The fourth restriction is that updates and inserts through views are not permitted if the statement would modify columns that are derived from more than one object. Updates and inserts on more than one object at a time are never allowed.
However, SQL Server allows view modification statements. For example, you can modify one underlying object of a view that contains columns from more than one underlying object.
For example, if a view contains three columns from the titles table and two columns from the publishers table, you can do an update operation on the view that changes only the columns from titles or only the columns from publishers. However, you cannot do an update on the view that changes one column from titles and one column from publishers.