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Implementing Domain-Driven Design by Vaughn Vernon

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Standard Types Expressed as Values

In many systems and applications there is a need for what I call Standard Types. Standard Types are descriptive objects that indicate the types of things. There is the thing (Entity) or description (Value) itself, and there are also the Standard Types to distinguish them from other types of the same thing. I am unaware of an industry standard name for this concept, but I have also heard it called a type code and a lookup. The name type code doesn’t say much. And a lookup is a lookup of what? I prefer the name Standard Types because it is more descriptive. To make this concept clearer, consider a few uses. In some cases these are modeled as Power Types.

Your Ubiquitous Language defines a PhoneNumber (Value), ...

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