Lesson 5.1: Defining individual types

In TypeDB, all databases have a schema that provides semantic integrity guarantees for inserted data and enables the resolution of polymorphic queries. A schema is created using Define queries, which are each composed of a single define clause. We’ll start with the syntax for defining entity types, then look at relation types and attribute types.

The following is an example of a Define query that defines four new entity types.

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Using a schema session and a write transaction, try running this query on a newly created database. After running it, make sure to commit the transaction. You should see the four new entity types appear in the type browser.

When used in a Define query, a sub statement defines a new type. The subject of each statement is the new type label, and the object is one of the three root types: entity, relation, or attribute, indicating which kind of type is being defined.

When sub statements are used in a Define query, they are data definition statements. This is in contrast to when used in other kinds of query, as we saw in Lesson 3.4, in which they are data manipulation statements. Define queries comprise only data definition statements, and so cannot contain any variables. The only permitted terms are keywords and type labels.

The syntax for defining new relation types is the same as that used to define entity types, but each relation type must be defined alongside at least one role. The following query defines three new relation types along with their roles.

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When used in a Define query, the relates keyword defines a new role for a relation type. This query defines the following relation types:

In this case, rating and order-line are binary relation types, while publishing is a ternary relation type. There is no limit to the number of roles that can be defined for a relation type using the relates keyword.

Once relation types and their roles have been defined, we can declare which types play roles.

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When used in a Define query, the plays keyword defines a new roleplayer for a relation’s role (i.e. a new implementer of a role interface).

Whereas relations must be defined with roles, attributes must be defined with value types. The following query defines five new attribute types.

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When used in a Define query, the value keyword defines the value type of an attribute type. When the attribute type is later instantiated, its values must be of the specified value type. There are currently five value types in TypeDB:

More value types will be added in future updates.

With attribute types defined, we can now declare which types own which attributes.

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When used in a Define query, the owns keyword defines a new attribute owner (i.e. a new implementer of an ownership interface). The syntax is the same for declaring entity types (like user) and relation types (like order-line) as owners.