Each relational database system has its own mechanisms for storing metadata. PDF files can contain two types of metadata. For an example of database-specific metadata access methods, see Oracle metadata. ExifTool implements its own open metadata format. The MP3 standard did not include a method for storing file metadata. The VTOC stores all metadata for the file. The file browser shows photo thumbnails along with a caption of the shooting information metadata. The default ratio of data to metadata block groups is 1&colon;2. This is useful in providing additional metadata and semantics to relationships of the nodes. Information about what metadata, or tagging, formats the players understand. Preceding and following the image are lines and pixels containing metadata and synchronization information. This currently includes images and metadata definitions. Acquisitions/Collection Development, Cataloging/Metadata, and Collection Preservation. XKeyscore has been integrated with MARINA, which is NSA's database for internet metadata. The Music Library, one of the Kodi metadata databases, is another key feature of Kodi.