TheUnified Modeling Language (UML) is a general-purpose, object-oriented, visualmodeling language that provides a way to visualize the architecture and design of a system, like ablueprint.[1][2] UML defines notation for many types of diagrams which focus on aspects such as behavior, interaction, and structure.
UML is both a formal metamodel and a collection of graphical templates. The metamodel defines the elements in an object-oriented model such as classes and properties. It is essentially the same thing as the metamodel inobject-oriented programming (OOP), however for OOP, the metamodel is primarily used at run time to dynamically inspect and modify an application object model. The UML metamodel provides a mathematical, formal foundation for the graphic views used in the modeling language to describe an emerging system.
UML was created in an attempt to define a standard language for object-oriented programming at theOOPSLA '95 Conference. Originally,Grady Booch andJames Rumbaugh merged their models into a unified model. This was followed by Booch's companyRational Software purchasing Ivar Jacobson's Objectory company and merging their model into the UML. At the time Rational and Objectory were two of the dominant players in the small world of independent vendors of object-oriented tools and methods.[3] TheObject Management Group (OMG) then took ownership of UML.
The creation of UML was motivated by the desire to standardize the disparate nature of notational systems and approaches to software design at the time.[4] In 1997, UML was adopted as a standard by theObject Management Group (OMG) and has been managed by this organization ever since. In 2005, UML was also published by theInternational Organization for Standardization (ISO) and theInternational Electrotechnical Commission (IEC) as theISO/IEC 19501 standard.[5] Since then the standard has been periodically revised to cover the latest revision of UML.[6]
Most developers do not use UML per se, but instead produce more informal diagrams, often hand-drawn. These diagrams, however, often include elements from UML.[7]: 536
UML is designed for use with many object-oriented software development methods; both today and for the methods when it was first developed includingOMT,Booch method,Objectory, and especially forRUP which it was originally intended to be used with when work began at Rational Software.[10] Although originally intended for object-oriented design documentation, UML has been used effectively in other contexts such as modeling business process.[11][12]
As UML is not inherently linked to a particularprogramming language, it can be used for modeling a system independent of language. SomeUML tools generatesource code from a UML model.[13]
Component diagram for specifying how components interface with other components
Deployment diagram for specifying how components are deployed and executed on computational nodes
In addition to syntactical (notational) elements with well-defined semantics, UML diagrams also allow for free-form comments (notes) that explain aspects such as usage, constraints, and intents.
As with database Chen, Bachman, and ISOER diagrams, class models are specified to use "look-across"cardinalities, even though several authors (Merise,[15]Elmasri & Navathe,[16]amongst others[17])prefer same-side or "look-here" for roles and both minimum and maximum cardinalities. Recent researchers (Feinerer[18]and Dullea et al.[19])have shown that the "look-across" technique used by UML and ER diagrams is less effective and less coherent when applied ton-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[20]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 ton-ary associations."
An artifact is the physical entity that is deployed to anode.[21] Other UML elements such as classes and components are first manifest into artifacts and instances of these artifacts are then deployed. Artifacts can be composed of other artifacts.
The OMG developed ametamodeling architecture to define UML, called theMeta-Object Facility (MOF).[22] 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 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.[23]
The metamodel can be extended using a mechanism calledstereotyping. This has been criticized as being insufficient/untenable byBrian Henderson-Sellers and Cesar Gonzalez-Perez in "Uses and Abuses of the Stereotype Mechanism in UML 1.x and 2.0".[24]
Structure diagrams emphasize the structure of the system – using objects, classifiers, relationships, attributes and operations. They are used to documentsoftware architecture.
Behavior diagrams emphasize the behavior of a system by showing collaborations among objects and changes to the internal states of objects. They are used to describe the functionality of a system.
Activity diagram – Describes the business and operational activities of components
In 2013, UML had been marketed by OMG for many contexts, but aimed primarily at software development with limited success.[12][27]
It has been treated, at times, as a designsilver 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.[28]
It is considered a large language, with manyconstructs. Some people (includingJacobson) feel that UML's size hinders learning and therefore uptake.[29]
Visual Studio dropped support for UML in 2016 due to lack of use.[30]
According toGoogle Trends, use of the termUML has declined since 2004 although leveled off in the last 5 years.[31]
Timeline and relationships of object-oriented methods and notation
UML has evolved since the second half of the 1990s and has its roots in theobject-oriented programming methods developed in the late 1980s and early 1990s. The image shows a timeline of the history of UML and other object-oriented modeling methods and notation.
Rational Software hired James Rumbaugh fromGeneral Electric in 1994 and after that, the company became the source for two of the most popular object-oriented modeling approaches of the day:[32] Rumbaugh'sobject-modeling technique (OMT) and Grady Booch's method. They were soon assisted in their efforts byIvar Jacobson, the creator of theobject-oriented software engineering (OOSE) method, who joined them at Rational in 1995.[4]
Under the technical leadership of Rumbaugh, Jacobson, and Booch, a consortium called theUML Partners was organized in 1996 to complete theUnified Modeling Language (UML) specification and propose it to the Object Management Group (OMG) for standardization. The partnership also contained additional interested parties (for exampleHP,DEC,IBM, andMicrosoft). 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 byCris 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.[4][33]
After the first release, a task force was formed[4] to improve the language, which released several minor revisions, 1.3, 1.4, and 1.5.[34]
The standards it produced (as well as the original standard) have been noted as being ambiguous and inconsistent.[35]
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.[36]
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.[37] UML 2.4.1 was formally released in August 2011.[37] UML 2.5 was released in October 2012 as an "In progress" version and was officially released in June 2015.[37]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 UML Diagram Interchange that defines how UML 2 diagram layouts are exchanged
Until UML 2.4.1, the latest versions of these standards were:[38]
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:[39]
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.[40]
^abUnified Modeling Language 2.5.1. Object Management Group Document Number formal/2017-12-05. Object Management Group Standards Development Organization. December 2017.
^[1412.2458] Systems, Views and Models of UML. By Ruth Breu Radu Grosu Franz Huber Bernhard Rumpe Wolfgang Schwerin. arXiv arxiv.org
^Hubert Tardieu, Arnold Rochfeld and René Colletti La methode MERISE: Principes et outils (Paperback - 1983)
^Elmasri, Ramez, B. Shamkant, Navathe, Fundamentals of Database Systems, third ed., Addison-Wesley, Menlo Park, CA, USA, 2000.
^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.ISBN3540237232.
