Uniqueness Constraints

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Uniqueness constraints in UML
Standard identifiers (primary keys)

A uniqueness constraint (or key constraint) requires that a property’s value—or the value list of a list of properties in the case of a composite key constraint—is unique among all instances of the given object type.

Uniqueness constraints in UML

For instance, in a UML class diagram with the object type Book, we can define the isbn attribute to be unique (or a key) by appending the user-defined property modifier keyword key in curly braces to the attribute’s definition in the Book class rectangle. This is shown in the following diagram:

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Introduction

The Foundations of Web Apps

Javascript Fundamentals

Building a Minimal Web App with Plain JS in Seven Steps

Integrity Constraints and Data Validation

Constraint Validation in Plain JS

Enumerations

Enumeration Attributes in Plain JS

Reference Properties and Unidirectional Associations

Implementing Unidirectional Functional Associations

Implementing Unidirectional Non-Functional Associations

Bidirectional Associations

Implementing Bidirectional Associations

Subtyping and Inheritance

Subtyping with Plain JS

Conclusion

Uniqueness Constraints

Uniqueness constraints in UML