can we use xml as database

Using xml as a database is ok for less data and no concern on the security of the data... for large datas its better to go with the relational database instead of xml. which provides more options compared to xml

The important point is no security. No central management of the user's credentials. File can easily corrupted. Files are easily readable to others. You need to encrypt decrypt every time. I recommended not to use xml as database.

yes