Entities are real-world concepts in a business such as customers, transactions, and ad campaigns. We often focus our analyses around specific entities, such as customer churn or annual recurring revenue modeling. We represent entities in our semantic models using id columns that serve as join keys to other semantic models in your semantic graph.
Within a semantic graph, the required parameters for an entity are
name refers to either the key column name from the underlying data table, or it may serve as an alias with the column name referenced in the
expr parameter. The
name for your entity must be unique to the semantic model and can not be the same as an existing
dimension within that same model.
Entities can be specified with a single column or multiple columns. Entities (join keys) in a semantic model are identified by their name. Each entity name must be unique within a semantic model, but it doesn't have to be unique across different semantic models.
There are four entity types: primary, foreign, unique, or natural.
You can also use entities as a dimensions, which allows you to aggregate a metric to the granularity of that entity.
MetricFlow's join logic depends on the entity
type you use, and it also determines how to join semantic models. Refer to Joins for more info on how to construct joins.
- Primary — A primary key has only one record for each row in the table, and it includes every record in the data platform.
- Unique — A unique key contains only one record per row in the table, but it may have a subset of records in the data warehouse. It can also include nulls.
- Foreign — A foreign key can include zero, one, or multiple instances of the same record. Null values may also be present.
- Natural — Natural keys are column or combination of columns in a table that uniquely identify a record based on real-world data. For instance, in a sales_person_department dimension table, the sales_person_id can serve as a natural key.
The complete spec for entities is below:
- name: transaction ## Required
type: primary or natural or foreign or unique ## Required
description: a description of the field or role the entity takes in this table ## Optional
expr: the field that denotes that entity (transaction_id). ## Optional
If not specified will default to name
Here's an example of how to define entities in a semantic model:
- name: transaction
- name: order
- name: user
expr: substring(id_order from 2)