XMLFileDataService data service is designed to work with the database in XML format. For correct operation of the service data required by the XSD schema of the database and the XML database file. You can get them using XMLSchemaGenerator (extension module Flexberry Designer to generate the XSD schema of the database).
To work with data in XML format is used System.Data.DataSet support transactions and SQL queries. PstrfDataSet also supports referential integrity constraints. To work XMLFileDataService you must enable the referential integrity constraints. Enable referential integrity by enabling properties EnforceConstraints. XMLSchemaGenerator by default, this property adds to true`.
As the connection string specifies the path to XSD and XML files without specifying the extension (both files must have the same name).
For example, in the folder C:\DataBase\ are files base.xsd and base.xml, then the path will look like the following: C:\DataBase\base