Transformation rules are generally intended to simplify the structure of the thesaurus by reducing the number of links between pairs of terms. This will often make graphic displays easier to understand.
To add a structure transformation rule, select the type of rule from the drop-down list under "Transformation", use the spin edits to set its three linktypes, and then click on the "Add" button.
There are currently two types of rules that can be defined: (1) "Delete link 3" and (2) "Make virtual node". Their effects are illustrated in the following diagrams.
Diagram 1a shows a structure before application of a "Delete link 3" rule, and diagram 1b shows the result after application of the rule. Diagram 2a shows a structure before application of a "Make virtual node" rule, and diagram 2b shows the result after application of the rule.
As illustrated in diagrams 2a, a "virtual" node is a term derived from terms linked to other terms. Generally, if you want to keep a virtual node, you will want to change the term to something else.
Assuming linktype 4 is BT, linktype 5 is NT, and linktype 6 is RT, common "Delete link 3" rules would be
| Link 1 | Link 2 | Link 3 | Result |
|---|---|---|---|
| 4 | 4 | 4 | Deletes indirect BT/NT links. |
| 4 | 5 | 6 | Deletes RT links between terms with a common broader term. |
| 5 | 6 | 6 | Deletes RT links between pairs of terms where one already has an RT link to a broader term of the other. |
| Link 1 | Link 2 | Link 3 | Result |
|---|---|---|---|
| 5 | 5 | 5 | Creates an intervening term when two or more terms share two or more narrower terms. |
For more explanation of thesaurus structure transformations, see
To delete a structure transformation rule, select it and click on the "Delete" button.
To check or uncheck a structure transformation rule, click on its checkbox or select it and press Spacebar.
When finished with the "Structure transformation" dialog, click on the "Close" button to return to the main window.