An ABOUT query is a query on a document theme. A document theme is a concept that is sufficiently developed in the text. For example, an ABOUT query on US politics might return documents containing information about US presidential elections and US foreign policy. Documents need not contain the exact phrase US politics to be returned.
During indexing, document themes are derived from the knowledge base, which is a hierarchical list of categories and concepts that represents a view of the world. Some examples of themes in the knowledge catalog are concrete concepts such as jazz music, football, or Nelson Mandela. Themes can also be abstract concepts such as happiness or honesty.
During indexing, the system can also identify and index document themes that are sufficiently developed in the document, but do not exist in the knowledge base.
You can augment the knowledge base to define concepts and terms specific to your industry or query application. When you do so, ABOUT queries are more precise for the added concepts.
ABOUT queries perform best when you create a theme component in your index. Theme components are created by default for English and French.
Querying Stopthemes
Oracle Text enables you to query on themes with the ABOUT operator. A stoptheme is a theme that is not to be indexed. You can add and remove stopthemes with the CTX_DDL package. You can add stopthemes after indexing with the ALTER INDEX statement.