Information model
In OPC UA, an information model is a set of type definitions and standard instances published in its own namespace, so that the same machine concept looks the same on every server implementing it. Part 5 defines the base model; companion specifications and vendor models layer on top of it.
Types plus a namespace plus a promise
An information model is not a document a server reads; it is nodes the server actually exposes. It consists of ObjectTypes, VariableTypes, DataTypes, ReferenceTypes and often some standard instances, all published under one namespace URI, with modelling rules stating what an instance must carry. The promise it makes to a client is that a browse path and a type name mean the same thing everywhere the namespace appears.
The base model in Part 5
Part 5 defines the model every server has: the folder skeleton, the Server object at i=2253 with NamespaceArray, ServerStatus, ServerCapabilities and ServerDiagnostics, the base type hierarchies, and the standard event types. That is the model you can rely on before you know anything else about a server, and reading it is the first thing any diagnostic session should do.
Three layers you will meet
Core UA is the base. On top sit the OPC Foundation companion specifications - DI, Machinery, MachineTool, PackML and the rest - each in its own namespace and often built on another. On top of those sits the vendor or integrator model: subtypes of standard types, plus the plant-specific instances. A well-built server keeps its own inventions in its own namespace and derives from standard types rather than reinventing them, which is what makes a generic client useful against it.
Reading a server's models before you browse
The NamespaceArray tells you which models are loaded, ServerProfileArray which profiles and facets are claimed, and the ServerCapabilities capability codes - DI, PACKML, AUTOID, CNC and the rest from the normative list - which companion specifications the server advertises. Those three reads take a second and tell you more about what a server can do than an hour of browsing.
Defined in: Part 5 - Information Model defines the base model and the Server object; Part 3 - Address Space Model defines the constructs models are built from.
Last verified 7 September 2026 against OPC UA 1.05.07. OPC UA Connect is an educational resource and is not affiliated with the OPC Foundation.