The XPages runtime is part of IBM Lotus Domino and leverages the proven and mature capabilities Domino provides. Domino uses a document-oriented database called NSF (Notes Storage Facility) to manage semi-structured data like rich text and files. The data is stored as documents and views allow finding specific documents efficiently.
The document oriented database is a core part of the Domino architecture. Note that these two referenced PDF documents are old but still give a good overview of the fundamental concepts.
Documents have unique ids and further built in fields like the last author, last modified date, etc. and they have custom application specific fields. Documents can contain rich text which can be formatted text and images (MIME) or full file attachments. Documents can be queried via APIs and views. Lotus Domino also supports full text search for a full database as built in feature.
Deployment and Distribution
XPages applications can easily be deployed on Domino servers or a cluster of Domino servers using IBM Lotus Domino Administrator and more precisely the replication/synchronization mechanism built into IBM Lotus Domino. The replication mechanism supports bi-directional conflict detection and resolution in distributed environments.
XPages applications and the document oriented database can be secured in multiple ways. There is a so called ACL (access control list) which contains a list of users, groups and roles and their access rights. Security can furthermore be applied on document level via reader and author fields.