It does, here's a schema from an image I just saved with the latest version. Pretty simple.

  CREATE TABLE image_attributes ( name text, value blob);
  CREATE TABLE layers (id text, parent_id text, sequence integer, uti text, name text, data blob);
  CREATE TABLE layer_attributes ( id text, name text, value blob);

Also, document-based apps that use Apple's Core Data framework (kinda ORM) usually use SQLite files for storage.