The systematic thesaurus of the OPAC is a hierachical collection of all descriptors which are used to categorize entries of the database concerning topics, time and geography. You can browse the descriptors by using the systematic tree view or the alphabetic register or by doing a text search on all descriptors.
Descriptors with the folder symbol contain more detailed descriptors of subcategories, which can be displayed by clicking on the descriptor text. If the descriptor has no subcategories, it is marked with a page symbol, and there is no link.
The number next to the descriptor shows the counter of all database entries which are tagged with the descriptor. You can display all these entries by clicking on the number.
You can add a descriptor to the selection with the [+] symbol. If you do so, and then click on the number of another descriptor to show the related entries then only the intersection of both descriptors will be displayed. Selecting a descriptor with the [+] symbol also gives you the possibility to filter the results by using the query form.
NOTE: Not all entries of the Opac are tagged with thesaurus descriptors, so an additional search with the regular query form may deliver different results.