The purpose of DDD to divide domains, sub domains, core domains, and support domains

A term is used to explain

stay 《DDD The reasons for the rise and the relationship with micro Services 》 There was an example of studying peach trees , If you want to study peach trees , Divide the peach tree into roots according to its organs 、 stem 、 leaf 、 flowers 、 Fruit 、 seeds , Each of these organs can be regarded as a research field , And there are more specific subdivisions in the field , Divided into subdomains 、 Core domain 、 Common domain 、 Support domain, etc , Let's review the peach tree example

Look at the picture above , If studying peach trees is our business , So how to study peach trees more quickly and effectively ？ According to memories , This is how junior high school textbooks are studied :

First step : Identify the subjects of the study , That is, the research field , Here is a peach tree .

The second step : According to some dimensions of the research object , To further split it , Like splitting into organs , And organs can be divided into vegetative organs , reproduction organs , The vegetative organs include roots 、 stem 、 leaf , The reproductive organs include flowers 、 Fruit 、 seeds , So these are the subdomains we want to study .

The third step : Now we can divide the most sub domains , Find the core domain , Common domain , Support domain , As for why it's so divided , I'll explain later , When we find the core domain , And then each sub domain is further divided , Divide into organizations , For example, divide into protection groups , Nutritive tissue , Groom the organization , This can also be understood as the process of dividing the domain into sub domains .

Step four : To further divide the organization , It can be divided into cells , For example, root hair cells 、 Ductal cells and so on

Is it necessary for us to continue to split cells ？ It depends on the business we study , For example, before the light microscope , When it comes to cells, it's over , Specific to other businesses , At a certain stage of research, there is no need to continue to split , And this is the lowest level area , It's usually what we call entities , polymerization 、 Aggregate root 、 Entities, value objects and so on will be further understood later .

Let's summarize the concepts of the nouns mentioned above :

field ： It's often a part of the business , For example, the sales part of e-commerce 、 Logistics part 、 Supply chain, etc , These are all fields for e-commerce ( modular ), The main function of domain is to drive scope , DDD Will limit the scope of the problem to a specific boundary , Building domain models within this boundary , Then the domain model is implemented with code , Solve the corresponding business problems . in short ,DDD The domain of business problem is the domain of business problem to be solved within this boundary .

Subdomain ： A relative concept , We can further divide the fields , This is the subdomain , You can even continue to divide sub domains to form Subdomain ( Still called Subdomain ), It's like when we study plants , If the object of study is peach trees , So fruits, roots and leaves are fields , But if it's not just about fruits , We have to study tissues and even cells , So what we are studying is the subdomain of fruit 、 Subdomains of organizations .

Core domain ： The most critical part of all areas , What does that mean , It's the core part , For business , The core domain is the fundamental competitiveness of enterprises , It's also the most important part of making profits , For example, there are so many fields in e-commerce , What's the most important ？ It's the sales system , No matter you are 2B still 2C, still PDD , These core modules are core domains .

Common domain : In addition to the core domain , Some areas that need to be done by ourselves , For example, authentication 、 Log etc. , Features are parts that can be shared by multiple domains .

Support domain : The least focused area in the business analysis phase of the system , That is, non core domain, non general domain , For example, payment in e-commerce 、 logistics , Just to support the operation of the business , You can even buy other people's services , This kind of domain is the support domain .

It should be noted that , These terms may not be used in the actual design and development of microservices , But it helps to understand DDD The core design ideas and concepts of , And these ideas and ideas in the actual IT Strategic design, business modeling and microservice design can be used for reference .

Why divide the core domain 、 Common domain 、 Support domain ？

You can know from the above , The sub domain that determines the core competitiveness of products and companies is the core domain , It is the main factor of business success and the core competitiveness of the company . There's not much personalized appeal , A common functional subdomain used by multiple subdomains at the same time is a common domain . There is also a functional subdomain that is required , But it does not include the function of determining the core competitiveness of products and companies , It also does not contain sub domains of general functions , It's the support domain .

Compared with these three kinds of subdomains , The core domain is the most important , When we talk about the purpose, we will take the core domain as an example . If the common domain and support domain correspond to the enterprise system , For example , Common domain is the common system you need to use , For example, certification 、 Permissions, etc. , This kind of application is easy to buy , There is no limitation of enterprise characteristics , You don't need to do much customization . The supporting domain has the characteristics of enterprise , But it's not universal , For example, the data dictionary of data code class and other systems .

So why divide these new nouns ？ Think of a question first , For peach trees , root 、 stem 、 leaf 、 flowers 、 Fruit 、 Which of the six seed domains is the core domain ？

Is there a different understanding ？ Some people say seeds , Some people say it's roots , Some say it's a leaf , Some people say it's stems and so on , Why does this happen ？

Because everyone's angle is different , If you're a fruit farmer , So the fruit is the core domain , Most of your operations should be around increasing fruit yield , If you are a scenic spot Administrator , So Fangfei, April peach blossom is your focus , If you are a staff member of the forest farm , So tree trunks should be your focus , You see , For subdomains of the same domain , Everyone has a different understanding , Then we need to determine the core domain through discussion , Make sure everyone agrees , For actual business development , There are many people involved , There are business aspects , There are architects , There are back-end developers , Marketing and so on , We have to identify our core domain from the very beginning , Apart from unifying our understanding, what are the advantages ？

For an enterprise , Budget and time are limited , It means that time, energy and even money should be spent in the core as much as possible . It's like e-commerce , There are so many e-commerce enterprises , Each core domain is different , The market results are also very different , Then the company's strategic focus and business model should find the core domain , And focus on the core domain .

in general , Core domain 、 The main goals of the support domain and the common domain are ： Through domain division , Distinguish the different functions of different subdomains in the company
Attributes and importance , Thus, the company can adopt different resource investment and construction strategies for different sub domains , Their attention will also be different .

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