Unified Modeling Language


The Unified Modeling Language is a general-purpose, object-oriented, visual modeling language that provides a way to visualize the architecture and design of a system, like a blueprint. 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 in object-oriented programming, 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 the OOPSLA '95 Conference. Originally, Grady Booch and James Rumbaugh merged their models into a unified model. This was followed by Booch's company Rational 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. The Object Management Group 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. In 1997, UML was adopted as a standard by the Object Management Group and has been managed by this organization ever since. In 2005, UML was also published by the International Organization for Standardization and the International Electrotechnical Commission as the ISO/IEC 19501 standard. Since then the standard has been periodically revised to cover the latest revision of UML.
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.

Use

UML is primarily used for software development but also used outside elsewhere including business processes, system functions, database schemas, workflow in the legal systems, medical electronics, Health care systems, and hardware design.
UML is designed for use with many object-oriented software development methods, both today and for the methods when it was first developed – including OMT, Booch method, Objectory, and especially RUP, which it was originally intended to be used with when work began at Rational Software. Although originally intended for object-oriented design documentation, UML has been used effectively in other contexts such as modeling business process.
As UML is not inherently linked to a particular programming language, it can be used for modeling a system independent of language. Some UML tools generate source code from a UML model.

Elements

UML diagrams support visualizing system aspects like:
In addition to syntactical elements with well-defined semantics, UML diagrams also allow for free-form comments that explain aspects such as usage, constraints, and intents.

Sharing

UML models can be exchanged among UML tools via the XML Metadata Interchange format.

Cardinality notation

As with database Chen, Bachman, and ISO ER diagrams, class models are specified to use "look-across" cardinalities, even though several authors
prefer same-side or "look-here" for roles and both minimum and maximum cardinalities. Recent researchers
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
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."

Artifacts

An artifact
is the "specification of a physical piece of information that is used or produced by a software development process, or by deployment and operation of a system" including models, source code, scripts, executables, tables in database systems, development deliverables, a design documents, and email messages.
An artifact is the physical entity that is deployed to a
node. 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.

Metamodeling

The OMG developed a metamodeling architecture to define UML, called the Meta-Object Facility. 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.
The metamodel 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".

Diagrams

UML 2 defines many types of diagrams shown as a taxonomy in the image.

Structure diagrams

Structure diagrams emphasize the structure of the system using objects, classifiers, relationships, attributes and operations. They are used to document software 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
  • State machine diagram
  • Use case diagram Depicts of a user's interaction with a system

    Interaction diagrams

Interaction diagrams, a subset of behavior diagrams, emphasize the flow of control and data between components of a system.

Adoption

In 2013, UML had been marketed by OMG for many contexts, but aimed primarily at software development with limited success.
It has been treated, at times, as a design silver bullet, which leads to problems. UML misuse includes overuse and assuming that novices can design with it.
It is considered a large language, with many constructs. Some people feel that UML's size hinders learning and therefore uptake.
Visual Studio removed support for UML in 2016 due to lack of use.

History

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 image shows a timeline of the history of UML and other object-oriented modeling methods and notation.

Origin

Rational Software 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: Rumbaugh's object-modeling technique and Grady Booch's method. They were soon assisted in their efforts by Ivar Jacobson, the creator of the object-oriented software engineering method, who joined them at Rational in 1995.

UML 1.x

UML is originally based on the notations of the Booch method, the object-modeling technique, and object-oriented software engineering, which were integrated into a single language. UML was developed at Rational Software in 1994–1995, with further development led by them through 1996.
Under the technical leadership of Rumbaugh, Jacobson, and Booch, a consortium called the UML Partners was organized in 1996 to complete the Unified Modeling Language specification and propose it to the Object Management Group for standardization. The partnership also contained additional interested parties. 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.
After the first release, a task force was formed to improve the language, which released several minor revisions, 1.3, 1.4, and 1.5.
The standards it produced have been noted as being ambiguous and inconsistent.