You can either use SQLite with SQLite-NET or SQL Server Compact Edition for an offline database.
Quick edit: here and here is a comparison of SQL Server CE vs SQLite.
Question
I have a problem with in choosing a database for desktop applications. The application will work offline, and require a relational database.
My first idea was to create a strong typed dataset and keeping data in xml. But this is not a safe option.
The second idea is to place the SQL Express on computer, but it will be a exhausting.
Which option should I use? Maybe you have other ideas?
Solution
You can either use SQLite with SQLite-NET or SQL Server Compact Edition for an offline database.
Quick edit: here and here is a comparison of SQL Server CE vs SQLite.
OTHER TIPS
You should use standard *.mdf in-file-database with EF using LINQ. Client won't need anything other than .NET installed on his machine.