An External Domain-Specific Language (DSL) is a programming language that is separate from general-purpose programming languages and specifically designed to address the requirements of a particular domain or problem space. It’s created with the purpose of providing a specialized tool for users who are not necessarily skilled programmers but need to work within a specific area.

Here are some characteristics of an external DSL:

  1. Separate Syntax: An external DSL has its own syntax that is distinct from general-purpose languages. This syntax is tailored to the specific needs of the targeted domain.
  2. Domain-Specific Abstractions: The language includes constructs, keywords, and abstractions that align closely with the concepts of the domain it serves. This makes it easier for domain experts to express their intentions without delving into the complexities of a general-purpose language.
  3. Specialized Tools: External DSLs often come with tools that can process the DSL code and generate executable code or perform specific actions. These tools can validate the DSL code, optimize it, and transform it into the desired output.
  4. Ease of Use: External DSLs are designed to be user-friendly for individuals who are not necessarily programmers. This allows domain experts to directly interact with and manipulate the system using a language that’s familiar to them.
  5. Increased Productivity: Because external DSLs are tailored to specific tasks, users can work more efficiently within the domain. The DSL’s constructs and abstractions allow for concise and expressive code.
  6. Clear Communication: External DSLs use terminology and syntax that resonate with domain experts. This simplifies communication between technical and non-technical stakeholders.
  7. Focus on the Domain: External DSLs abstract away technical details unrelated to the domain, allowing users to concentrate on solving domain-specific problems.

Examples of external DSLs include SQL (Structured Query Language) for database queries, VHDL (VHSIC Hardware Description Language) for describing digital circuits, and Regular Expressions for pattern matching in strings. These languages empower users to work effectively within their specific domain without requiring them to be experts in general-purpose programming languages.