![]() ![]() This notation is also used as an adornment to the basic notation of an element to visualize parts of an element’s specification that have no graphical cue.įor example, some properties of associations (order and changeability) are rendered using constraint notation. If you want to specify your semantics more precisely, you can use the UML’s Object Constraint Language (OCL) as shown in the following class diagram:Ī constraint is rendered as a string enclosed by brackets and placed near the associated element. As I mentioned before, constraints may be written as free-form text. A constraint is a condition (a Boolean expression) that restricts the extension of the associated element beyond what is imposed by the other language constructs applied to that element.Ī constraint specifies conditions that must be held true for the model to be well-formed.A constraint extends the semantics of a UML building block, allowing you to add new rules or modify existing ones. A constraint is one of three UML’s extensibility mechanisms: Steretypes, Tagged Values and Constraints.This can be a formal expression (OCL) or a semiformal or human-language formulation. A constraint is either declared in the tool and repeatedly used in several diagrams or identified and applied as needed in a diagram, for example:Ĭertain kinds of constraints (such as an association xor constraint) are predefined in UML, others may be user-defined. A constraint is an expression that constrains the semantics of an element, and it must always be true, or in other words, it is a restriction on an element that limits the usage of the element. ![]()
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