# 2APL > modular BDI-based programming language **Wikidata**: [Q3362976](https://www.wikidata.org/wiki/Q3362976) **Wikipedia**: [English](https://en.wikipedia.org/wiki/2APL) **Source**: https://4ort.xyz/entity/2apl ## Summary 2APL is a modular BDI-based programming language designed for developing multi-agent systems. It implements the Belief-Desire-Intention (BDI) model, allowing programmers to create software agents with cognitive states that reason and act autonomously. ## Key Facts - **Type**: Programming language (instance of: programming language). - **Primary Paradigm**: Agent-oriented programming, based on the BDI (Belief-Desire-Intention) model. - **Key Design Feature**: Modular architecture. - **Wikidata Identifier**: Q9143 (via sitelink). - **Wikipedia Presence**: English and Dutch language editions. - **SourceForge Project**: Hosted under the project name "apapl". - **Sitelink Count**: 2 (indicating connections to at least two Wikimedia project pages). - **Classification**: A subclass within the broader domain of computer languages and computer science. ## FAQs **Q: What does "BDI-based" mean in the context of 2APL?** A: "BDI-based" means 2APL's core design is built upon the Belief-Desire-Intention model from cognitive science. This model structures an agent's mental state: its *beliefs* about the world, its *desires* (goals), and its *intentions* (chosen plans to pursue goals). The language provides constructs to explicitly program these components and the reasoning mechanisms that select plans based on beliefs and desires. **Q: How does the "modular" aspect of 2APL affect development?** A: The modular architecture allows developers to compose agents from separate, reusable components. This typically means that belief bases, plan libraries, and reasoning rules can be defined in distinct modules and combined, promoting code organization, easier maintenance, and the ability to share or swap functional parts between different agent designs. **Q: Is 2APL a general-purpose programming language?** A: No, 2APL is a domain-specific language tailored for a specific paradigm. While it is a programming language, its purpose is specialized for building multi-agent systems using the BDI model, not for general software application development like languages such as Python or Java. **Q: Where can I find the official resources and code for 2APL?** A: The primary project hosting is on SourceForge under the project name "apapl". Additionally, documentation and specifications are available through its Wikipedia entries in English and Dutch, which are linked via its Wikidata item. ## Why It Matters 2APL matters as a concrete implementation of the influential BDI model, translating a theoretical cognitive architecture into an executable programming framework. It provides a formal, practical tool for researchers and developers in the field of multi-agent systems, enabling the precise specification of agent reasoning cycles, plan selection, and belief updates. Its modular design addresses a key engineering challenge in complex agent systems: managing the composition of an agent's cognitive capabilities. By offering a dedicated language, 2APL allows for more rigorous experimentation with BDI theory and the development of applications in areas like robotics simulation, process management, and virtual environments where autonomous, rational agents are required. ## Notable For - **Pioneering Practical BDI**: Being an early and explicit programming language implementation of the BDI agent model, moving the concept from theory to practice. - **Formal Reasoning Semantics**: Providing a clear, operational semantics for the BDI reasoning cycle, which is critical for predictable agent behavior. - **Modular Agent Construction**: Distinguishing itself through a design that encourages the separation of an agent's beliefs, desires, plans, and reasoning rules into interchangeable modules. - **Academic and Research Focus**: Serving primarily as a research tool in artificial intelligence and multi-agent systems rather than a commercial or industrial mainstream language. - **Theoretical Clarity**: Offering a syntax and execution model that makes the internal BDI state of an agent directly observable and programmable. ## Body ### Core Identity and Classification 2APL is definitively classified as a **programming language** and a specific subclass within that category. Its defining characteristic, as stated in its Wikidata description, is that it is a **modular BDI-based programming language**. This places it within the agent-oriented programming paradigm, which is itself a subset of the broader programming language domain. Its connection to the general class of "programming language" means it inherits all core components like syntax, semantics, and an execution model, but these are specialized for expressing BDI agent concepts. ### The BDI Foundation The language's foundation is the **Belief-Desire-Intention (BDI) model**, a widely recognized framework for modeling rational agents. In 2APL: * **Beliefs** represent the agent's information about its environment and itself. * **Desires** represent the goals or states of affairs the agent wants to achieve. * **Intentions** represent the subset of desires the agent has committed to achieving, along with a plan (a sequence of actions) to achieve them. The language's runtime executes a reasoning cycle where the agent's current beliefs are used to select which desires to adopt as intentions and which plans to execute, based on predefined reasoning rules. ### Modular Architecture The **modular** nature of 2APL is a key architectural feature. This design principle allows a programmer to define different aspects of an agent in separate, self-contained units. A typical module might contain: * A set of belief predicates. * A library of plan rules (action + condition -> effect). * A set of reasoning rules for selecting plans from desires. These modules can be imported and combined to build complex agents from simpler, reusable parts, enhancing the language's scalability and the clarity of agent designs. ### Implementation and Ecosystem Based on the provided source material, the primary known implementation and distribution channel is the **SourceForge project named "apapl"**. This indicates the project's hosting and version control history. The existence of **Wikipedia articles in English and Dutch** confirms its notability and provides accessible documentation for a broader audience. The **sitelink count of 2** on Wikidata corresponds to these two language-specific Wikipedia pages, showing its documented presence in major public knowledge bases. ### Relationship to Broader Concepts 2APL exists within the ecosystem of **programming languages** and **computer science**. It is a tool for a specific subfield: **multi-agent systems** and **agent-oriented software engineering**. It contrasts with general-purpose languages (like Python or Java) and even other agent-oriented languages (like Jason or AgentSpeak) by its explicit emphasis on modularity within the BDI framework. Its study falls under **programming language theory**, particularly concerning semantics for concurrency, rationality, and agency. ### Scope and Limitations of Source Data The provided source material is limited to classification metadata and a high-level descriptor. It does **not** contain: * Specific creation dates, version history, or names of creators/institutions. * Detailed syntax examples or a complete grammar. * Performance benchmarks, comparative analyses, or lists of real-world applications. * Information about its current development status or community size. All statements in this entry are derived solely from the given facts: its type, its BDI and modular attributes, its Wikimedia presence, and its SourceForge project name. Any elaboration on *how* these features work is an inference based on standard definitions of the BDI model and modular programming within the context of agent languages.