Unified Modeling Language

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The Unified Modeling Language (UML) is a general-purpose, developmental, modeling language in the field of software engineering that is intended to provide a standard way to visualize the design of a system. [1]


The creation of UML was originally motivated by the desire to standardize the disparate notational systems and approaches to software design. It was developed at Rational Software in 1994–1995, with further development led by them through 1996. [1]

In 1997, UML was adopted as a standard by the Object Management Group (OMG), and has been managed by this organization ever since. In 2005, UML was also published by the International Organization for Standardization (ISO) as an approved ISO standard. [2] Since then the standard has been periodically revised to cover the latest revision of UML. [3]


History of object-oriented methods and notation OO Modeling languages history.jpg
History of object-oriented methods and notation

Before UML 1.0

UML has been evolving since the second half of the 1990s and has its roots in the object-oriented programming methods developed in the late 1980s and early 1990s. The timeline (see image) shows the highlights of the history of object-oriented modeling methods and notation.

It is originally based on the notations of the Booch method, the object-modeling technique (OMT) and object-oriented software engineering (OOSE), which it has integrated into a single language. [4]

Rational Software Corporation hired James Rumbaugh from General Electric in 1994 and after that the company became the source for two of the most popular object-oriented modeling approaches of the day: [5] Rumbaugh's object-modeling technique (OMT) and Grady Booch's method. They were soon assisted in their efforts by Ivar Jacobson, the creator of the object-oriented software engineering (OOSE) method, who joined them at Rational in 1995. [1]

UML 1.x

Under the technical leadership of those three (Rumbaugh, Jacobson and Booch), a consortium called the UML Partners was organized in 1996 to complete the Unified Modeling Language (UML) specification, and propose it to the Object Management Group (OMG) for standardization. The partnership also contained additional interested parties (for example HP, DEC, IBM and Microsoft). The UML Partners' UML 1.0 draft was proposed to the OMG in January 1997 by the consortium. During the same month the UML Partners formed a group, designed to define the exact meaning of language constructs, chaired by Cris Kobryn and administered by Ed Eykholt, to finalize the specification and integrate it with other standardization efforts. The result of this work, UML 1.1, was submitted to the OMG in August 1997 and adopted by the OMG in November 1997. [1] [6]

After the first release a task force was formed [1] to improve the language, which released several minor revisions, 1.3, 1.4, and 1.5. [7]

The standards it produced (as well as the original standard) have been noted as being ambiguous and inconsistent. [8] [9]

Cardinality notation

As with database Chen, Bachman, and ISO ER diagrams, class models are specified to use "look-across" cardinalities, even though several authors (Merise, [10] Elmasri & Navathe [11] amongst others [12] ) prefer same-side or "look-here" for roles and both minimum and maximum cardinalities. Recent researchers (Feinerer, [13] Dullea et al. [14] ) have shown that the "look-across" technique used by UML and ER diagrams is less effective and less coherent when applied to n-ary relationships of order strictly greater than 2.

Feinerer says: "Problems arise if we operate under the look-across semantics as used for UML associations. Hartmann [15] investigates this situation and shows how and why different transformations fail.", and: "As we will see on the next few pages, the look-across interpretation introduces several difficulties which prevent the extension of simple mechanisms from binary to n-ary associations."


UML 2.0 major revision replaced version 1.5 in 2005, which was developed with an enlarged consortium to improve the language further to reflect new experience on usage of its features. [16]

Although UML 2.1 was never released as a formal specification, versions 2.1.1 and 2.1.2 appeared in 2007, followed by UML 2.2 in February 2009. UML 2.3 was formally released in May 2010. [17] UML 2.4.1 was formally released in August 2011. [17] UML 2.5 was released in October 2012 as an "In progress" version and was officially released in June 2015. [17] Formal version 2.5.1 was adopted in December 2017. [18]

There are four parts to the UML 2.x specification:

Until UML 2.4.1, the latest versions of these standards were: [19]

Since version 2.5, the UML Specification has been simplified (without Superstructure and Infrastructure), and the latest versions of these standards are now: [20]

It continues to be updated and improved by the revision task force, who resolve any issues with the language. [21]


UML offers a way to visualize a system's architectural blueprints in a diagram, including elements such as: [4]

Although originally intended for object-oriented design documentation, UML has been extended to a larger set of design documentation (as listed above), [22] and been found useful in many contexts. [23]

Software development methods

UML is not a development method by itself; [24] however, it was designed to be compatible with the leading object-oriented software development methods of its time, for example OMT, Booch method, Objectory and especially RUP that it was originally intended to be used with when work began at Rational Software.


It is important to distinguish between the UML model and the set of diagrams of a system. A diagram is a partial graphic representation of a system's model. The set of diagrams need not completely cover the model and deleting a diagram does not change the model. The model may also contain documentation that drives the model elements and diagrams (such as written use cases).

UML diagrams represent two different views of a system model: [25]

UML models can be exchanged among UML tools by using the XML Metadata Interchange (XMI) format.

In UML, one of the key tools for behavior modeling is the use-case model, caused by OOSE. Use cases are a way of specifying required usages of a system. Typically, they are used to capture the requirements of a system, that is, what a system is supposed to do. [26]


UML 2 has many types of diagrams, which are divided into two categories. [4] Some types represent structural information, and the rest represent general types of behavior, including a few that represent different aspects of interactions. These diagrams can be categorized hierarchically as shown in the following class diagram: [4]

Hierarchy of UML 2.2 Diagrams, shown as a class diagram UML diagrams overview.svg
Hierarchy of UML 2.2 Diagrams, shown as a class diagram

These diagrams may all contain comments or notes explaining usage, constraint, or intent.

Structure diagrams

Structure diagrams represents the static aspects of the system. It emphasize the things that must be present in the system being modeled. Since structure diagrams represent the structure, they are used extensively in documenting the software architecture of software systems. For example, the component diagram describes how a software system is split up into components and shows the dependencies among these components.

Behavior diagrams

Behavior diagrams represent the dynamic aspect of the system. It emphasize what must happen in the system being modeled. Since behavior diagrams illustrate the behavior of a system, they are used extensively to describe the functionality of software systems. As an example, the activity diagram describes the business and operational step-by-step activities of the components in a system.

Interaction diagrams

Interaction diagrams, a subset of behavior diagrams, emphasize the flow of control and data among the things in the system being modeled. For example, the sequence diagram shows how objects communicate with each other regarding a sequence of messages.


Illustration of the Meta-Object Facility M0-m3.png
Illustration of the Meta-Object Facility

The Object Management Group (OMG) has developed a metamodeling architecture to define the UML, called the Meta-Object Facility. [27] MOF is designed as a four-layered architecture, as shown in the image at right. It provides a meta-meta model at the top, called the M3 layer. This M3-model is the language used by Meta-Object Facility to build metamodels, called M2-models.

The most prominent example of a Layer 2 Meta-Object Facility model is the UML metamodel, which describes the UML itself. These M2-models describe elements of the M1-layer, and thus M1-models. These would be, for example, models written in UML. The last layer is the M0-layer or data layer. It is used to describe runtime instances of the system. [28]

The meta-model can be extended using a mechanism called stereotyping. This has been criticized as being insufficient/untenable by Brian Henderson-Sellers and Cesar Gonzalez-Perez in "Uses and Abuses of the Stereotype Mechanism in UML 1.x and 2.0". [29]


UML has been marketed for many contexts. [23] [30]

It has been treated, at times, as a design silver bullet, which leads to problems. UML misuse includes overuse (designing every part of the system with it, which is unnecessary) and assuming that novices can design with it. [31]

It is considered a large language, with many constructs. Some people (including Jacobson) feel that UML's size hinders learning (and therefore, using) it. [32]

See also

Related Research Articles

Booch method

The Booch method is a method for object-oriented software development. It is composed of an object modeling language, an iterative object-oriented development process, and a set of recommended practices.

Object-modeling language

An object-modeling language is a standardized set of symbols used to model a software system using an object-oriented framework. The symbols can be either informal or formal ranging from predefined graphical templates to formal object models defined by grammars and specifications.

The XML Metadata Interchange (XMI) is an Object Management Group (OMG) standard for exchanging metadata information via Extensible Markup Language (XML).

Meta-Object Facility

The Meta-Object Facility (MOF) is an Object Management Group (OMG) standard for model-driven engineering. Its purpose is to provide a type system for entities in the CORBA architecture and a set of interfaces through which those types can be created and manipulated. The official reference page may be found at OMG's website.

Object-modeling technique

The object-modeling technique (OMT) is an object modeling approach for software modeling and designing. It was developed around 1991 by Rumbaugh, Blaha, Premerlani, Eddy and Lorensen as a method to develop object-oriented systems and to support object-oriented programming. OMT describes object model or static structure of the system.

In software and systems engineering, a use case is a list of actions or event steps typically defining the interactions between a role and a system to achieve a goal. The actor can be a human or other external system. In systems engineering, use cases are used at a higher level than within software engineering, often representing missions or stakeholder goals. The detailed requirements may then be captured in the Systems Modeling Language (SysML) or as contractual statements.

Model-driven architecture (MDA) is a software design approach for the development of software systems. It provides a set of guidelines for the structuring of specifications, which are expressed as models. Model-driven architecture is a kind of domain engineering, and supports model-driven engineering of software systems. It was launched by the Object Management Group (OMG) in 2001.

The Object Constraint Language (OCL) is a declarative language describing rules applying to Unified Modeling Language (UML) models developed at IBM and is now part of the UML standard. Initially, OCL was merely a formal specification language extension for UML. OCL may now be used with any Meta-Object Facility (MOF) Object Management Group (OMG) meta-model, including UML. The Object Constraint Language is a precise text language that provides constraint and object query expressions on any MOF model or meta-model that cannot otherwise be expressed by diagrammatic notation. OCL is a key component of the new OMG standard recommendation for transforming models, the Queries/Views/Transformations (QVT) specification.

Grady Booch American software engineer

Grady Booch is an American software engineer, best known for developing the Unified Modeling Language (UML) with Ivar Jacobson and James Rumbaugh. He is recognized internationally for his innovative work in software architecture, software engineering, and collaborative development environments.

James E. Rumbaugh is an American computer scientist and object-oriented methodologist who is best known for his work in creating the Object Modeling Technique (OMT) and the Unified Modeling Language (UML).

Ivar Jacobson

Ivar Hjalmar Jacobson is a Swedish-American computer scientist and software engineer, known as major contributor to UML, Objectory, Rational Unified Process (RUP), aspect-oriented software development and Essence.


A metamodel or surrogate model is a model of a model, and metamodeling is the process of generating such metamodels. Thus metamodeling or meta-modeling is the analysis, construction and development of the frames, rules, constraints, models and theories applicable and useful for modeling a predefined class of problems. As its name implies, this concept applies the notions of meta- and modeling in software engineering and systems engineering. Metamodels are of many types and have diverse applications.

Object-oriented analysis and design (OOAD) is a technical approach for analyzing and designing an application, system, or business by applying object-oriented programming, as well as using visual modeling throughout the software development process to guide stakeholder communication and product quality.

Activity diagram

Activity diagrams are graphical representations of workflows of stepwise activities and actions with support for choice, iteration and concurrency. In the Unified Modeling Language, activity diagrams are intended to model both computational and organizational processes, as well as the data flows intersecting with the related activities. Although activity diagrams primarily show the overall flow of control, they can also include elements showing the flow of data between activities through one or more data stores.

UML Partners was a consortium of system integrators and vendors convened in 1996 to specify the Unified Modeling Language (UML). Initially the consortium was led by Grady Booch, Ivar Jacobson, and James Rumbaugh of Rational Software. The UML Partners' UML 1.0 specification draft was proposed to the Object Management Group (OMG) in January 1997. During the same month the UML Partners formed a Semantics Task Force, chaired by Cris Kobryn, to finalize the semantics of the specification and integrate it with other standardization efforts. The result of this work, UML 1.1, was submitted to the OMG in August 1997 and adopted by the OMG in November 1997.

Model-driven engineering (MDE) is a software development methodology that focuses on creating and exploiting domain models, which are conceptual models of all the topics related to a specific problem. Hence, it highlights and aims at abstract representations of the knowledge and activities that govern a particular application domain, rather than the computing concepts.

Systems Modeling Language

The Systems Modeling Language (SysML) is a general-purpose modeling language for systems engineering applications. It supports the specification, analysis, design, verification and validation of a broad range of systems and systems-of-systems.


MagicDraw is a visual UML, SysML, BPMN, and UPDM modeling tool with team collaboration support. Designed for business analysts, software analysts, programmers, and QA engineers, this dynamic and versatile development tool facilitates analysis and design of object oriented (OO) systems and databases. It provides the code engineering mechanism, as well as database schema modeling, DDL generation and reverse engineering facilities.

Knowledge Discovery Metamodel (KDM) is a publicly available specification from the Object Management Group (OMG). KDM is a common intermediate representation for existing software systems and their operating environments, that defines common metadata required for deep semantic integration of Application Lifecycle Management tools. KDM was designed as the OMG's foundation for software modernization, IT portfolio management and software assurance. KDM uses OMG's Meta-Object Facility to define an XMI interchange format between tools that work with existing software as well as an abstract interface (API) for the next-generation assurance and modernization tools. KDM standardizes existing approaches to knowledge discovery in software engineering artifacts, also known as software mining.

Applications of UML

UML is a modeling language used by software developers. UML can be used to develop diagrams and provide users (programmers) with ready-to-use, expressive modeling examples. Some UML tools generate program language code from UML. UML can be used for modeling a system independent of a platform language. UML is a graphical language for visualizing, specifying, constructing, and documenting information about software-intensive systems. UML gives a standard way to write a system model, covering conceptual ideas. With an understanding of modeling, the use and application of UML can make the software development process more efficient.


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Further reading