A MaxDB database instance is used as a store for the WebDAV documents and their properties (WebDAV Properties). The metadata needed for the indexing of XML documents, such as XML index definitions, is also stored in the database.
The indexing service accesses this metadata, and uses it to determine the index values for the XML documents that you want to index. These index values are stored as WebDAV properties with the documents in the database instance.
For the synchronous indexing of documents, an internal indexing service is already available as part of the WebDAV Service. You can adapt this internal service to your requirements.
If you want to index XML documents asynchronously, then you must define at least one separate indexing service.