Unbound Declarative Object

Description

The Unbound Declarative Object (UDO) is a data modeling concept standardized within 3GPP, primarily documented in TS 26.953. It provides a framework for defining data objects in a declarative way, meaning the structure and semantics of the data are described independently of how they are processed or transported. This abstraction allows UDOs to represent complex information—such as service descriptions, policy rules, or analytics data—in a consistent format that can be understood and manipulated by various network functions and external applications. The model is designed to be extensible, supporting nested structures and rich metadata, which makes it suitable for dynamic service environments where data schemas may evolve.

Architecturally, a UDO consists of a set of attributes and relationships defined using a schema language, which could be based on formats like JSON Schema or XML Schema. This schema dictates the valid properties, data types, and constraints for the object. In operation, UDO instances are created, read, updated, and deleted through APIs, often exposed by network functions such as the Network Exposure Function (NEF) or Application Functions (AFs). The 'unbound' aspect signifies that these objects are not inherently tied to a specific protocol binding or transport mechanism; they can be serialized into various formats (e.g., JSON, XML) and conveyed over different interfaces, promoting interoperability.

UDOs play a critical role in modern 3GPP architectures, particularly in service-based interfaces and for network exposure capabilities. They enable third-party applications to interact with the network using high-level, semantically rich data models rather than low-level protocol messages. For example, in edge computing scenarios, a UDO might describe an application context or a quality of service requirement, which the network can then interpret and act upon. By standardizing such object models, 3GPP reduces integration complexity and accelerates the development of new services, as developers can rely on a common data vocabulary. The specification also addresses lifecycle management, including versioning and validation, ensuring that UDOs remain robust as networks evolve toward greater automation and openness.

Purpose & Motivation

The Unbound Declarative Object was introduced to address the growing need for flexible and standardized data representation in 3GPP networks, especially with the rise of service-based architectures and network exposure. Prior approaches often relied on rigid, protocol-specific data formats that were tightly coupled to particular interfaces, making it difficult to share information across different network domains or with external applications. This limitation hindered innovation and increased the cost of integrating new services, as each integration required custom mappings and adaptations.

UDOs solve this by providing a declarative model that separates data semantics from transport details, enabling a more agile and interoperable ecosystem. They were motivated by trends like network slicing, edge computing, and open APIs, where diverse stakeholders—from network operators to application developers—need a common language to describe resources, policies, and service requirements. By adopting UDOs, 3GPP aims to facilitate automated network management, support dynamic service creation, and enhance the programmability of 5G and beyond networks. This aligns with broader industry movements toward model-driven engineering and intent-based networking, where high-level declarations are translated into network configurations without manual intervention.

Key Features

• Declarative data modeling independent of protocol bindings
• Support for extensible schemas with nested structures and metadata
• Serialization into multiple formats like JSON and XML
• Lifecycle management including versioning and validation
• Integration with service-based interfaces for network exposure
• Enables standardized data exchange for applications and network functions

Evolution Across Releases

Defining Specifications