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Unified Modeling Language

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The unified modeling language (UML) is a general-purpose visual modeling language that is intended to provide a standard way to visualize the design of a system.[1]

UML provides a standard notation for many types of diagrams which can be roughly divided into three main groups: behavior diagrams, interaction diagrams, and structure diagrams.

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.[2]

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) and the International Electrotechnical Commission (IEC) as the ISO/IEC 19501 standard.[3] Since then the standard has been periodically revised to cover the latest revision of UML.[4]

In software engineering, most practitioners do not use UML, but instead produce informal hand drawn diagrams; these diagrams, however, often include elements from UML.[5]: 536 


History of object-oriented methods and notation

Before UML 1.0[edit]

UML has evolved 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.[6]

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:[7] 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.[2]

UML 1.x[edit]

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.[2][8]

After the first release, a task force was formed[2] to improve the language, which released several minor revisions, 1.3, 1.4, and 1.5.[9]

The standards it produced (as well as the original standard) have been noted as being ambiguous and inconsistent.[10]

Cardinality notation[edit]

As with database Chen, Bachman, and ISO ER diagrams, class models are specified to use "look-across" cardinalities, even though several authors (Merise,[11] Elmasri & Navathe,[12] amongst others[13]) prefer same-side or "look-here" for roles and both minimum and maximum cardinalities. Recent researchers (Feinerer[14] and Dullea et al. [15]) 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[16] 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[edit]

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 experiences on the usage of its features.[17]

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.[18] UML 2.4.1 was formally released in August 2011.[18] UML 2.5 was released in October 2012 as an "In progress" version and was officially released in June 2015.[18] The formal version 2.5.1 was adopted in December 2017.[1]

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

  • The Superstructure that defines the notation and semantics for diagrams and their model elements
  • The Infrastructure that defines the core metamodel on which the Superstructure is based
  • The Object Constraint Language (OCL) for defining rules for model elements
  • The UML Diagram Interchange that defines how UML 2 diagram layouts are exchanged

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

  • UML Superstructure version 2.4.1
  • UML Infrastructure version 2.4.1
  • OCL version 2.3.1
  • UML Diagram Interchange version 1.0.

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

  • UML Specification 2.5.1
  • OCL version 2.4

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


An example of components in a travel reservation system

UML offers a way to visualize a system's architectural blueprints in a diagram, including elements such as:[6]

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

Software development methods[edit]

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 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.[6] 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:[6]

Hierarchy of UML 2.2 Diagrams, shown as a class diagram
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[edit]

Structure diagrams represent the static aspects of the system. It emphasizes 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[edit]

Behavior diagrams represent the dynamic aspect of the system. It emphasizes 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[edit]

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

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]


In 2013, UML had been marketed by OMG for many contexts, but aimed primarily at software development with limited success.[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]

MS Visual Studio dropped support for UML in 2016 due to lack of usage.[33]

According to Google Trends UML has been on a steady decline since 2004.[34]

See also[edit]


  1. ^ a b Unified Modeling Language 2.5.1. OMG Document Number formal/2017-12-05. Object Management Group Standards Development Organization (OMG SDO). December 2017.
  2. ^ a b c d Unified Modeling Language User Guide, The (2 ed.). Addison-Wesley. 2005. p. 496. ISBN 0321267974. See the sample content: look for history
  3. ^ "ISO/IEC 19501:2005 - Information technology - Open Distributed Processing - Unified Modeling Language (UML) Version 1.4.3". Iso.org. 1 April 2005. Retrieved 7 May 2015.
  4. ^ "ISO/IEC 19505-1:2012 - Information technology - Object Management Group Unified Modeling Language (OMG UML) - Part 1: Infrastructure". Iso.org. 20 April 2012. Retrieved 10 April 2014.
  5. ^ Sebastian Baltes; Stephan Diehl (11 November 2014). "Sketches and diagrams in practice". Proceedings of the 22nd ACM SIGSOFT International Symposium on Foundations of Software Engineering. FSE 2014. Association for Computing Machinery. pp. 530–541. arXiv:1706.09172. doi:10.1145/2635868.2635891. ISBN 978-1-4503-3056-5. S2CID 2436333.
  6. ^ a b c d "OMG Unified Modeling Language (OMG UML), Superstructure. Version 2.4.1". Object Management Group. Retrieved 9 April 2014.
  7. ^ Andreas Zendler (1997) Advanced Concepts, Life Cycle Models and Tools for Objeckt-Oriented Software Development. p. 122
  8. ^ "UML Specification version 1.1 (OMG document ad/97-08-11)". Omg.org. Retrieved 22 September 2011.
  9. ^ "UML". Omg.org. Retrieved 10 April 2014.
  10. ^ Génova et alia 2004 "Open Issues in Industrial Use Case Modeling"
  11. ^ Hubert Tardieu, Arnold Rochfeld and René Colletti La methode MERISE: Principes et outils (Paperback - 1983)
  12. ^ Elmasri, Ramez, B. Shamkant, Navathe, Fundamentals of Database Systems, third ed., Addison-Wesley, Menlo Park, CA, USA, 2000.
  13. ^ Paolo Atzeni; Wesley Chu; Hongjun Lu; Shuigeng Zhou; Tok Wang Ling, eds. (27 October 2004). Conceptual Modeling – ER 2004: 23rd International Conference on Conceptual Modeling, Shanghai, China, November 8–12, 2004. Lecture Notes in Computer Science 3288 (2004 ed.). Springer.
  14. ^ Ingo Feinerer (March 2007). A Formal Treatment of UML Class Diagrams as an Efficient Method for Configuration Management (PDF) (Doctor of Technical Sciences thesis). Vienna: Technical University of Vienna.
  15. ^ James Dullea; Il-Yeol Song; Ioanna Lamprou (1 November 2003). "An analysis of structural validity in entity-relationship modeling". Data & Knowledge Engineering. 47 (2): 167–205. doi:10.1016/S0169-023X(03)00049-1.
  16. ^ Sven Hartmann (17 January 2003). Reasoning about participation constraints and Chen's constraints. ADC '03: Proceedings of the 14th Australasian database conference. Australian Computer Society. pp. 105–113. Open access icon
  17. ^ "UML 2.0". Omg.org. Retrieved 22 September 2011.
  18. ^ a b c "UML". Omg.org. Retrieved 22 September 2011.
  19. ^ OMG. "OMG Formal Specifications (Modeling and Metadata paragraph)". Retrieved 12 February 2016.
  20. ^ OMG. "about the unified modeling language specification". Retrieved 22 February 2020.
  21. ^ "Issues for UML 2.6 Revision task Force mailing list". Omg.org. Retrieved 10 April 2014.
  22. ^ Satish Mishra (1997). "Visual Modeling & Unified Modeling Language (UML): Introduction to UML" Archived 20 July 2011 at the Wayback Machine. Rational Software Corporation. Accessed 9 November 2008.
  23. ^ a b "UML, Success Stories". Retrieved 9 April 2014.
  24. ^ John Hunt (2000). The Unified Process for Practitioners: Object-oriented Design, UML and Java. Springer, 2000. ISBN 1-85233-275-1. p. 5.door
  25. ^ Jon Holt Institution of Electrical Engineers (2004). UML for Systems Engineering: Watching the Wheels IET, 2004, ISBN 0-86341-354-4. p. 58
  26. ^ Manuel Almendros-Jiménez, Jesús & Iribarne, Luis. (2007). Describing Use-Case Relationships with Sequence Diagrams. Comput. J.. 50. 116-128. 10.1093/comjnl/bxl053.
  27. ^ Iman Poernomo (2006) "The Meta-Object Facility Typed Archived 30 June 2016 at the Wayback Machine" in: Proceeding SAC '06 Proceedings of the 2006 ACM symposium on Applied computing. pp. 1845–1849
  28. ^ "UML 2.4.1 Infrastructure". Omg.org. 5 August 2011. Retrieved 10 April 2014.
  29. ^ Brian Henderson-Sellers; Cesar Gonzalez-Perez (1 October 2006). "Uses and abuses of the stereotype mechanism in UML 1.x and 2.0". MoDELS '06: Proceedings of the 9th international conference on Model Driven Engineering Languages and Systems. Lecture Notes in Computer Science 4199. Berlin, Germany: Springer-Verlag: 16–26. doi:10.1007/11880240_2.
  30. ^ "UML 2.5: Do you even care?". "UML truly is ubiquitous"
  31. ^ "Death by UML Fever".
  32. ^ "Ivar Jacobson on UML, MDA, and the future of methodologies".
  33. ^ Krill, Paul (18 October 2016). "UML to be ejected from Microsoft Visual Studio". InfoWorld. Retrieved 23 July 2023.
  34. ^ "Google Trends". Google Trends. Archived from the original on 23 July 2023. Retrieved 23 July 2023.

Further reading[edit]

External links[edit]