Class

The class of a type describes whether the type represents a simple data object (item), a complex data object (group), or whether is used to organize types (category). Define the class of the selected type by selecting the class from the drop-down list in the Value column.

Category

Categories organize types that have common properties. Each category has a set of item properties and a set of group properties. Subtypes of the category inherit these properties.

A category does not define data objects in detail and it does not represent data to be used in a map. You never map a category type, so a category type does have components. A category type may be a component of a partitioned group, after a component with the identifier attribute. A category cannot be a component of a non-partitioned group.

Item

The item type represents a simple data object that does not consist of any objects. An item does not have components.

Group

The group type represents a complex data object that consists of components.

To change a type's class, select the type and choose the desired class for the Class property in the Properties window.

If you change a type to an item, all the types in its subtree become items. If you change a type to a group, all the types in its subtree become groups. This is because the schema has a classification hierarchy and all the nested subtypes of an item must be items. Similarly, all the nested subtypes of a group must be groups.