- xtUML and its Papyrus-xtUML (BridgePoint) tooling have advanced further in the last two years than in the ten preceding years. Acceleration in usage and improvements in tooling have been fueled by the open source software (OSS) ecosystems of Apache, Eclipse and Papyrus. Development teams have transformed from licensed users into user-contributors.
Keywords— xtUML, Shlaer-Mellor, Executable UML, UMLRT, MASL
Executable Translatable Unified Modeling Language
(xtUML) [
Shlaer-Mellor xtUML has enjoyed evolution and maturity while remaining true to the original method. The history, status and comparison to other dialects are outlined. The future of xtUML is predicted in light of the current players and the positive network effects of Eclipse, Papyrus and the open source community.
It is observed that a fully open source governance and ecosystem around xtUML has dramatically increased the pace of advancements in the tooling and facilitated collaboration among users, suppliers and academics. This is because openness, transparency and elimination of exclusive ownership fosters an environment of security. There is no single entity (licensing company) that must be trusted to serve the interests of all parties. Users can add features (or pay suppliers to add features) at will. In the xtUML community, features and fixes are being delivered faster than ever before. Related executable modeling languages and technologies are sharing in these improvements.
The Shlaer-Mellor xtUML method steps modelers through a sequence of abstract modeling constructs addressing data, control and processing views of systems applications. Data is modeled using class diagrams, control is modeled as state machines and processing is modeled with action language.
The order of modeling encourages as much information as reasonable to be captured in data with the exposure of abstractions at the highest possible level. The method is considered object-oriented due to its emphasis on data modeling. This object concept emphasizes relations between the data abstractions. UML class diagrams provide the notational richness required to capture clear abstractions of conceptual entities with classes, attributes and various forms of associations relating them. See Figure 1 for an example class diagram depicting the relationship between a dog and its owner. UML state machine diagrams (Figure 2) formalize the lifecycles of individual UML classes. The example illustrates the states of a test case. Thus, concurrent sequential processing is captured in a plurality of relatively simple, communicating instance-based state machines. Finally, activity semantics are modeled in class operations, state machine states and transitions, and function bodies using an abstract action language that is Turing Complete but platform independent. Models are partitioned along subject matter boundaries and deployed as compositions using UML component diagrams (Figure 3). The example shows the functional partitioning of an electrochemical (EC) analyzer and an instrumentation test runner which can stimulate and measure its response.
xtUML models are interpretively executable following a set of rules. These rules enforce the semantics of the model artifacts and establish a basis to govern time, order and priority. Execution can be performed in simulations run by humans enforcing the rules or by an xtUML interpreter that automates the execution for model testing purposes.
A corrolary set of semantics governs the tranformation of xtUML from one representation into semantically equivalent forms represented in lower-level target deployment languages such as Ada, SPARK, Java, C, C++, MISRA-C, AUTOSAR, SystemC, VHDL, (IDL, DocBook, HTML). The process of translating xtUML into other forms is called model compilation and is performed by a model compiler. A model compiler is a refinement of code generation in its complete and strict mapping of the semantic rules of the language. A model compiler must guarantee adherence to semantics to preserve execution behavior between forms. Model compilers can translate only from a higher level of abstraction to a lower level (or the same level). Model compilers can insert additional platform-specific detail into the transformation output. ShlaerMellor xtUML model compilers translate PIMs (Platform Independent Models) to PSMs (Platform Specific Models). • • • • • • • •
1988, 1991 Shlaer-Mellor Method published by
Stephen Mellor and Sally Shlaer in [
Software is "eating the world" [
The establishment of open source software and transparent governance has triggered a massive influx of openly accessible models, tooling source code, documentation, research results, education materials and supporting experience results. These contributions are coming from Europe, Asia and North America. Communities spanning these continents are collaborating at ever increasing rates due to the network effects and accessibility.
IV. KEY PLAYERS
xtUML is driven by several factors. The tooling would
seem to be the obvious driver, but the user base and the
collection of intellectual property (IP) are producing the real
energy. IP accumulated over decades provides a base. The
pool of existing models is continually upgraded and expanded
as the language and technology evolve. The cache of existing
models is extended as applications gain features and heritage
functionality is reused in fresh contexts. Models are beginning
to be exchanged more openly in shared repositories
encouraging reuse and providing a starting point for new
modelers [
Following are key user teams that influence the language and tools of xtUML.
Saab [
Fuji-Xerox [
Ericsson [
Agencies within the United Kingdom have been active Shlaer-Mellor modelers for most of two decades. One group recently migrated models from a commercial proprietary UML tool to Papyrus-xtUML (BridgePoint) and contributed a C++ model compiler targeted at distributed POSIX. Additionally, a run-time model debugger was added to the open source repository of xtUML tools.
A group within Agilent [
xtUML and Papyrus-xtUML (BridgePoint) have been used
in curricula at the university and secondary school levels.
Examples include universities in Japan (Shinshu University,
Kyushu University), Croatia (University of Zagreb), Hungary
(Budapest University of Technology and Economics), Sweden
(Chalmers of Technology) and a high school in the United
States (Faith Christian) [
The current body of intellectual property encoded as
xtUML models is rich and growing. One company reports an
investment of four hundred years of engineering in applications
employing the methodology. A recent trend is that more
models are shared openly [
One xtUML model of particular interest that is openly shared is the model of Papyrus-xtUML (BridgePoint) itself. The tool is simply an extension of the xtUML metamodel. Editor, Execution and Translation functionality are xtUML application domains built on top of the "OOA of OOA". The whole is compiled with a Java model compiler and packaged as Eclipse plugins. Papyrus-xtUML (BridgePoint) is a modeling tool that models and compiles itself.
xtUML tooling leverages underlying infrastructure based
on Java and Eclipse. Work is ongoing to establish greater
commonality and standardization by deploying EMF [
MASL [26] is a human readable concrete textual syntax for a Shlaer-Mellor derived modeling language. MASL describes both structure (classes and state machines) as well as activities (action language) in one cohesive textual language. MASL can be used to express the full semantics of graphical models and has become part of xtUML.
B. Alf
Alf [
UML-RT [
UML-RT is supported on the Papyrus Platform and has paved the way for xtUML to adopt a similar tooling approach built on the UML2 compliant editing platform provided by Papyrus. Papyrus-RT and Papyrus-xtUML (BridgePoint) are being managed in the same project group within the Papyrus Industry Consortium and are sharing underlying tools technology.
Papyrus-xtUML (BridgePoint) has been an Eclipse
application since 2004. However, until 2013 the source code
for the tooling was proprietary. In 2014 all of the tooling
opened up and has been placed under governance of the
Eclipse Foundation [
Look to see the benefits of Eclipse Foundation governance and a growth of the committer and contributor base during the next months and years.
Papyrus provides an open source standardized UML2 editing platform supporting profiles. Several modeling dialects are basing their tooling on the Papyrus Platform. Papyrus supports editors for Information Modeling, SysML, UML-RT and other UML-related idioms. Papyrus-xtUML (BridgePoint) is moving onto the Papyrus Platform to leverage this commonality of underlying technology.
Action languages are model-aware, abstract, platform independent syntaxes for the specification of processing. Papyrus-xtUML (BridgePoint) supports OAL and recently MASL. Support for Alf is under study. Experiments have demonstrated its feasibility.
The next state for action language is proliferation and pluggability. OAL is established; MASL is joining. Interpretive execution of MASL is expected soon. Support of state machine -enabled Alf will follow.
By default the Eclipse Modeling Framework (EMF) persists data as metamodel instances encoded with XMI. Parallel efforts in various modeling projects are exploring concrete textual syntaxes for modeling languages including the structural elements. Such an approach serializes the inmemory metamodel into a human readable, understandable, parsable and editable language. This strategy has advantages for editability and configuration management (diff/merge). With the advent of MASL and Alf, Papyrus-xtUML (BridgePoint) is likely to adopt this approach.
Related to the human readable persistence described above is a hybrid approach to editing both graphics and text. Graphics are being recognized as a view into the semantics of the model. Therefore, graphical and textual expressions of the meaning of the models can co-exist. Papyrus-xtUML (BridgePoint) can automatically render graphics from textual models. Expect to see advances in model editing that support concurrent textual/graphical editing.
The xtUML type system expressed in the metamodel is
largely the same as the original Shlaer-Mellor. Advances
proposed by Darwen and Date [
Members of the xtUML community have been involved in
the creation and refinement of the Foundational Executable
UML (fUML) [
xtUML has remained fundamentally true to the underlying Shlaer-Mellor method through time and tooling evolution. A body of successful projects, models, teams and companies illustrates the strength of this approach to executable modeling. Recent commitments to open source licensing, governance and ecosystems are accelerating advances in the tooling and collaboration between users, suppliers and academics. Specifically, Papyrus and the Papyrus Industry Consortium are bringing together these interested parties in a manner similar to the convergence of technologies in Eclipse. xtUML and executable modeling are benefiting. A Foundation for with
Japanese language naming [26] MASL – Model Action Specification Language github.com/xtuml/bridgepoint/tree/master/src/org.xtuml.bp.doc/Referenc e/MASL