ICS 121: UML Built-In Constraints

UML built-in constraints allow you to express common logical constraints on a UML model.
Built-in constraints are just written as one word. In contrast, OCL constraints are defined in a language much like first-order predicate logic.
They are written inside braces after the affected element

abstract: Abstract classes are usually written with their names in italics, but you can also use {abstract} if you cannot use italics.
ordered: Normally all associations are considered to be unordered. Adding {ordered} at one end of an association means that the list of related objects is ordered. The ordering rule itself is not written.
bag: Normally all associations are sets, meaning that pair of objects only occurs once. Using {bag} means that the same pair can occur more than once.
query: indicates that an operation only reads data from an instance without modifying the instance.
read only: indicates an attribute has only a getX() operation, no setX().
frozen: indicates that an attribute is set exactly once at instance creation time. Like java "final" keyword.
complete: indicates that the subclasses shown are the only subclasses that will ever be allowed.
hierarchy: indicates that the instances form a Composite Pattern
dag: indicates that the instances form a DAG (directed acyclic graph)