Wikidata
Wikidata is a free, collaborative knowledge base that serves as a central storage repository for structured data used across Wikimedia projects like Wikipedia. Think of it as a massive, machine-readable database where facts about the world are stored in a standardized format. Instead of having the same information scattered across different language versions of Wikipedia articles, Wikidata centralizes this data so it can be shared and updated once for use everywhere. For example, when you see a Wikipedia infobox showing someone's birth date, occupation, or nationality, that information often comes directly from Wikidata.
What makes Wikidata special is its collaborative nature—anyone can contribute and edit the data, similar to Wikipedia articles. The platform stores facts as statements that include not just the information itself, but also sources and qualifiers that provide context. This means you might find that "Paris is the capital of France" along with references to support this claim and additional details like when this became true. Wikidata currently contains over 100 million items covering everything from people and places to concepts and events.
The structured nature of Wikidata makes it incredibly useful for applications beyond just Wikipedia. Researchers, developers, and organizations use it to power everything from search engines and chatbots to academic research and data visualization projects, making it one of the largest freely available knowledge graphs in the world.
Building on the basic concept, Wikidata operates on a sophisticated data model built around entities, properties, and statements. Each item in Wikidata has a unique identifier (like Q90 for Paris) and can have multiple statements describing its properties. These statements follow a subject-predicate-object structure: for instance, "Paris (Q90) → capital of (P36) → France (Q142)." Properties themselves are also items with their own identifiers, creating a self-describing system where the schema is part of the data.
The platform supports complex data types including not just simple text and numbers, but also geographical coordinates, dates with varying precision, media files, and relationships to other Wikidata items. Statements can include qualifiers that add context (like "from 1958" for when Paris became capital) and references that cite sources. This rich metadata structure allows for nuanced representation of real-world complexity, including conflicting viewpoints and temporal changes.
Wikidata uses a **multilingual approach **where labels, descriptions, and aliases can exist in hundreds of languages, but the underlying data structure remains language-independent. This separation allows the same factual information to be presented in different languages without duplication. The platform also implements a robust system of ranks (preferred, normal, deprecated) to handle multiple values for the same property and uses constraint checking to maintain data quality across its massive scale.
From a developer perspective, Wikidata exposes its vast knowledge graph through multiple APIs and data formats. The primary Wikidata REST API provides programmatic access to items, properties, and statements with endpoints like /entities/{entity_id} for retrieving complete item data and /entities/{entity_id}/statements for specific properties. The API supports both JSON and RDF serialization formats, with JSON being more developer-friendly and RDF better suited for semantic web applications.
For more complex queries, the SPARQL Query Service at query.wikidata.org allows developers to run sophisticated graph queries across the entire dataset. SPARQL queries can traverse relationships, aggregate data, and perform complex filtering operations that would require multiple REST API calls. The service includes a web interface for testing queries and supports various output formats including JSON, CSV, and XML. Rate limiting is implemented but generous for most use cases, though bulk data access should use the regular data dumps.
Integration patterns typically involve either real-time API calls for dynamic applications or periodic synchronization using data dumps for applications requiring local data storage. The MediaWiki Action API provides additional functionality for authentication, editing, and administrative operations, while the EntitySchema extension allows validation of data structure. Wikidata's linked data architecture means items reference each other extensively, so effective integration often requires understanding the graph structure and implementing strategies for resolving entity relationships. Authentication via OAuth is required for write operations, and all edits are logged and reversible, making it suitable for automated data contribution workflows. For more about this explicit setup, see Oauth.
Key endpoints include:
Special:EntityData/{ID}: Direct entity data access
wbgetentities: MediaWiki API for batch entity retrieval
wbsearchentities: Entity search functionality
SPARQL endpoint: Complex querying at https://query.wikidata.org/sparql