Object diagram
Encyclopedia
An object diagram in the Unified Modeling Language
(UML), is a diagram
that shows a complete or partial view of the structure of a modeled system
at a specific time.
An Object diagram focuses on some particular set
of object
instances and attributes
, and the links between the instances. A correlated
set of object diagrams provides insight into how an arbitrary view of a system is expected to evolve over time. Object diagrams are more concrete than class diagram
s, and are often used to provide examples, or act as test cases for the class diagrams. Only those aspects of a model that are of current interest need be shown on an object diagram.
) and instance name, as well as attributes and other structural features using slots. Each slot corresponds to a single attribute or feature, and may include a value for that entity.
The name on an instance specification optionally shows an instance name, a ':' separator, and optionally one or more classifier names separated by commas. The contents of slots, if any, are included below the names, in a separate attribute compartment.
A link is shown as a solid line, and represents an instance of an association
.
In the first UML object diagram on the right, the instance in the leftmost instance specification is named v1, has IndependentVariable as its classifier, plays the NMinus2 role within the FibonacciSystem, and has a slot for the val attribute with a value of 0. The second object is named v2, is of class IndependentVariable, plays the NMinus1 role, and has val = 1. The DependentVariable object is named v3, and plays the N role. The topmost instance, an anonymous instance specification, has FibonacciFunction as its classifier, and may have an instance name, a role, and slots, but these are not shown here. The diagram also includes three named links, shown as lines. Links are instances of an association.
In the second diagram, at a slightly later point in time, the IndependentVariable and DependentVariable objects are the same, but the slots for the val attribute have different values. The role names are not shown here.
In the last object diagram, a still later snapshot, the same three objects are involved. Their slots have different values. The instance and role names are not shown here.
, you will typically draw object diagrams using some other diagram type, such as on a class diagram
. An object instance may be called an instance specification or just an instance. A link between instances is generally referred to as a link. Other UML entities, such as an aggregation or composition
symbol (a diamond) may also appear on an object diagram.
Unified Modeling Language
Unified Modeling Language is a standardized general-purpose modeling language in the field of object-oriented software engineering. The standard is managed, and was created, by the Object Management Group...
(UML), is a diagram
Diagram
A diagram is a two-dimensional geometric symbolic representation of information according to some visualization technique. Sometimes, the technique uses a three-dimensional visualization which is then projected onto the two-dimensional surface...
that shows a complete or partial view of the structure of a modeled system
System
System is a set of interacting or interdependent components forming an integrated whole....
at a specific time.
An Object diagram focuses on some particular set
Set (computer science)
In computer science, a set is an abstract data structure that can store certain values, without any particular order, and no repeated values. It is a computer implementation of the mathematical concept of a finite set...
of object
Object (computer science)
In computer science, an object is any entity that can be manipulated by the commands of a programming language, such as a value, variable, function, or data structure...
instances and attributes
Attribute (computing)
In computing, an attribute is a specification that defines a property of an object, element, or file. It may also refer to or set the specific value for a given instance of such....
, and the links between the instances. A correlated
Correlation
In statistics, dependence refers to any statistical relationship between two random variables or two sets of data. Correlation refers to any of a broad class of statistical relationships involving dependence....
set of object diagrams provides insight into how an arbitrary view of a system is expected to evolve over time. Object diagrams are more concrete than class diagram
Class diagram
In software engineering, a class diagram in the Unified Modeling Language is a type of static structure diagram that describes the structure of a system by showing the system's classes, their attributes, operations , and the relationships among the classes.- Overview :The class diagram is the main...
s, and are often used to provide examples, or act as test cases for the class diagrams. Only those aspects of a model that are of current interest need be shown on an object diagram.
Instance specifications
Each object and link on an object diagram is represented by an InstanceSpecification. This can show an object's classifier (e.g. an abstract or concrete classClass (computer science)
In object-oriented programming, a class is a construct that is used as a blueprint to create instances of itself – referred to as class instances, class objects, instance objects or simply objects. A class defines constituent members which enable these class instances to have state and behavior...
) and instance name, as well as attributes and other structural features using slots. Each slot corresponds to a single attribute or feature, and may include a value for that entity.
The name on an instance specification optionally shows an instance name, a ':' separator, and optionally one or more classifier names separated by commas. The contents of slots, if any, are included below the names, in a separate attribute compartment.
A link is shown as a solid line, and represents an instance of an association
Association (object-oriented programming)
In object-oriented programming, association defines a relationship between classes of objects that allows one object instance to cause another to perform an action on its behalf...
.
Object diagram example
As an example, consider one possible way of modeling production of the Fibonacci sequence.In the first UML object diagram on the right, the instance in the leftmost instance specification is named v1, has IndependentVariable as its classifier, plays the NMinus2 role within the FibonacciSystem, and has a slot for the val attribute with a value of 0. The second object is named v2, is of class IndependentVariable, plays the NMinus1 role, and has val = 1. The DependentVariable object is named v3, and plays the N role. The topmost instance, an anonymous instance specification, has FibonacciFunction as its classifier, and may have an instance name, a role, and slots, but these are not shown here. The diagram also includes three named links, shown as lines. Links are instances of an association.
In the second diagram, at a slightly later point in time, the IndependentVariable and DependentVariable objects are the same, but the slots for the val attribute have different values. The role names are not shown here.
In the last object diagram, a still later snapshot, the same three objects are involved. Their slots have different values. The instance and role names are not shown here.
Usage
If you are using a UML modeling toolUML tool
A UML tool or UML modeling tool is a software application that supports some or all of the notation and semantics associated with the Unified Modeling Language , which is the industry standard general purpose modeling language for software engineering.UML tool is used broadly here to include...
, you will typically draw object diagrams using some other diagram type, such as on a class diagram
Class diagram
In software engineering, a class diagram in the Unified Modeling Language is a type of static structure diagram that describes the structure of a system by showing the system's classes, their attributes, operations , and the relationships among the classes.- Overview :The class diagram is the main...
. An object instance may be called an instance specification or just an instance. A link between instances is generally referred to as a link. Other UML entities, such as an aggregation or composition
Object composition
In computer science, object composition is a way to combine simple objects or data types into more complex ones...
symbol (a diamond) may also appear on an object diagram.
External links
- General information on UML including the official UML 2.0 specification. See especially the section on InstanceSpecification.
- The Expressive Power of Object Diagrams, an illustration from the real world