> ## Documentation Index
> Fetch the complete documentation index at: https://docs.a1facts.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Ontology

> The ontology is the backbone of your knowledge graph. It defines the schema for your data.

The ontology is a declarative `YAML` file that defines the structure of your knowledge graph. It specifies the types of entities and relationships that can exist in your graph, acting as a schema to ensure data consistency and to guide the query generation process.

By defining a clear and explicit ontology, you enable `a1facts` to validate incoming data and construct precise queries.

## Example

Here is an example of an ontology for financial analysis, taken from the [Stock Analysis](/cookbook/stock-analysis) cookbook example.

```yaml company.yaml theme={null}
name: company_info
description: "Ontology for company information"
entities:
  - name: Company
    description: "A company"
    properties:
      - name: name
        type: string
        description: "The name of the company"
      - name: ticker
        type: string
        description: "The stock ticker of the company"
      - name: description
        type: string
        description: "A description of the company"
  - name: Product_Service
    description: "A product or service offered by a company"
    properties:
      - name: name
        type: string
        description: "The name of the product or service"
  - name: Market
    description: "A market that a company operates in"
    properties:
      - name: name
        type: string
        description: "The name of the market"
relationships:
  - name: competes_with
    description: "A company competes with another company"
    domain: Company
    range: Company
  - name: offers
    description: "A company offers a product or service"
    domain: Company
    range: Product_Service
  - name: operates_in
    description: "A company operates in a market"
    domain: Company
    range: Market
```

## Key Concepts

The ontology is defined by the following key concepts, which are organized into a hierarchical structure in the YAML file.

<AccordionGroup>
  <Accordion title="`name`">
    **Type:** `string`

    The top-level name of the ontology, used to identify it.
  </Accordion>

  <Accordion title="`description`">
    **Type:** `string`

    A brief description of the ontology's purpose and scope.
  </Accordion>

  <Accordion title="`entities`">
    **Type:** `list`

    A list of entity types that can exist in the knowledge graph. Each entity represents a class of objects.

    <Expandable title="Entity Properties">
      <ResponseField name="name" type="string" required>
        The name of the entity type (e.g., `Company`, `Product_Service`).
      </ResponseField>

      <ResponseField name="description" type="string">
        A short description of the entity type.
      </ResponseField>

      <ResponseField name="properties" type="list">
        A list of properties associated with the entity type. Each property defines an attribute of the entity.

        <Expandable title="Property Attributes">
          <ResponseField name="name" type="string" required>
            The name of the property (e.g., `ticker`, `description`).
          </ResponseField>

          <ResponseField name="type" type="string" required>
            The data type of the property (e.g., `string`, `integer`).
          </ResponseField>

          <ResponseField name="description" type="string">
            A description of the property.
          </ResponseField>
        </Expandable>
      </ResponseField>
    </Expandable>
  </Accordion>

  <Accordion title="`relationships`">
    **Type:** `list`

    A list of relationship types that define how entities can be connected.

    <Expandable title="Relationship Properties">
      <ResponseField name="name" type="string" required>
        The name of the relationship type (e.g., `competes_with`, `offers`).
      </ResponseField>

      <ResponseField name="description" type="string">
        A short description of what the relationship represents.
      </ResponseField>

      <ResponseField name="domain" type="string" required>
        The source entity type of the relationship.
      </ResponseField>

      <ResponseField name="range" type="string" required>
        The target entity type of the relationship.
      </ResponseField>
    </Expandable>
  </Accordion>
</AccordionGroup>