kdl/SCHEMA-SPEC.md

KDL Schema Specification

The KDL Schema specification describes a schema language for use with KDL, written in KDL itself. A schema language allows users to describe and constrain the allowed semantics of a KDL document. This can be used for many purposes: documentation for users, automated verification, or even automated generation of bindings!

The Formal Schema

For the full KDL Schema schema itself, see examples/kdl-schema.kdl.

Definition

document node

This is the toplevel node in a KDL Schema. It is required, and there must be exactly one, at the very toplevel of a document.

Values

None.

Properties

• description (optional): An informational description of the purpose of this schema.
• schema-url (optional): A URL where someone may go to find more information about this schema. It is not meant for mechanical processing.

Children

• node - zero or more toplevel nodes for the KDL document this schema describes.

node node

The node node describes node instances in a document. These may either be at the toplevel of the document, or they may be nested inside a children block in another node.

Values

• Node name (optional) - A string name for the node. If present, the node's rules/validations will apply only to children with this node name. Otherwise, the rules will apply to all child nodes, regardless of whether they're named or not.

Properties

• description (optional): An informational description of the purpose of this node.
• id (optional): A globally unique identifier for this node.
• ref (optional): A globally unique reference to another node's ID. If present, all properties, values, and children defined in the target node will be copied to this node, replacing any conflicts.

Children

• min (optional): Minimum number of this kind of node (or any node, if the name is missing) allowed in the parent's children block.
• max (optional): Maximum number of this kind of node (or any node, if the name is missing) allowed in the parent's children block.
• prop - zero or more properties for this node.
• value - zero or more values for this node.
• children - zero or more children for this node.

prop node

Represents a property of a node, which is a key/value pair in KDL.

Values

• key (optional) - String key for the property. If this value is missing, the prop node's attributes will apply to all properties of its parent.

Properties

• description (optional): An informational description of the purpose of this property.
• id (optional): A globally unique identifier for this property.
• ref (optional): A globally unique reference to another property's ID. If present, all properties defined in the target property will be copied to this property, replacing any conflicts.

Children

• type (optional): A string denoting the type of the property value.
• enum (optional): A specific list of allowed values for this property. May be heterogenous as long as it agrees with the type, if specified.
• required (optional): A boolean value indicating whether this property is required.

value node

Used to describe one or more values for a KDL node.

Values

None.

Properties

• description (optional): An informational description of the purpose of this value.
• id (optional): A globally unique identifier for this value.
• ref (optional): A globally unique reference to another value's ID. If present, all values defined in the target value will be copied to this value, replacing any conflicts.

Children

• type (optional): A string denoting the type of the value.
• enum (optional): A specific list of allowed values for this value. May be heterogenous as long as it agrees with the type, if specified.
• min (optional): Minimum number of values allowed.
• max (optional): Maximum number of values allowed.

children node

Denotes KDL node children.

Values

None.

Properties

• description (optional): An informational description of the purpose of this children block.
• id (optional): A globally unique identifier for this children block.
• ref (optional): A globally unique reference to another children block's ID. If present, all children defined in the target children block will be copied to this children block, replacing any conflicts.

Children

• node - zero or more child nodes.