Saving data in WPF application

You need to embrace separation of concerns. How can WPF be related to saving data? Data is one concern, UI is another one. And you really need to separate UI from other aspects of your programming system, as much as possible.

You can store data in many ways. First of all, with you minute volume of data, you can use a single file with serialization using XML, JSON or binary file for the media of your data. Please see:
http://en.wikipedia.org/wiki/Serialization[^],
http://msdn.microsoft.com/en-us/library/7ay27kt9%28v=vs.110%29.aspx[^].

In most cases, Data Contract is the best approach to serialization:
http://msdn.microsoft.com/en-us/library/ms733127%28v=vs.110%29.aspx[^],
http://msdn.microsoft.com/en-us/library/system.runtime.serialization.datacontractserializer%28v=vs.110%29.aspx[^],
http://msdn.microsoft.com/en-us/library/system.runtime.serialization.json.datacontractjsonserializer%28v=vs.110%29.aspx[^].

Please see my past answers where I advocate this approach:
How can I utilize XML File streamwriter and reader in my form application?[^],
Creating property files...[^],
deseralize a json string array[^].

For a database, review these options:
http://en.wikipedia.org/wiki/Comparison_of_relational_database_management_systems[^],
http://en.wikipedia.org/wiki/Comparison_of_object-relational_database_management_systems[^].

Your choice depends on many factors, including costs, maintenance, and your own taste.

—SA