Copyright © 2013 Ivar Jacobson International SA. All rights reserved UML: Once More with Meaning University of Maryland Model-Based System Engineering Colloquium Ed Seidewitz 15 April 2013

UML Prehistory: Object-Oriented Analysis and Design OOAD orthodoxy (c. 1980s): Organize programs to model the basic concepts of the problem domain. Problem: Programming languages (even OOPLs) are not particularly good as problem domain modeling languages. –Too much of a program must focus on implementation details. –As the program grows, the “big picture” gets lost. Solution: Use a graphical modeling notation for analysis and design. –“Model the problem domain” during analysis. –“Model the solution” in problem domain terms during design. –Use the solution model as a “blueprint” for coding. Consequence: “Modeling” in the software community became drawing pictures, for problem domain representation and solution blueprinting. –Precise “meaning” was only to be found in the programs themselves.

Unified Modeling Language v1.x Unified Modeling Language (UML) intended to “unify” the various OOAD graphical modeling languages of the early 1990s – UML 0.9 by Booch, Rumbaugh and Jacobson (“3 amigos”) 1996 – UML 1.0 proposed by Rational 1997 – UML 1.1 adopted by Object Management Group (OMG) The intent of OMG standardization was primarily to allow syntactic interchange of models between tools.

Unified Modeling Language v2.x There was a hope to add semantic interoperability to the UML standard with UML – UML 2.0 Request for Information (RFI) 2000 – UML 2.0 Requests for Proposal (RFPs) 2003 – UML 2.0 Adopted 2005 – UML 2.0 Finalized 2011 – UML Latest formal version “However, the presence of numerous variation points in these semantics (and the fact that they are defined informally using natural language), make it impractical to define this as a formal compliance type, since the number of possible combinations is very large.” –UML Superstructure Specification, v2.0 – 2.4.1

Unified Modeling Language v2.5 The UML 2.5 specification document is reorganized to be “consumable” and to remove redundancy and correct inconsistencies. Primarily focused on semantics descriptions – Future Development of UML RFI 2009 – UML Specification Simplification RFP (UML 2.5) 2012 – UML 2.5 Adopted 2013 – UML 2.5 Finalized (planned) “A tool demonstrating semantic conformance provides a demonstrable way to interpret UML semantics, e.g., code generation, model execution, or semantic model analysis.” –UML 2.5 Specification, Semantic Conformance

Foundational UML (fUML) Foundational UML (fUML) is an executable subset of standard UML that can be used to define, in an operational style, the structural and behavioral semantics of systems – Action Semantics for the UML RFP 2003 – UML 1.5 with action semantics formalized 2003 – UML 2.0 adopted 2005 – Semantics of a Foundational Subset for Executable UML Models RFP 2008 – fUML 1.0 Beta (based on UML 2.2) 2010 – fUML 1.0 Formal (based on UML 2.3) 2012 – fUML 1.1 Beta (based on UML 2.4.1)

Composite Structure Semantics Complete Activity Model Semantics State Machine Semantics fUML Scope Non- Executable Model Semantics The semantics of fUML provide the foundation for formally specifying the (execution) semantics of the rest of UML. Some areas of UML (e.g., use case and requirements models) may not be best formalized based on an executable semantics foundation. Interaction Model Semantics Foundational Semantics fUML operational semantics are specified as an execution model written in fUML itself. Base Semantics The base semantics of the subset of fUML used in the execution model are specified using formal logic.

fUML Key Components Foundational UML Subset (fUML) – A computationally complete subset of the abstract syntax of UML (Version 2.4.1) –Kernel – Basic object-oriented capabilities –Common Behavior – General behavior and asynchronous communication –Activities – Activity modeling, including structured activities (but not including variables, exceptions, swimlanes, streaming or other “higher level” activity modeling) Execution Model – A model of the execution semantics of user models within the fUML subset Foundational Model Library –Primitive Types – Boolean, String, Integer, Unlimited Natural –Primitive Behaviors – Boolean, String and Arithmetic Functions –Basic Input/Output – Based on the concept of “Channels”

Action Language for fUML (Alf) The Action Language for Foundational UML (Alf) is a textual surface representation for UML modeling elements with the primary of acting as the surface notation for specifying executable (fUML) behaviors within an overall graphical UML model – Concrete Syntax for a UML Action Language RFP 2010 – Alf 1.0 Beta (based on UML 2.4 and fUML 1.0) 2013 – Alf Beta (based on UML and fUML 1.1)

Alf Key Components Concrete Syntax – A BNF specification of the legal textual syntax of the Alf language. Abstract Syntax – A MOF metamodel of the abstract syntax tree that is synthesized during parsing of an Alf text, with additional derived attributes and constraints that specify the static semantic analysis of that text. Semantics – The semantics of Alf are defined by mapping the Alf abstract syntax metamodel to the fUML abstract syntax metamodel. Standard Model Library –From the fUML Foundational Model Library Primitive Types (plus Natural and Bit String) Primitive Behaviors (plus Bit String Functions and Sequence Functions) Basic Input/Output –Collection Functions – Similar to OCL collection operations for sequences –Collection Classes – Set, Ordered Set, Bag, List, Queue, Deque, Map

Hybrid SUV Example: Operational States A state machine abstracts system behavior into a finite number of states. The system is modeled as having discrete transitions between the states. A transition may trigger further system behavior… …or system behavior may be dependent on the current state/

Using Alf to Define a State Machine Behavior

Hybrid SUV Example: “Accelerate” Activity An activity specifies behavior as the coordinated execution of a set of subordinate actions. An action in one activity may call another activity. Data and control flow between the various actions.

Hybrid SUV Example: “Provide Power” Activity Other actions provide various data and computational functions.

Using Alf to Specify an Action After a certain level of detail, it is much more convenient to use a textual rather than graphical notation (whether mathematical constraints or procedural action language.)

Using Alf to Define an Activity (1) The original Alf statements can then be preserved in a comment element stereotyped as a «TextualRepresentation». Alf statements in the body of an opaque action may be compiled into an activity.

Using Alf to Define an Activity (2) namespace ‘Hybrid SUV’; private import Alf::Library::IntegerFunctions::Min; activity ProportionPower( in battCond: Integer, in accelPosition: Integer, in speed: Integer, out eThrottle: Integer, out gThrottle: Integer, out transModeCmd: TransModeCommand) { { throttle = (accelPosition * battCond) / GetMaxBattLevel(); eThrottle = Min(throttle, GetMaxEThrottle()); gThrottle = Min(accelPosition - throttle, GetMaxGThrottle()); transModeCmd = new TransModeCommand(); transModeCmd.level = speed / GetTransModeConv(); }

The Goal: Automated Execution and Analysis

Hardware and software engineers develop components to satisfy the requirements. Test engineers develop the test environment to verify the requirements. The Goal: Model Based System Engineering System engineers analyze, simulate and validate the system design, and allocate requirements to components. Using standard- conforming modeling tools Using a standard- conforming model execution tools System engineers create the models Execution artifacts could include: System behavior, timing and statistics Execution artifacts could include: System behavior, timing and statistics Models can include both hardware and software components. Using standard-based model interchange

Implementations fUML Implementations –Open Source Reference Implementation (Academic Free License 3.0) –Cameo Simulation Toolkit for MagicDraw from NoMagic –Advanced Modeling | UML Simulation and Execution (AM|USE) by LieberLieber for Enterprise Architect from Sparx Systems Alf Implementations –Open Source Reference Implementation (GNU General Public License 3.0) –Alf for Papyrus Eclipse UML Tool (Ongoing)

Ongoing Work fUML Version 1.2 Alf Version 1.1 Precise Semantics of UML Composite Structures Additional “Precise Semantics” RFPs –State machines –Interactions –Complete activities/process modeling