Declarative programming

A programming paradigm that describes desired results or properties of a computation rather than prescribing the sequence of steps that produces them.

Imperative programming: A programming paradigm that specifies computations as explicit commands and state changes. It makes the step-by-step control flow that declarative programs leave implicit explicit.
Expression (computer science): A syntactic construct that evaluates to a value. Expressions let a program state what value is wanted rather than command each operation.
SQL: A language for defining, querying, and manipulating data in relational database systems. A SQL query states which rows and columns are wanted, not the retrieval procedure.
Interpreter (computing): A program that executes or evaluates instructions expressed in a programming language. Declarative languages commonly rely on interpreters to evaluate descriptions according to defined semantics.
Referential transparency: A property whereby an expression can be replaced by its value without changing program behavior. This property makes many declarative expressions easier to reason about and transform safely.
Procedural programming: A programming paradigm that organizes programs as procedures containing ordered instructions. It expresses computation through ordered procedures rather than primarily through desired outcomes.
Constraint satisfaction problem: A problem defined by variables, possible values, and constraints that valid assignments must satisfy. Constraint-based programs state conditions on acceptable solutions for a solver to satisfy.
HTML: A markup language that structures content for web pages. HTML describes document structure and meaning while browsers decide how to render it.
Query optimizer: A database component that selects an execution plan for a query. It chooses an efficient procedure while preserving the result specified by a declarative query.
Program optimization: The transformation of a program to improve qualities such as speed or memory use while preserving behavior. A declarative description can give an optimizer more freedom to choose execution strategies.

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