Unified Modeling Language—abbreviated as UML—is a graphical language officially defined by Object Management Group (OMG) for visualizing, specifying, constructing, and documenting the artifacts of a software system [106]. An artifact in software development is an item created or collected during the development process (example of artifacts includes use cases, requirements, design, code, executable files, etc.). UML offers a standard way to write system’s blueprints, including conceptual things such as business processes and system functions as well as concrete things such as programming language statements, database schemas, and reusable software components [37]. Despite that UML is designed for specifying, visualizing, constructing, and documenting software systems, it is not restricted only for software modeling. UML has been used for modeling hardware, and is used for business process modeling, systems engineering modeling and representing organizational structure, among many other domains [125].
The first UML specification (version 1.1) was published by OMG at 1997. Since then there has been continuously ongoing work to improve both the language and its corresponding specification. Additionally, we should admit that UML versions 1.4.2 and 2.4.1 have been published under International Organization for Standardization (ISO) [44] and International Electronical Commission (IEC) [43] as a standard. In year 2005, the version 1.4.2 was published as ISO/IEC 19501:2005 [46]. Following in year 2012, the version 2.4.1 was published as ISO/IEC 19505-1 [47] and ISO/IEC 19505-2 [48]. You should ask—why there are two separate ISO/IEC standards for single UML version? The answer hides in fact that beginning with UML version 2.0 its specification was divided in two parts (i.e., two separate documents)—so-called Infrastructure and Superstructure. Accordingly, the ISO/IEC standard is based on this separation. But what a surprise—UML version 2.5 specification [79] again is a single document.
During the two major and a number of revision versions of UML, the definition of UML is evolving. UML version 2.4.1 specification [77,78][78][78] defines the language as follows: “UML is a visual language for specifying, constructing, and documenting the artifacts of systems. It is a general-purpose modeling language that can be used with all major object and component methods, and that can be applied to all application domains (e.g., health, finance, telecom, aerospace) and implementation platforms (e.g., J2EE, .NET).”
The UML originally was developed in middle of 1990s as a combination of previously competing object-oriented analysis and design approaches:•
Booch method by Booch [13],•
Object-Modeling Technique (OMT) by Rumbaugh, Blaha, Premerlani, Eddy, and Lorensen [105],•
Object-Oriented Software Engineering (OOSE)by Jacobson, Christerson, Jonsson, and Overgaard [49], and•
Other contributions to modeling complex systems, e.g., statecharts by Harel [41].
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