The class processes some of EclipseLink properties. The class may be used for any properties, but it only makes sense to use it in the following two cases: 1. There is a set of legal values defined either requiring translation (like CacheTypeProp); or not (like LoggingLevelProp). 2. Property is really a prefix from which the property obtained by appending entity or class name (like DescriptorCustomizerProp - it corresponds to "eclipselink.descriptor.customizer." prefix that allows to define properties like "eclipselink.descriptor.customizer.myPackage.MyClass"). EclipseLink properties and their values defined in org.eclipse.persistence.config package. To add a new property: Define a new property in PersistenceUnitProperties; Add a class containing property's values if required to config package (like CacheType); Alternatively values may be already defined elsewhere (like in LoggingLevelProp). Add an inner class to this class extending Prop corresponding to the new property (like CacheTypeProp); The first constructor parameter is property name; the second is default value; In constructor provide 2-dimensional value array in case the values should be translated (like CacheTypeProp); in case translation is not required provide a single-dimension array (like LoggingLevelProp). In inner class Prop static initializer addProp an instance of the new prop class (like addProp(new CacheTypeProp())).