Digital objects stored in the dLibra system have many various properties (metadata) which describe those objects and are related to them. We call those properties metadata. They are classified into three types, by their nature:

• structural metadata – they define the way in which complex digital objects are organized,
• administrative metadata – they make it possible to manage an objects: access permissions, the digital format of the files of the object, and
• descriptive metadata – they describe the object so that it can be found or identified; they may contain information about, for example, the author or the title.