Declarative Objectivity (DO) Language : Expressions : Source-Specifier Expressions
Source-Specifier Expressions
A source-specifier expression is used in certain clauses to indicate the source of a query, which is the sequence of objects on which the query operates.
   
Syntax 
source : className | (className 's') ;
Used In 
FROM Clause, UPDATE Statement, DELETE Statement 
Quick Look 
Query over objects of the Customer class:
FROM Customer WHERE lastName == 'Smith' RETURN address.postalCode;
Update objects of the Customer class:
UPDATE Customers where rewardPoints == 0 SET rewardPoints TO 1200 RETURN userId;
Delete objects of the FleetData.Vehicle cass.
DELETE FleetData.Vehicle WHERE retired == true;
Discussion 
A query source is the sequence of persistent objects that instantiate a schema class. This sequence can be further filtered using an optional WHERE Clause, so that the resulting sequence consists of qualified source objects (objects that satisfy a predicate).
You identify the schema class by its class name, which should include namespace qualification if needed to identify a unique class (for example, FleetData.Vehicle). The namespace separator may either be a dot “.” or a double colon “::”.
Alternative Syntax
For readability, an optional s can be appended to any class name, provided there is no ambiguity. For example, if the schema includes a Vehicle class (but no Vehicles class) in the FleetData namespace, the following DELETE statements are equivalent:
DELETE FleetData.Vehicle WHERE retired == true;
DELETE FleetData.Vehicles WHERE retired == true;