Executable UML (xtUML or xUML) is both a software development method and a highly abstract software language. It was described for the first time in 2002 in the book "Executable UML: A Foundation for Model-Driven Architecture". The language "combines a subset of the UML (

Unified Modeling Language 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. UML provides a standard notation for many types of diagrams which can be roughly ...

) graphical notation with executable semantics and timing rules." The Executable UML method is the successor to the Shlaer–Mellor method. Executable UML models "can be run, tested, debugged, and measured for performance.", and can be compiled into a less abstract

programming language A programming language is a system of notation for writing computer programs. Programming languages are described in terms of their Syntax (programming languages), syntax (form) and semantics (computer science), semantics (meaning), usually def ...

to target a specific

implementation Implementation is the realization of an application, execution of a plan, idea, scientific modelling, model, design, specification, Standardization, standard, algorithm, policy, or the Management, administration or management of a process or Goal ...

. Executable UML supports model-driven architecture (MDA) through specification of platform-independent models, and the compilation of the platform-independent models into platform-specific models.

Overview

Executable UML is a higher level of

abstraction Abstraction is a process where general rules and concepts are derived from the use and classifying of specific examples, literal (reality, real or Abstract and concrete, concrete) signifiers, first principles, or other methods. "An abstraction" ...

than third-generation programming languages. This allows developers to develop at the level of abstraction of the application. The Executable UML aims for

separation of concerns In computer science, separation of concerns (sometimes abbreviated as SoC) is a design principle for separating a computer program into distinct sections. Each section addresses a separate '' concern'', a set of information that affects the code o ...

. This is supposed to increase ease of

reuse Reuse is the action or practice of using an item, whether for its original purpose (conventional reuse) or to fulfill a different function (creative reuse or repurposing). It should be distinguished from recycling, which is the breaking down of ...

and to lower the cost of

software development Software development is the process of designing and Implementation, implementing a software solution to Computer user satisfaction, satisfy a User (computing), user. The process is more encompassing than Computer programming, programming, wri ...

. This also enables Executable UML domains to be

cross-platform Within computing, cross-platform software (also called multi-platform software, platform-agnostic software, or platform-independent software) is computer software that is designed to work in several Computing platform, computing platforms. Some ...

. That means it is not tied to any specific programming language, platform or technology. Executable UML also allows for translation of platform-independent models (PIM) into platform-specific models (PSM). The Executable UML method enables valuing the model as

intellectual property Intellectual property (IP) is a category of property that includes intangible creations of the human intellect. There are many types of intellectual property, and some countries recognize more than others. The best-known types are patents, co ...

, since the model is a fully executable solution for the problem space. Actions are specified in action language. This means that the automatic generation of implementation code from Executable UML models can be output in an optimized form. Executable UML is intended to serve as executable code as well as documentation. The models are a graphical, executable specification of the problem space that is compiled into a target

. They are also intended to be human-readable.

Executable UML building blocks

system A system is a group of interacting or interrelated elements that act according to a set of rules to form a unified whole. A system, surrounded and influenced by its open system (systems theory), environment, is described by its boundaries, str ...

is composed of multiple subject matters, known as ''domains'' in Executable UML terms. Executable UML is used to model a domain at the level of

of its subject matter independent of implementation concerns. The resulting domain model is represented by the following elements: * The ''domain chart'' provides a view of the domain being modeled, and the dependencies it has on other domains. * The ''class diagram'' defines the

class Class, Classes, or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used d ...

es and class associations for the domain. * The ''statechart diagram'' defines the states, events, and state transitions for a class or class instance. * The ''action language'' defines the actions or operations that perform processing on model elements.

Domain chart

Executable UML requires identification of the domains (also known as: aspects or concerns) of the system. "Each domain is an autonomous world inhabited by conceptual entities" Each domain can be modeled independent of the other domains in the system, enabling a

. As an example, domains for an automated teller system may include the following: * The application domain model of the automated teller's

business logic In computer software, business logic or domain logic is the part of the program that encodes the real-world business rules that determine how data can be created, stored, and changed. It is contrasted with the remainder of the software that might ...

. * The security domain model of various issues regarding system security (such as

authentication Authentication (from ''authentikos'', "real, genuine", from αὐθέντης ''authentes'', "author") is the act of proving an Logical assertion, assertion, such as the Digital identity, identity of a computer system user. In contrast with iden ...

and

encryption In Cryptography law, cryptography, encryption (more specifically, Code, encoding) is the process of transforming information in a way that, ideally, only authorized parties can decode. This process converts the original representation of the inf ...

). * The data access domain model of methods for external

data Data ( , ) are a collection of discrete or continuous values that convey information, describing the quantity, quality, fact, statistics, other basic units of meaning, or simply sequences of symbols that may be further interpreted for ...

usage. * The

logging Logging is the process of cutting, processing, and moving trees to a location for transport. It may include skidder, skidding, on-site processing, and loading of trees or trunk (botany), logs onto logging truck, trucksuser interface In the industrial design field of human–computer interaction, a user interface (UI) is the space where interactions between humans and machines occur. The goal of this interaction is to allow effective operation and control of the machine fro ...

domain model of the user interactions with the system. * The

architecture Architecture is the art and technique of designing and building, as distinguished from the skills associated with construction. It is both the process and the product of sketching, conceiving, planning, designing, and construction, constructi ...

domain model of the implemented of the Executable UML model on the system's hardware and

software Software consists of computer programs that instruct the Execution (computing), execution of a computer. Software also includes design documents and specifications. The history of software is closely tied to the development of digital comput ...

platforms. The ''separation of concerns'' enables each domain to be developed and verified independently of the other domains in the system by the respective domain experts. The connections between domains are called ''bridges''. "A bridge is a layering dependency between domains". This means that the domains can place requirements upon other domains. It is recommended that bridges are agreed upon by the different domain experts. A domain can be marked as ''realized'' to indicate that the domain exists and does not need to be modeled. For example, a data access domain that uses a

MySQL MySQL () is an Open-source software, open-source relational database management system (RDBMS). Its name is a combination of "My", the name of co-founder Michael Widenius's daughter My, and "SQL", the acronym for Structured Query Language. A rel ...

database would be marked as realized.

Class diagram

Conceptual entities, such as tangible things, roles, incidents, interactions, and specifications, specific to the domain being modeled are abstracted into ''classes''. Classes can have ''attributes'' and ''operations''. The relationships between these classes will be indicated with ''associations'' and ''generalizations''. An association may require further abstraction as an ''Association Class''. Constraints on the class diagram can be written in both Action Language and Object Constraint Language (OCL). The Executable UML method limits the UML elements that can be used in an Executable UML class diagram. An Executable UML class diagram is meant to expose information about the domain. Too much complexity in the statechart diagrams is a good indicator that the class diagram should be reworked.

Statechart diagram

Classes have lifecycles which are modeled in Executable UML with a statechart diagram. The statechart diagram defines the ''states'', ''transitions'', ''events'', and ''procedures'' that define a class' behaviour. Each state has only one procedure that is executed upon entry into that state. A procedure is composed of actions, which are specified in an action language.

Action language

The class and state models by themselves can only provide a static view of the domain. In order to have an executable model, there must be a way to create class instances, establish associations, perform operations on attributes, call state events, etc. In Executable UML, this is done using an action language that conforms to the UML Action Semantics. Action Semantics was added to the UML specification in 2001. The Action Semantics RFP was based on previous work in action languages supporting the Shlaer–Mellor method. Existing action languages are Object Action Language (OAL), Shlaer–Mellor Action Language (SMALL), Action Specification Language (ASL), Model Action Specification Language (MASL), That Action Language (TALL), Starr's Concise Relational Action Language (SCRALL), Platform-independent Action Language (PAL) and PathMATE Action Language (PAL). SCRALL is the only one that is a graphical action language.

Model testing and execution

Once a domain is modeled, it can be tested independent of the target

by executing the model. Each domain can be verified and validated independent of any other domain. This allows

error An error (from the Latin , meaning 'to wander'Oxford English Dictionary, s.v. “error (n.), Etymology,” September 2023, .) is an inaccurate or incorrect action, thought, or judgement. In statistics, "error" refers to the difference between t ...

s detected to be associated with the domain and independent of other system concerns. Verification will involve such things as human

review A review is an evaluation of a publication, product, service, or company or a critical take on current affairs in literature, politics or culture. In addition to a critical evaluation, the review's author may assign the work a content rating, ...

of the models, performed by experts in the relevant domain, and automated checking of the Executable UML semantics. i.e., checking that the Executable UML model complies with the Executable UML metamodel. Validation will typically involve use of an Executable UML tool to execute the model. The execution can occur either before or after model compilation.

Model compilation

In order to support execution on the target

, the domain model must be translated into a less abstract form. This translation process is called ''model compilation''. Most model

compiler In computing, a compiler is a computer program that Translator (computing), translates computer code written in one programming language (the ''source'' language) into another language (the ''target'' language). The name "compiler" is primaril ...

s target a known

, because this allows reuse of existing

technologies. Optimizing the domain models for target

reasons will reduce the level of

, adversely affect domain independence, and increase the cost of

. In executable UML,

optimization Mathematical optimization (alternatively spelled ''optimisation'') or mathematical programming is the selection of a best element, with regard to some criteria, from some set of available alternatives. It is generally divided into two subfiel ...

s are done by the model

either automatically or through ''marking''. Marking allows specific model elements to be targeted for specific lower-level

s, and allows for broader architectural decisions, such as specifying that collections of objects should be implemented as a doubly linked list. In MDA terms, the model

creates the PSM. The separation between the PIM and PSM in Executable UML disables the ability to round-trip engineer the model, and deters modifications to the PSM.

Executable UML key aspects

Executable UML defines execution semantics for a subset of the UML. Key aspects of the Executable UML subset include the following: * No support for implementation specific constructs, like aggregation and composition. * Generalizations are always notated as . * Associations between classes are ''always'' named, have verb phrases on both ends specifying the roles, and have multiplicity specified on both ends. * Multiplicities on association ends are restricted to 0..1 (zero to one), * (zero to many), 1 (exactly one), or 1..* (one to many). *

Data type In computer science and computer programming, a data type (or simply type) is a collection or grouping of data values, usually specified by a set of possible values, a set of allowed operations on these values, and/or a representation of these ...

s are restricted to the following core data types: boolean, string, integer, real, date, timestamp, and arbitrary_id, or one of the following domain-specific data types: numeric, string, enumerated, and composite. Domain-specific numeric and string data types can represent subsets of the core data types. The domain-specific composite data type is to always be treated as a single unit within the domain. e.g., a ''MailingAddress'' composite data type could be declared, but city information couldn't be extracted from it. * Constraints on the Executable UML models can either be represented as Object Constraint Language (OCL) or action language.

fUML and ALF

The

Object Management Group The Object Management Group (OMG®) is a computer industry Standards Development Organization (SDO), or Voluntary Consensus Standards Body (VCSB). OMG develops enterprise integration and modeling standards for a range of technologies. Busin ...

has standardized the Foundational UML (fUML), which was strongly influenced by Executable UML. Action Language for Foundational UML (ALF), is a standard action language specification by the

Publications

* Gerry Boyd (2003) "Executable UML: Diagrams for the Future." published at ''devx.com'', February 5, 2003. * Shayne Flint, and Clive Boughton (2003) "Executable/translatable UML and Systems Engineering." ''Practical Approaches for Complex Systems (SETE 2003)''. * Shayne Flint, Henry Gardner, and Clive Boughton (2004). "Executable/Translatable UML in computing education." ''Proceedings of the Sixth Australasian Conference on Computing Education-Volume 30''. Australian Computer Society, Inc. * * Chapter 1 online * ''Executable and Translatable UML'' * Stephen J. Mellor (2004), Introduction to Executable and Translatable UML * Stephen J. Mellor (2004), A Framework for Aspect-Oriented Modelling * *

References

External links

* http://executableumlbook.com The official web site for "Executable UML: A Foundation for Model-Driven Architecture". {{DEFAULTSORT:Executable Uml Unified Modeling Language