Relational databases allow the user to create relationships between tables while in document databases the basic idea is that documents are independent.
Most of the advantages of document databases come from the document-oriented modeling. In a document-oriented model, data objects are stored as documents; each document stores your data and enables you to update the data or delete it. Analogous to the relational approach, complex parts (separate document(s)) can be implemented in a document, which will refer to these parts by a unique identifier.
However, in the document-model it is also possible to add a part as a property or collection inside the document representing the owner. In this case, if the owner is removed, the part will be removed with it automatically.
This approach is called data denormalization, where the owner document contains the actual value of the referenced entity in addition (or instead) to the foreign key. Therefore, this approach may...