# declarative programming language

> type of programming language

**Wikidata**: [Q1144882](https://www.wikidata.org/wiki/Q1144882)  
**Source**: https://4ort.xyz/entity/declarative-programming-language

## Summary
A declarative programming language is a type of programming language that follows the declarative programming paradigm to communicate instructions to a machine. Unlike imperative languages, these focus on describing the desired results or logic of a computation without explicitly listing the control flow or steps to achieve them.

## Key Facts
- **Classification:** It is a subclass of "programming language" and includes specialized categories such as RDF query languages and rule-based languages.
- **Programming Paradigm:** It is defined by the declarative programming paradigm.
- **Early Examples:** Notable early instances include ABSYS (1967), Prolog (1972), and Lucid (1976).
- **Logic Programming:** Several declarative languages, such as Prolog and Datalog (1986), are based on first-order logic.
- **Domain-Specific Use:** It is used for diverse applications including cloud resource definition (Azure Bicep), database management (Cypher, EdgeQL), and UI markup (MXML, XAML).
- **Rule-Based Systems:** A specific class of these languages instantiates rules automatically when activated by specific conditions within a data set.
- **Identifiers:** Recognized in KBPedia as `DeclarativeProgrammingLanguage` and in the Google Knowledge Graph as `/g/11bc62dw92`.

## FAQs
### Q: What is the difference between a declarative language and a rule-based language?
A: A rule-based language is a specific type of declarative programming language. While all declarative languages focus on logic over control flow, rule-based languages specifically function by triggering instructions or "rules" only when certain conditions are met within a set of data.

### Q: Which declarative languages are used for databases?
A: Several declarative languages are designed for data management, including Datalog for logic programming, Cypher for Neo4j graph databases, and EdgeQL for relational databases. Additionally, RDF query languages are a specific class used to query RDF graphs.

### Q: Are markup languages considered declarative?
A: Yes, many markup languages function as declarative languages. Examples include MXML and XAML for user interfaces, SMIL for multimedia presentations, and the Mapbox Style Specification for defining map appearances.

## Why It Matters
Declarative programming languages are fundamental to modern computing because they allow developers to express complex logic and data relationships without managing the underlying machine state. By focusing on "what" a program should accomplish rather than "how" to execute every step, these languages reduce the complexity of tasks like database querying, knowledge representation, and system configuration.

The significance of this paradigm is evident in its widespread adoption across specialized fields. In infrastructure, languages like Azure Bicep and Azure Resource Manager allow for the consistent definition of cloud environments. In data science and graph theory, languages like Cypher and Datalog provide powerful tools for navigating complex data structures. Furthermore, the paradigm supports cross-platform development and authorization orchestration through tools like GeneXus and IDQL. By abstracting the execution details, declarative languages enable more concise, readable, and maintainable code, which is essential for managing the scale of modern software systems and data architectures.

## Notable For
- **Logic-Based Foundations:** Includes languages like Prolog (1972) and Datalog (1986) that utilize first-order logic for programming.
- **Infrastructure as Code:** Features domain-specific languages like Azure Bicep and Azure Resource Manager for defining cloud resources.
- **Data Format Specification:** Includes specialized tools like Kaitai Struct, a declarative language specifically for defining binary data formats.
- **Knowledge Representation:** Supports development tools like GeneXus (1988), which is based on knowledge representation for cross-platform development.

## Body

### Historical Development and Logic Programming
The history of declarative programming is marked by the development of logic-based systems. **ABSYS**, appearing in 1967, is one of the earliest examples of a declarative language. This was followed by **Prolog** in 1972, which introduced a paradigm based on first-order logic. In 1986, **Datalog** emerged as a declarative logic programming language, later spawning fragments such as linear Datalog, guarded Datalog, and frontier-guarded Datalog.

### Specialized Classifications
Declarative languages are often categorized by their specific functional goals:
*   **Rule-based languages:** These languages instantiate rules when activated by conditions in a data set.
*   **RDF query languages:** A class of languages designed specifically for querying RDF graphs.
*   **Markup and UI Languages:** This group includes **MXML** (2004), **XAML** (2008), and **SMIL**, which use XML-based structures to define interfaces and presentations.

### Domain-Specific Implementations
Modern declarative languages are frequently domain-specific:
*   **Cloud and Policy:** **Azure Bicep** and **Azure Resource Manager** define cloud infrastructure, while **IDQL** orchestrates cross-platform authorization policies.
*   **Database and Graph Querying:** **Cypher** is used for Neo4j graph databases, while **EdgeQL** and **.QL** (2007) provide object-oriented or relational database management.
*   **Data and Styling:** The **Mapbox Style Specification** and **MapLibre Style Specification** use JSON-based formats to define map content and appearance. **Kaitai Struct** provides a declarative way to specify binary data formats.

### General Purpose and Environment-Based Languages
Some declarative languages serve broader programming or modeling needs. The **Wolfram Language** (1988) provides a comprehensive programming environment, while **Modelica** (1997) and its open-source environment **Openmodelica** are used for modeling complex systems. Other notable entries include **Lucid** (1976), **Harbour** (1999), and **Curl** (1998).

## Schema Markup
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## References

1. KBpedia