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KDL Data Model
This document specifies an abstract data model of KDL document language.
This is version 0.0.0 of KDL Data model. It has not been released yet.
Introduction
KDL is defined by KDL Specification as a formal language with components such as nodes, identifiers, strings, comments, and whitespace. Some of these components can be expressed in mutliple ways and some of these components are typically ignored when a KDL document is parsed.
KDL Data model defines a conceptual structure of semantically relevant elements expressed in KDL syntax. The data model is required to process KDL documents independent from syntax and implementations with KDL Query Language and KDL Schema Language.
Elements
Every KDL document represents a document.
Sequences and sets can be empty.
A Unicode string is a sequence of Unicode code points.
Document
A document is a sequence of nodes.
Documents must not contain itself via node direct or indirect children to avoid circular structures.
Node
A node consists of three mandatory and two optional elements:
- a name being a Unicode string
- an optional tag being a Unicode string
- a sequence of arguments, each being a value
- a set of properties, each consisting of
- a name being Unicode string unique within the set
- a value
- an optional list of children being a document
Value
A value is one of:
- a Unicode string
- a number, consisting of an integer part and a decimal part
- a boolean, being one of the special values true and false
- the special value null
Application Notes
Implementations may want to limit the set of processable KDL documents by limiting properties of the data model such as the following:
-
A node with empty string tag (e.g.
("")node) differs from a node without tag (node). -
A node with empty children (e.g.
node {}) differs from a node without children (node). -
KDL does not differ between integer numbers and numbers with fractional part nor does it define a fixed limit to the length or precision of numbers.
-
property names differ also if their distinct strings become equivalent after Unicode normalization.
Applications must make clear whether they support full KDL data model or a specific subset and whether they modify KDL documents to fit to their limited model. Applications may further extend their document model with additional information such as line numbers beyond the scope of this specification.