What is a knowledge graph?

A knowledge graph is a structured way to represent information by connecting entities (like people, places, or concepts) and their relationships. It organizes data as a network of nodes (entities) and edges (relationships), often stored in a graph database or triple store. Unlike traditional databases that rely on tables, knowledge graphs emphasize connections between data points, making them useful for modeling complex, real-world scenarios. For example, a knowledge graph could link “Albert Einstein” to “Theory of Relativity” with a “developed” relationship, and “Theory of Relativity” to “Physics” with a “field_of_study” relationship. This structure allows queries that traverse relationships, such as finding all scientists who contributed to a specific field.

From a technical perspective, knowledge graphs often use standards like RDF (Resource Description Framework) to model data as triples (subject-predicate-object). Tools like Apache Jena or graph databases like Neo4j provide frameworks to build and query these structures. Ontologies—formal definitions of entity types and relationships—are used to enforce consistency. For instance, an e-commerce system might define an ontology where a “Product” has attributes like “price” and “category,” and is linked to a “Manufacturer” via a “produced_by” relationship. SPARQL, a query language for RDF, lets developers retrieve data by traversing these connections. For example, a query could find all products under $50 made by manufacturers in a specific region, leveraging both attribute filters and relationship paths.

Knowledge graphs are practical in applications requiring data integration or contextual analysis. Search engines use them to understand user queries and return precise answers (e.g., Google’s Knowledge Panel). In recommendation systems, they identify related items by analyzing connections—like suggesting movies based on shared actors or genres. Enterprises use them to unify data from disparate sources, such as linking customer records to purchase histories stored in separate databases. Developers can implement knowledge graphs using open-source tools (e.g., RDFLib for Python) or cloud services like AWS Neptune. For example, a healthcare app might build a knowledge graph to model relationships between patients, treatments, and medical studies, enabling queries like “Which treatments for Condition X have the fewest side effects?” This approach turns isolated data into a navigable web of insights.