There are more than one database managed by digiKam :
- Core database which host all albums, items, searches data. - Thumbnails database to host image thumbs with wavelets compression images. - Similarity database to host image finger-prints with computed Haar algorithms. - Face database to host face areas on images and face histograms used by faces recognition. For technical reasons, code is located in libs/facesengine/facedb.
collection/ Collections management interface. coredb/ Core database implementation based on Database Engine. dbjobs/ Database jobs manager. engine/ Low Level database engine common to all database interface. haar/ Haar fingerprint algorithms used by Fuzzy Search tool. history/ Item history algorithms. imgqsort/ Image Quality algorithms. item/ Item management interfaces. server/ Internal database server. similaritydb/ Similarity database implementation based on Database Engine tags/ Tags management and Face tags interface. thumbsdb/ Thumbnails database implementation based on Database Engine. utils/ High level implementation based on Core database interface plus widgets and dialogs.

The file Metadata manipulation Qt wrapper:
- containers : all metadata classes to group information by categories. - engine : the low level metadata extraction class based on Exiv2 API and managing : * C++ exception from this library. * All API call protected by a common mutex to fix non re-entrancy from Exiv2. * All Exiv2 API are only used in this area to not expose all digiKam core classes of API changes. - dmetadata : the high level metadata class, based on metadata engine, but not based on Exiv2 API. This class must be used everywhere in digiKam. - exiftool : class to wrap exiftool command line tool.