Add new term <Term Name="Constraint" Type="Validation.ConstraintType" AppliesTo="Property EntityType ComplexType"> <Annotation Term="Core.Description" String="Condition that the annotation target has to fulfill" /> </Term> <ComplexType Name="ConstraintType"> <Property Name="FailureMessage" Type="Edm.String" Nullable="true"> <Annotation Term="Core.IsLanguageDependent" /> </Property> <Property Name="Condition" Type="Edm.Boolean" Nullable="false"> <Annotation Term="Core.Description" String="Value MUST be a dynamic expression that evaluates to true if and only if the constraint is fulfilled" /> </Property> </ComplexType> Example: <Annotation Term="Validation.Constraint" Qualifier="Comparison"> <Record> <PropertyValue Property="FailureMessage" String="Start date cannot be after end date" /> <PropertyValue Property="Condition"> <Le> <Path>StartDate</Path> <Path>EndDate</Path> </Le> </PropertyValue> </Record> </Annotation>