customer Review System: This system allows customers to post reviews and ratings for products they have purchased. It plays a significant role in influencing other customers’ buying decisions and building trust, even though it doesn’t directly handle sales transactions.
- Recommendation Engine: This is a tool that suggests products to customers based on their browsing and purchase history. It’s instrumental in boosting sales and enriching the customer experience, supporting the core sales process from the sidelines.
- Order Tracking System: After a purchase, customers can track their order’s journey from processing to delivery. This system boosts customer satisfaction and confidence in the platform, complimenting the core processes of transaction and fulfillment.
In an e-commerce setting, these supporting subdomains are indispensable for a complete service offering. They add significant value to the user experience and operational effectiveness, supporting the core domain of online shopping without being the central focus of the business.
Domain-driven Design: A Practitioner's Guide 