A __knowledge graph__ is a knowledge base that uses a graph-structured data model or topology to integrate data. Knowledge graphs are often used to store interlinked descriptions of Named entity with free-form semantics - wikipedia 
Since the development of the Semantic Web, knowledge graphs are often associated with linked data projects, focusing on the connections between concepts and entities. They are also prominently associated with and used by search engines such as Google Knowledge Graph, Bing (search engine), and Yahoo; knowledge-engines and question-answering services such as WolframAlpha, Apple's Siri, and Amazon Amazon Alexa; and social networks such as LinkedIn and Facebook.
# Using a knowledge graph for reasoning over data
A knowledge graph formally represents semantics by describing entities and their relationships. Knowledge graphs may make use of Ontology (information science) as a schema layer. By doing this, they allow Inference for retrieving implicit knowledge rather than only allowing queries requesting explicit knowledge - wikipedia
In order to allow the use of knowledge graphs in various machine learning tasks, several methods for deriving latent feature representations of entities and relations have been devised. These knowledge graph embeddings allow them to be connected to machine learning methods that require feature vectors like word embeddings. This can complement other estimates of conceptual similarity.
# Definitions
There is no single commonly accepted definition of a knowledge graph. Most definitions view the topic through a Semantic Web lens and include these features: - wikipedia
- ''Flexible relations among knowledge in topical domains:'' A knowledge graph (i) defines abstract classes and relations of entities in a schema, (ii) mainly describes real world entities and their interrelations, organized in a graph, (iii) allows for potentially interrelating arbitrary entities with each other, and (iv) covers various topical domains. - ''General structure'': A network of entities, their semantic types, properties, and relationships. - ''Supporting reasoning over inferred ontologies'': A knowledge graph acquires and integrates information into an ontology and applies a reasoner to derive new knowledge. - A digital structure that represents knowledge as concepts and the relationships between them (facts). A knowledge graph can include an ontology that allows both humans and machines to understand and reason about its contents.
In addition to the above examples, the term has been used to describe open knowledge projects such as YAGO and Wikidata; federations like the Linked Open Data cloud; a range of commercial search tools, including Yahoo’s semantic search assistant Spark, Google’s Knowledge Graph, and Microsoft’s Satori; and the LinkedIn and Facebook entity graphs. The term is also increasingly used by note taking applications allowing a user to build their personal knowledge graph.
The term is also increasingly used by note taking applications allowing a user to build their personal knowledge graph.
# See also