The previous object represents an individual record of a data table. The previous object provides a convenient way of manipulating and displaying records in .view files and .data files.
The previous Object in .view Files
In a .view file which contains a data region, the properties of the previous object correspond to the fields displayed by the data region; the values of those properties correspond to the values of the previous record displayed by the data region. For example, in a .view file with a data region bound to the AddressBook data table, the previous object will have the properties record.FirstName, record.LastName, record.Email, etc; the values of these properties will depend, not the current record, but on the record previously displayed by the data region. (Note that the properties of the previous object are determined by the ws:field tags present in the .view file, not by the fields of the table bound to the view.)
Use DataWeb Substitution Syntax to display the values of the previous object within a .view file.
The previous Object in .data Files
You can use the previous object and the record object to validate or manipulate data before changes are made to a data table. Both the previous and record objects are passed to the data class associated with each data table before the data table is modified. For a detailed discussion see Working with Data Classes.