Data mining — Best combination of category maps

Intelligent Miner® distinguishes between a balanced and an unbalanced hierarchy. A balanced hierarchy contains relations that start and end on two consecutive levels. An unbalanced hierarchy contains relations that pass across a hierarchy level.

The following figure shows a taxonomy with an unbalanced hierarchy:

Figure 1. Taxonomy with an unbalanced hierarchy

          Level 0                  Level 1                    Level 2

        Orange Juice   |
                       >>          Beverages          |
        Beer           |                              |
                                                      |
                                                      >>          Food
                                                      |
        Fish                                          |
                                                      |
        Cheese                                        |

If your hierarchy is unbalanced, you must make sure that a relation that crosses hierarchy levels is in the same subset as the other relations that end or start at the crossed hierarchy levels.

Usually, a taxonomy is defined by a number of recursive and non-recursive categories. You must do the following tasks:

Breaking up the set of relations in your taxonomy into subsets
Describing these subsets by category maps of suitable types

Consider the following issues when you break up the set of relations into subsets:

The relations between two hierarchy levels must reside in the same subset.
In a taxonomy, you can use identical names for items and categories on different levels only in a subset that contains not more than two consecutive hierarchy levels.
You cannot comply with all restrictions if the part of your taxonomy that is unbalanced uses identical names on different levels.
After you have determined the suitable subsets for your taxonomy, you are ready to set up the category maps.
- If a subset contains more than two levels, use a recursive category map to describe the subset.
- If a subset contains only two hierarchy levels, use a non-recursive category map.

Creating category maps for the balanced hierarchy

You can divide the taxonomy that is shown below into the following subsets:

One subset holds the relations between hierarchy level 0 and 1
The other subset holds the relations between hierarchy level 1 and 2

In this example, you must not split the relations into two subsets because the relations comply with the restrictions.

Figure 2. A taxonomy with a balanced hierarchy

          Level 0                  Level 1                    Level 2

        Orange Juice   |
                       >>         Beverages          |
        Beer           |                             |
                                                     |
                                                     >>         Food
                                                     |
        Tomato         |                             |
                       |                             |
        Cabbage        >>         Vegetables         |
                       |
        Carrot         |

Creating category maps for the unbalanced hierarchy

You cannot break up the taxonomy that is shown in Figure 1 into subsets because the relation Fish => Food crosses the hierarchy level 1. Therefore, it must reside with the following relations in the same subset:

Orange Juice => Beverage
Beer => Beverages
Beverages => Food

The same applies to the relation Cheese => Food. Consequently, all the relations of that taxonomy must reside in a single set.

The following examples show the best combination of category maps in various situations:

Your taxonomy is balanced. The item names and the category names are unique.
Use a recursive category map that holds the complete set of relations.

You can also define several non-recursive category maps, one for each relation between two consecutive hierarchy levels.
Your taxonomy is unbalanced. The item names and the category names are unique.
Use a recursive category map that holds the complete set of relations.
Your taxonomy is balanced. The item names and the category names are ambiguous among the hierarchy levels.
You must use non-recursive category maps.
Your taxonomy is unbalanced. The item names and the category names are unique in the unbalanced parts of the taxonomy and ambiguous in the balanced parts of the taxonomy.
You must separate the unbalanced parts of the taxonomy from the balanced parts. Describe the unbalanced parts by recursive category maps and the balanced parts by non-recursive category maps.

You can define name mappings for your taxonomy. This is helpful if your taxonomy uses identical item names and category names on different levels or if categories use codes, for example, the code 7000 might be used for Beverage.

You must define a name mapping for each category map individually. The name mapping acts on all categories of the category map except for the items and categories at the lowest hierarchy level of the category map.

You must not define a name mapping for the lowest level of a category map because the name mapping of the preceding category map acts on the lowest level. The first category map that contains all relations starting from hierarchy level 0 does not have a preceding category map. In this case, the name mapping for the lowest level is defined by the name mapping of the item field.

You define taxonomies when defining the logical data specification.

Note: A taxonomy must be acyclic; that is, a category must be neither a direct member nor an indirect member of itself.