In what format are database stored in deployed applications. For example microsoft access, do you specify in the requirements that the user install access or is there a general format that database can be stored

Well database are stored in various formats depending on the OS platform, let's say your database was written with VB(windows app), then your user must have mysql installed for the db application to be able to take in info. from the front end and store in the back end of the application. For the other types of db extensions, visit the link below to learn more.
http://www.file-extensions.org/filetype/extension/name/database-files

this is not what i am talking about, i have an extensive knowledge of sql server and the lot. What i just noticed is that in most applications, the database is usually not in a system recognized format which means that neither Microsoft Access nor sql server is being used (well maybe not directly). What i want to know is that is there a way the database format can be changed such that it is not viewable by the client.