What is a knowledge graph, and how does Heidi use one?
A knowledge graph stores knowledge as entities and their relationships, people, companies, projects, systems, connected by facts. Heidi's Cortex is a typed knowledge graph, which is why she can answer questions that span systems.
A search index finds documents. A graph answers questions: who is the champion at this customer, which contracts does this setting touch, what decision preceded this incident. The connections are the knowledge.
Every node and edge keeps sources and permissions, so graph answers stay as accountable as everything else Heidi says.