feat: ddd intro

courses/itmo-software-design/domain-driven-design.md

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-# todo
+### Domain Driven Design
+
+DDD is an approach to designing systems, usually software, that emphasises creating a common 
+language between domain experts and system builders.
+
+![](./docs/ddd/ddd.jpeg)
+
+> It's a way of thinking about software development that focuses on the business 
+> problem being solved and the domain of the business problem.
+> 
+> It's not a technology or a methodology. It's a way of thinking about how you build and 
+> design your software.
+>
+> - Eric Evans
+
+**Domain** - an area of interest or an area over which a person has control.
+> A domain is an arbitrary boundary around some subset of concepts in the universe.
+>
+> They are subjective and aren't mutually exclusive.
+
+![](./docs/ddd/domains.webp)
+
+When modelling systems we have to choose the most appropriate domain boundaries with which to align our software and organisational boundaries.
+
+**Subdomain** - a domain within a larger domain.
+
+**Ubitiquitous Language** - a language structured around the domain model and used by 
+all team members to connect all the activities of the team with the software.
+
+![](./docs/ddd/ubiquitous-language.png)
+
+**Bounded Context** - distinct area within a business domain where concepts, language and 
+rules are clearly defined and consistent.
+
+![](./docs/ddd/bc.jpeg)
+
+> Ideal way: when single subdomain matches a single bounded context.
+>
+> But still can have multiple bounded contexts within a single subdomain.
+
+