Cayenne defines a simple yet powerful object-based expression language. Cayenne expressions are database independent and are used as query qualifiers and orderings and also to perform in-memory evaluation with DataObjects (and generally any kind of Java Beans). BNF of Cayenne expression language is described here.

Expressions are broadly divided into the following categories: object property expressions (also called "path expressions"), arithmetic operations, and conditional expressions. Cayenne contains a parser to build expressions from strings, and also features explicit expression API. Various ways of creating and using expressions are described later in this chapter.