Implementing Domain Driven Design (DDD) with Qlerify
Qlerify DDD Template
DDD is a useful tool for understanding the business domain and designing a software application. Qlerify helps users to quickly identify domain objects through a business user friendly interface and powerful AI features.
It’s easy to create your own DDD model from a template workflow in Qlerify. Qlerify allows you to build, share, and iterate on the template. Get started by signing up for free and create a DEMO project. Then select the DDD template workflow in the DEMO project. See below for more detailed instructions.
What is Domain Driven Design?
Domain-Driven Design (DDD) is a software design approach that focuses on modeling software based on the real-world business domain it is meant to serve.
DDD is particularly valuable in complex domains where the business logic and rules are intricate. It's less beneficial for simple, CRUD (Create, Read, Update, Delete)-type applications where the complexity doesn't warrant the overhead of DDD. As a developer, integrating DDD into your workflow means embracing a mindset of continuous learning and collaboration with domain experts, focusing on the core complexities and business drivers of the application, and adhering to the principles and patterns that DDD provides.
The Primary Goal of DDD is to align the design of software with the underlying business domain it serves. This alignment is key to creating software that is both effective and relevant to business needs.
Why Use DDD?
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Complexity in Large Systems: DDD tackles the challenges posed by complex systems, where traditional software development methods might fail due to the complexity of business rules and processes.
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Business-IT Misalignment: It addresses the disconnect that often occurs between the business's needs and the technical implementation in software development.
Major Benefits of DDD Include
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Improved Communication: It fosters a common language between developers and business stakeholders, ensuring a clearer understanding between business stakeholders and development teams and that software development is closely tied to business requirements.
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Better Software Fit: Software that mirrors business processes and language, resulting in solutions that better fit business needs.
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Clear Architecture: A well-defined structure that helps in organizing code around the business domain.
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Maintainability: The focus on the domain makes it easier to modify and maintain the software as business requirements evolve.
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Scalability: Facilitates the design of scalable systems through bounded contexts and aggregates.
Basic Concepts of DDD
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Ubiquitous Language: A common language used by developers and business stakeholders to ensure clear communication. Each Bounded Context has its own ubiquitous language that is specific and applicable within that context. This language includes terms, concepts, and phrases used by team members and stakeholders.
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Bounded Context: A Bounded Context defines a logical boundary where a specific domain model is defined and applicable. It encapsulates everything inside it - from the code and database schema to the business rules and language (ubiquitous language) used. Example: Consider an e-commerce application with separate parts like "Order Processing", "Inventory Management", and "User Management". Each of these can be a Bounded Context with its own models, rules, and language.
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Domain Objects: Objects that are not just representations of database tables or data structures; they are meaningful constructs that encapsulate the business logic, rules, and behavior of the business domain you are working with. The different types of domain objects include Entities, Value Objects, Aggregates, Domain Events and Services
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Entities: Objects that are identified by their identity, rather than their attributes. For example, two customers with the same name and date of birth are still distinct entities if they have different customer IDs. Entities contain attributes (data) and behaviors (methods) that are relevant to the domain.
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Value Objects: Objects that are defined solely by their attributes and have no conceptual identity and they do not have a unique identifier. For example, an address can contain attributes like street, city, postal code and country. Value Objects are immutable. Once they are created, their state cannot be changed. Any modification results in the creation of a new Value Object.
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Aggregates: A cluster of domain objects (entities and value objects) treated as a single unit for the purpose of data exchanges. Each aggregate has a root entity, known as the aggregate root, which controls access to the other members of the aggregate.
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Repositories: Mechanisms for encapsulating storage, retrieval, and search behavior, acting like a collection of domain objects.
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Domain Events: Significant business events that trigger transactions or other domain actions.
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Services: Business logic that don’t naturally fit within the concept of an Entity or Value Object.
Implementing DDD with Qlerify
It’s easy to create your own DDD model with Qlerify from a template workflow. Qlerify allows you to build, share, and iterate on the template. Get started by signing up for free and then take the following steps to make a DDD model of your own.
1. Initiate the Project with Domain Understanding
Create a DEMO project and select the DDD template workflow in the DEMO project. You can create a clone of the template if you want to keep the original DDD template workflow.
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You can apply a powerful technique called Event Storming to understand the domain and identify the key domain events. This is how it works: Bring together domain experts, business analysts, and development team members and conduct workshops and discussions to deeply understand the business domain, processes, and terminology. Map out the key domain events after a timeline in the workshops. Add desired information such as hotspots, opportunities, systems, roles etc as needed.
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Create a Ubiquitous Language - Develop a common vocabulary that will be used consistently by both technical and non-technical team members. Ensure this language is documented and accessible for reference. Apply this vocabulary when creating models in the Qlerify tool.
2. Identify and Define Bounded Contexts
Identify distinct areas of the business domain that can be treated as separate bounded contexts. Clearly outline the responsibilities and limits of each bounded context. You can do this in the Qlerify tool by selecting different colors for domain events (one color representing a bounded context). Later in the process you can group aggregates into bounded contexts (see below).
3. Model the Domain
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Identify Entities and Value Objects by using the data modeling feature of Qlerify. Select one domain event and click on the tab “Data Models” under the diagram to access the data models view. In DDD, you determine which objects in your domain are entities (having a unique identity) and which are value objects (defined by their attributes). Each attribute can be assigned a read or write tag to illustrate read and write models. Qlerify supports the BEAM methodology (Business Event Analysis and Modeling) to identify data models. Read the following blog post for more information about BEAM.
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Design Aggregates: Qlerify supports visualization of aggregates according to the Software Design level in Event Storming. If you have defined actions (commands) and systems/aggregates for each domain event you can visualize this by clicking on the tab “Aggregates” under the diagram to access the aggregate view. The visualization includes actors/roles, actions (commands), aggregates and domain events as well as the data collection managed by each aggregate. More information here.
4. Generate boilerplate code and unit tests
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Once you have created your DDD model, you can choose to generate boilerplate code for your APIs including code for unit tests. The generated code can be zipped and uploaded to your source code repo.
Please have a look at the help section for more information about how to use the Qlerify tool or reach out for a free demo.
