# Lesson 5: Defining schemas ## [](#_defining_individual_types)[Defining individual types](../5.1-defining-individual-types/index.md) * **Define queries** are used to define new types, interfaces, and functions. They comprise a `define` clause only. Define queries are run **schema transaction**. ```typeql define # define clause ``` * A `entity`, `relation`, or `attribute` kind statement is used to define a new type. You can use `sub` to attach new types to other types as a subtype. ```typeql entity-type sub entity; ``` * Define queries cannot contain variables, only keywords and type labels. * A `relates` statement is used to define a new role for a relation type. All relation types must have at least one role defined. ```typeql relation-type relates role; ``` * A `plays` statement is used to define a new role player for a role. ```typeql entity-type plays role; ``` * A `value` statement is used to define the value type of an attribute type. All attribute types must have a value type defined. ```typeql attribute-type value boolean; ``` * An `owns` statment is used to define a new owner of an attribute type. ```typeql entity-type owns attribute-type; ``` ## [](#_defining_type_hierarchies)[Defining type hierarchies](../5.2-defining-type-hierarchies/index.md) * A **type hierarchy** can be defined by using an existing type using a `sub` statement. ```typeql entity-type sub supertype; ``` * A subtype of an entity or relation type will **inherit** all of its owned attributes and played roles. * An `@abstract` annotation is used to define a type as **abstract**. ```typeql entity-type @abstract; ``` * By default, a subtype of a relation type will inherit all of its roles. Inherited roles can be overridden using the `as` keyword. An overriding role is the subtype of the role it overrides. ```typeql relation-type relates role as overridden-role; ``` ## [](#_defining_data_constraints)[Defining data constraints](../5.3-defining-constraints/index.md) * A `@card` annotation controls the connectivity of your dataset * A `@regex` annotation can be used to constrain string attribute type by regex * A `@values` annotation can be used to constrain any value type to set a possible values * A `@range` annotation can be used to constraint any numerical value type ```typeql attribute attribute-type @regex("^regex pattern$"); ``` * A `@key` annotation is used to define a **key constraint** on an attribute ownership, requiring that instances of the owner type own exactly one instance of the attribute type, and that it must be uniquely owned by the owner type. ```typeql entity-type owns attribute-type @key; ``` * A `@unique` annotation is used to define a **unique constraint** on an attribute ownership, requiring that instances of the attribute type are uniquely owned by the owner type. ```typeql entity-type owns attribute-type @unique; ``` ## [](#_defining_functions)[Defining functions](../5.4-defining-functions/index.md) * A function definition has three components: a **signature**, a **body**, and a **return**. ```typeql fun function-name($arg: arg-type) -> { return-type }: return ; ``` * The body can be any read-only query pipeline * The return operation must match the declared signature ## [](#_schema_validation)[Schema validation](../5.5-schema-validation/index.md) * Checks must be passed whenever changes to the schema are made to ensure internal consistency. * Making changes that fail a validation check will cause an exception to be thrown. ## [](#_further_learning)Further learning [Lesson 6: Building applications](../../6-building-applications/index.md) Learn how to build applications on TypeDB, covering database management, transaction control, and result stream processing. [Lesson 7: Understanding query patterns](../../7-understanding-query-patterns/index.md) Learn how to build query patterns utilising advanced elements of TypeQL syntax, and how queries are resolved by TypeDB. [Reference: Defining schemas](../../../typeql-reference/schema/index.md) Learn more about defining schemas for TypeDB, covering Define queries, Undefine queries, and schema editing. [Schema validation](../5.5-schema-validation/index.md) [6\. Building applications](../../6-building-applications/index.md) [Edit on GitHub](https://github.com/typedb/typedb-docs/edit/3.x-development/academy/modules/ROOT/pages/5-defining-schemas/summary.adoc) Edit this page on GitHub.