The meta schema is a set of schema objects that describe the objects in the SmartPlant schema. The schema, on the other hand, is a set of schema objects that describe data objects.
The meta schema provides the building blocks upon which the SmartPlant schema is built. The classes in the meta schema do not directly describe data that is part of the schema. Instead, these classes describe the classes in the schema.
In the following UML diagram, for example, ClassDef is the meta schema object that describes the Pump object in the schema. The Pump class in the schema is an instance of ClassDef in the meta schema. The Pump class in the schema describes P-100, which is the data. P-100 is an instance of the Pump class.
All classes in the schema are instances of the ClassDef class in the meta schema. Similarly, all relationship definitions in the schema are of class RelDef, which is part of the meta schema.
The meta schema also describes itself. For example, all classes in the meta schema are also of the class ClassDef, which is defined as part of the meta schema.
Viewing the meta schema without a schema or data is useful if you want to understand the classes that the meta schema contains.
When you open the Schema Editor, the meta schema is already available for viewing before you open any other files. The meta schema is not stored in an external file and is always available in the Schema Editor.