When you work with a knowledge system that comprises material belonging to different subjects, you will probably want to keep different subjects in different sections of the knowledge hierarchy in the Contents window. You will probably also often want to design your items differently for questions in literature and for items related to maths.

For that purpose, SuperMemo introduces the concept of a category. A category is a section of knowledge hierarchy in the Contents window used for keeping material related to a single subject. Items added to a given category may use their own template that determines the location of particular components, colors, fonts, size of images, number of sound components, etc.

A category is characterized by the following attributes:

* node name - the name of the category (e.g. Geography)

* default template - template used in creating new items within the category

* root node - an element which is an ascendant of all elements included in the current category. By default, title of the root node element is used as the name of the category (e.g. Geography)

* hook node - a descendant of a root node to which Ctrl+A adds new items by default. Once the number of children of the hook node passes a defined limit, a new hook node is chosen (by the user or automatically). By definition, the new hook will naturally be a descendant of the root node.

Tools : Categories can be helpful in managing a large number of categories. Individual attributes of a given category can be changed. Name can be changed by typing in a new value. Default template can be changed by typing in the new name or by double clicking the template field and selecting a new template from the template registry. New root or hook nodes can be typed in or selected from among items included in the text registry (including the titles). Note that it is more convenient to determine root and hook nodes by options on the Contents menu.

The buttons at the bottom of the Categories window have the following functions:

* Add - add a new category

* Delete - delete the currently selected category

* Link - link a new value to the currently selected field in the current category

* OK - save the changes in categories file APPNODES.DAT in INFO subdirectory

* Cancel - cancel the changes to categories

* Help - display this page of help file

Tools : Categories is most useful to (1) delete categories, (2) change category templates, and (3) change category names.

To create a new category, you will most likely want to use Create category on the pop-up menu in the Contents window. Also to determine the root and hook you will rather use Make hook and Make root on the same menu.

Here is the typical way of working with categories:

1. Select a hierarchy node in the Contents window (this node will became the root and hook of the newly created category).

2. Choose Create category

3. To change the append template use Tools : Options : Appending : Default Item Template or Tools : Categories : Default Template

4. To change a category to another one, choose the new category in the combo box on the toolbar (under the timer)

Once you understand the concept of category, it will become very easy to manage a large number of items belonging to entirely different areas of knowledge.