Working With Class Hierarchies

Up to now, you have created all product classes at the same level. The classes exist in the system without a connection to each other.

However, you can set up a hierarchical structure for classes. This offers several advantages, which we will explore in this lesson.

A hierarchy that is set up carefully makes finding a suitable class, and therefore the object you are looking for, easier.

With hierarchies, you can:

• Create any number of levels and any number of classes on each level.
• Build the classes on one level, side by side, in the system, or embed them in a hierarchical structure.
• Create a simple cross-class search or for characteristic inheritance.

The following video introduces two scenarios for building a hierarchy.

To create a class hierarchy, you can either:

To create a class hierarchy, you can work with either the transactions shown in the previous video, or with the appropriate transaction for the class hierarchy. The second option gives you a graphical interface that you can use to create, change, or delete objects, as shown in the following video.

In a class hierarchy without inheritance, no characteristics are assigned to the superior classes, as the following image shows.

Only the classes on the bottom level of the hierarchy have characteristics that describe assigned objects.

In a class hierarchy with inheritance, the superior classes have characteristics, which are inherited by its subordinate classes.The image below shows an example.

To add a characteristic to all classes in a sub-tree of a hierarchy, you only need to enter it once, in the superior class, not for each individual class.

There is no difference between hierarchy classes and classes with objects assigned to them.

When you set up a class hierarchy, you can restrict the allowed values of a characteristic from one level of the hierarchy to the next. To do this, you use the value assignment screen in transactions "classes to superior classes" and "objects/classes to class" (CL22N and CL24N).

When you set up a class hierarchy, the single-value attribute maintained in characteristics is irrelevant.

Characteristic Length can be restricted on any level of the hierarchy to a certain range of allowed values. In subordinate classes, you only see the restricted allowed values.

The following video shows how to find objects inside the initial class of a hierarchy with a step by step reduction of characteristic values.

In the previous scenario, you restricted the characteristic values within the initial class.

But suppose you want to apply this scenario to a class hierarchy. Inside a hierarchy, you can cannot extend the characteristic values; you can only restrict them further.

The following video explains subordinate classes within class hierarchies.

You can set up a hierarchy network, where a class can have multiple superior classes. The image below shows an example.

You can use different search paths to find your class.

The value assignment screen shows the characteristics of all superior classes.

Rebuilding a normal class and its characteristics is easy. Rebuilding a class hierarchy is a bit more difficult. So you may want to remove a class from a hierarchy. To make this decision, consider what to do with:

• The classified objects.
• The characteristics of the class.

The following video presents some factors for making this decision.