声明式语言包包括数据库查询语言（SQL，XQuery），正则表达式，逻辑编程，函数式编程和组态管理系统。
声明式编程透过函数、推论规则或项重写（term-rewriting）规则，来描述变量之间的关系。它的语言运行器（编译器或解释器）采用了一个固定的算法，以从这些关系产生结果。
https://baike.baidu.com/item/声明式编程/9939512
Aren’t We Just Hiding the Implementation?
Eventually, every piece of our code must be implemented somewhere. In declarative languages, the implementation is up to whoever interprets the code:
- SQL is handled by a database engine.
- A browser will interpret HTML.
- A YAML configuration file could be handled by a build server.
When we apply some declarative techniques to our imperative languages, it’s up to us to provide the implementation. Even the LINQ extension methods are implemented in C#, they’re just not in our own codebase. So we’re actually just abstracting away implementation details. Then the question is: how far do we go with this abstraction? You will need to find what works best for you, but a good starting point for me is that public methods (i.e. your public API) should contain a minimum set of statements, and these should all be easily readable. The contents of your public method should tell you what is happening, not how.
https://blog.ndepend.com/declarative-programming-depth/