Modelica_StateGraph2.UsersGuide

Library Modelica_StateGraph2 is a free Modelica package providing components to model discrete event and reactive systems in a convenient way. This package contains the User's Guide for the library and has the following content:

1. "Tutorial" gives an overview of the most important aspects of the StateGraph2 library.
2. "Comparison with StateGraph1" explains the significant enhancements with respect to the previous Modelica.StateGraph version.
3. "Release Notes" summarizes the differences between different versions of this library.
4. "Literature" provides references that have been used to design and implement this library.
5. "Used Modelica Extensions" summarizes the non-standard extensions used by this library.
6. "Modelica License 2" is the license under which this package and all of its subpackages is released.
7. "Contact" provides information about the authors of the library as well as acknowledgments.

Package Content

Name	Description
Tutorial	Tutorial
ComparisonWithStateGraph1	Comparison with StateGraph1
ReleaseNotes	Release notes
Literature	Literature
UsedModelicaExtensions	Used Modelica Extensions
ModelicaLicense2	Modelica License 2
Contact	Contact

Modelica_StateGraph2.UsersGuide.ComparisonWithStateGraph1

The Modelica_StateGraph2 library (called StateGraph2 below) is based on the experience with the current Modelica.StateGraph library (called StateGraph1 below) and is a significantly further development of StateGraph1. Furthermore, it is heavily based on the article (Malmheden et. al. 2008), see literature, but uses a different implementation technique as described in this article. The StateGraph2 library has the following improvements with respect to the StateGraph1 library:

• 3 Basic Components (Step, Transition, Parallel)
  All multiple versions of a component are combined in only one version (e.g., one step and not 4 step components). This is easier to understand and more convenient to use. The "Parallel" component is both used as "composite step" (so only one branch), as well as "parallel step" (so several execution branches).
   
• Conveniently connecting components
  Connecting components of a state machine in Modelica means to provide new vector dimensions and to provide a vector index to connect to. In StateGraph2, the new "connectorSizing" annotation is used and therefore all this is now performed automatically (from a users point of view, these actions are hidden; this is not the case in StateGraph1 and makes the usage of the StateGraph1 library clumsy).
   
• Safer state machines
  It is no longer possible to construct a wrong state machine in the sense that properties of the graph are violated (e.g. two initial steps, or branching wrongly out of a parallel component). Contrary to StateGraph2, in StateGraph1 such wrong graphs do not lead to an error but to unexpected simulation results. Still, other desirable properties of a state machine, such as "no deadlock" or "lifeliness" or "every step reachable", are not (yet) guaranteed with the current StateGraph2.
   
• Composite, autonomous, synchronized, preempted subgraphs
  Composite steps and parallel steps are described in a much better and more powerful way as in StateGraph1: Either by component "Parallel" or by inheriting from "PartialParallel". The first alternative has the advantage that it is simple to use (not necessary to construct a new class and instanciating this class, and easy variable access since no new hierarchy is constructed), the second alternative has the advantage that it introduces a Modelica hierarchy (useful for large subgraphs). In both cases, various options are possible, such as
  1. autonomous subgraphs (branches are executed in parallel autonomously),
  2. synchronized subgraphs (branches are executed in parallel and are synchronized before leaving the subgraph via the outPort),
  3. subgraphs with preemption and exception (a parallel step can be interrupted via the suspend ports and can continue execution via the resume ports).
  This is achieved by enabling/disabling the different ports.
   
• No infinite looping:
  As in StateGraph1, there are two types of transitions: immediate transitions (during event iteration all immediate transitions fire until no transition condition is true anymore) and delayed transitions (a transition fires only after a delay). Contrary to StateGraph1, in StateGraph2 every loop must have at least one delayed transition. If this is not the case a translation error occurs which states that the model contains an algebraic loop between Booleans with the name "checkOneDelayedTransitionPerLoop".
       This property guarantees that an event iteration over a StateGraph2 converges after a finite number of iterations, provided the modeller does not introduce an unsafe construct in the actions associated with a StateGraph2 (e.g. "i = pre(i) + 1" in the equation section outside of a when-clause will give an event iteration that never stops).
       It is possible to switch off this feature, by setting parameter "loopCheck = false" in one transition of a loop, instead of using a "delayed transition" at this place (in cases where immediate transitions are important and the transition conditions are in a form that they cannot fire at the same time instant).

Modelica_StateGraph2.UsersGuide.ReleaseNotes

Version 2.0.1, 2010-11-08

Uses Modelica Standard Library 3.2

Version 2.0, 2009-08-10

First version of the Modelica_StateGraph2 library based on Modelica.StateGraph and the prototype ModeGraph library from Martin Malmheden. The changes with respect to Modelica.StateGraph (version 1) are summarized here.

Modelica_StateGraph2.UsersGuide.Literature

The Modelica_StateGraph2 library is described in detail in (Otter et. al. 2009, see below) and is additionally based on the following references:

André, C. (2003):

Semantics of S.S.M (Safe State Machine).. I3S Laboratory, UMR 6070 University of Nice-Sophia Antipolis / CNRS.
 

Arzen K.-E. (2004):

JGrafchart User Manual. Version 1.5. Department of Automatic Control, Lund Institute of Technology, Lund, Sweden, Feb. 13, 2004.
 

Dressler I. (2004):

Code Generation From JGrafchart to Modelica.. Master thesis, supervisor: Karl-Erik Arzen, Department of Automatic Control, Lund Institute of Technology, Lund, Sweden, March 30, 2004.
 

Elmqvist H., Mattsson S.E., Otter M. (2001):

Object-Oriented and Hybrid Modeling in Modelica. Journal Europeen des systemes automatises (JESA), Volume 35 - n. 1, 2001.
 

Harel, D. (1987):

A Visual Formalism for Complex Systems. Science of Computer Programming 8, 231-274. Department of Applied Mathematics, The Weizmann Institute of Science, Rehovot, Israel.
 

Malmheden M. (2007):

ModeGraph - A Mode-Automata-Based Modelica Library for Embedded Control. Master thesis, Department of Automatic Control, Lund University, Sweden.
 

Malmheden M., Elmqvist H., Mattsson S.E., Henrisson D., Otter M. (2008):

ModeGraph - A Modelica Library for Embedded Control based on Mode-Automata. Modelica'2008 Conference, March 3-4, 2008.
 

Maraninchi F., Rémond, Y. (2002):

Mode-Automata: A New Domain-Specific Construct for the Development of Safe Critical Systems.
 

Mosterman P., Otter M., Elmqvist H. (1998):

Modeling Petri Nets as Local Constraint Equations for Hybrid Systems using Modelica. SCSC'98, Reno, Nevada, USA, Society for Computer Simulation International, pp. 314-319, 1998.
 

Otter M., Malmheden M., Elmqvist H., Mattsson S.E., Johnsson C. (2009):

A New Formalism for Modeling of Reactive and Hybrid Systems. Modelica'2009 Conference, Como, Italy, Sept. 20-22, 2009.

Modelica_StateGraph2.UsersGuide.UsedModelicaExtensions

This library is implemented with the Modelica 3.1 language. Additionally, some extensions to the Modelica language are used, in order to guarantee that only valid StateGraph2 graphs are accepted by a Modelica tool. It is planned to introduce these new language elements into the next version 3.2 of the Modelica language. This means, only Modelica tools will be able to process this Modelica_StateGraph2 package, if the following (non-standard) extensions of Modelica are supported:

Connection Graphs for State Diagrams (new section 9.4.2)

In order that a Modelica translator can guarantee the connection structure of hierarchical state diagrams, some additional operators are needed for the virtual connection graph. This special virtual connection graph is called "virtual state diagram graph" in the sequel. Virtual state diagram graphs are undirected graphs having overdetermined type or record instances as nodes. The branches are defined by connect(..) and by Connections.branch(..) statements. With the new operators Connections.uniqueRoot(..) and Connections.uniqueRootIndices(..) restrictions to the graph are introduced, as defined in the following table. If one node of a virtual connection graph is marked with uniqueRoot(..), then a virtual state diagram graph is present and it is not allowed to apply the operators Connections.root(..), Connections.potentialRoot, or Connections.isRoot(..) on a node of this graph.

• New operator: Connections.uniqueRoot(root, message="")
  The overdetermined type or record instance "root" is a unique root node in a virtual state diagram graph. Every virtual state diagram graph must have exactly one uniqueRoot(..) definition, before breakable branches are removed. Argument "root" may be a vector. Then, the operator is applied on every element of this vector. The second argument is a message that shall be reported if the root is not unique. From all uniqueRoot(..) definitions of the same graph, only one of the message arguments shall (arbitrarily) be selected and used in the error message. [The error message should additionally include the path (= instance names) between the unique root definitions. A typical value for message is: "Two or more state diagram graphs are connected that should not be connected"]
   
• New operator: rootIndices = Connections.uniqueRootIndices(roots, nodes, message="")
  The two first input arguments are vectors of overdetermined types or record instances with the restriction that size(nodes,1) ≤ size(roots,1). Vector "roots" must contain unique roots in the virtual state diagram graphs. The function returns an Integer vector which is a permuted version of vector "1:size(roots,1)":
  • rootIndices[i], i = 1,.., size(nodes,1):
    There is a path from roots[rootIndices[i]] to nodes[i]. It is an error, if such a path does not exist. In such a case, the error message should include the third argument "message".
  • rootIndices[j], j = size(nodes,1) + 1, ..., size(roots,1):
    There is no path from roots[rootIndices[j]] to an element of nodes[:].
  [The typical use is to verify the connection structure of a Parallel component. Furthermore, it is determined at which entry index a branch starts and at which exit index the branch stops. This information might be used to determine that every "loop" has at least one delayed transition. Example:

    EntryPort entry  [nEntry];
    ExitPort  exit   [nExit];
    Integer   indices[nEntry];
  equation
    Connections.uniqueRoot(entry, "...");
    indices = Connections.uniqueRootIndices(entry, exit, "...");
  

  ]

Modelica_StateGraph2.UsersGuide.ModelicaLicense2

All files in this directory (Modelica) and in all subdirectories, especially all files that build package "Modelica_StateGraph2" and all files in Modelica\Images are licensed by DLR and Dynasim under the Modelica License 2. 

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Frequently Asked Questions

This section contains questions/answer to users and/or distributors of Modelica packages and/or documents under Modelica License 2. Note, the answers to the questions below are not a legal interpretation of the Modelica License 2. In case of a conflict, the language of the license shall prevail.

Using or Distributing a Modelica Package under the Modelica License 2

What are the main differences to the previous version of the Modelica License?

1. Modelica License 1 is unclear whether the licensed Modelica package can be distributed under a different license. Version 2 explicitly allows that “Derivative Work” can be distributed under any license of Your choice, see examples in Section 1d) as to what qualifies as Derivative Work (so, version 2 is clearer).

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3. Modelica License 1 states that “It is not allowed to charge a fee for the original version or a modified version of the software, besides a reasonable fee for distribution and support“. Version 2 has a similar intention for all Original Work under Modelica License 2 (to remain free of charge and open source) but states this more clearly as “No fee, neither as a copyright-license fee, nor as a selling fee for the copy as such may be charged”. Contrary to version 1, Modelica License 2 has no restrictions on fees for Derivative Work that is provided under a different license (so, version 2 is clearer and has fewer restrictions).

4. Modelica License 2 introduces several useful provisions for the licensee (articles 5, 6, 12), and for the licensor (articles 7, 12, 13, 14) that have no counter part in version 1.

5. Modelica License 2 can be applied to all type of work, including documents, images and data files, contrary to version 1 that was dedicated for software only (so, version 2 is more general).

Can I distribute a Modelica package (under Modelica License 2) as part of my commercial Modelica modeling and simulation environment?

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Can I distribute a Modelica package (under Modelica License 2) under a different license when I first add classes to the package?

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Note, a “type” class (e.g., type Angle = Real(unit=”rad”)) can be copied and included unmodified under a commercial/proprietary license (for details, see the next question).

Can I copy a type class or part of a model, block, function, record, connector class, out of a Modelica package (under Modelica License 2) and include it modified or unmodified in a Modelica package under a commercial/proprietary license

Yes, according to article 2d), since this will in the end usually qualify as Derivative Work. The reasoning is the following: A type class or part of another class (e.g., an equation, a declaration, part of a class description) cannot be utilized “by its own”. In order to make this “usable”, you have to add additional code in order that the class can be utilized. This is therefore usually Derivative Work and Derivative Work can be provided under a different license. Note, this only holds, if the additional code introduced is sufficient to qualify for Derivative Work. Merely, just copying a class and changing, say, one character in the documentation of this class would be no Derivative Work and therefore the copied code would have to stay under Modelica License 2.

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Can I distribute a “save total model” under my commercial/proprietary license, even if classes under Modelica License 2 are included?

Your classes of the “save total model” can be distributed under your commercial/proprietary license, but the classes under Modelica License 2 must remain under Modelica License 2. This means you can distribute a “save total model”, but some parts might be under Modelica License 2.

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Yes. Note, if the encryption does not allow “copying” of classes (in to unencrypted Modelica source code), you have to send the Modelica source code of this package to your customer, if he/she wishes it, according to article 6.

Can I distribute an executable under my commercial/proprietary license, if the model from which the executable is generated uses models from a Modelica package under Modelica License 2?

Yes, according to article 2d), since this is seen as Derivative Work. The reasoning is the following: An executable allows the simulation of a concrete model, whereas models from a Modelica package (without pre-processing, translation, tool run-time library) are not able to be simulated without tool support. By the processing of the tool and by its run-time libraries, significant new functionality is added (a model can be simulated whereas previously it could not be simulated) and functionality available in the package is removed (e.g., to build up a new model by dragging components of the package is no longer possible with the executable).

Is my modification to a Modelica package (under Modelica License 2) a Derivative Work?

It is not possible to give a general answer to it. To be regarded as "an original work of authorship", a derivative work must be different enough from the original or must contain a substantial amount of new material. Making minor changes or additions of little substance to a preexisting work will not qualify the work as a new version for such purposes.

Using or Distributing a Modelica Document under the Modelica License 2

This section is devoted especially for the following applications:

1. A Modelica tool extracts information out of a Modelica package and presents the result in form of a “manual” for this package in, e.g., html, doc, or pdf format.

2. The Modelica language specification is a document defining the Modelica language. It will be licensed under Modelica License 2.

3. Someone writes a book about the Modelica language and/or Modelica packages and uses information which is available in the Modelica language specification and/or the corresponding Modelica package.

Can I sell a manual that was basically derived by extracting information automatically from a Modelica package under Modelica License 2 (e.g., a “reference guide” of the Modelica Standard Library):

Yes. Extracting information from a Modelica package, and providing it in a human readable, suitable format, like html, doc or pdf format, where the content is significantly modified (e.g. tables with interface information are constructed from the declarations of the public variables) qualifies as Derivative Work and there are no restrictions to charge a fee for Derivative Work under alternative 2d).

Can I copy a text passage out of a Modelica document (under Modelica License 2) and use it unmodified in my document (e.g. the Modelica syntax description in the Modelica Specification)?

Yes. In case you distribute your document, the copied parts are still under Modelica License 2 and you are not allowed to charge a license fee for this part. You can, of course, charge a fee for the rest of your document.

Can I copy a text passage out of a Modelica document (under Modelica License 2) and use it in modified form in my document?

Yes, the creation of Derivative Works is allowed. In case the content is significantly modified this qualifies as Derivative Work and there are no restrictions to charge a fee for Derivative Work under alternative 2d).

Can I sell a printed version of a Modelica document (under Modelica License 2), e.g., the Modelica Language Specification?

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Modelica_StateGraph2.UsersGuide.Contact

Main Authors:

Acknowledgements:

This library is based on the Modelica.StateGraph library and therefore the acknowledgement of the StateGraph library is repeated here:

• The development of the StateGraph was strongly motivated by the master thesis of Isolde Dressler (see literature), in which a compiler from JGrafChart to Modelica was designed and implemented. This project was supervised by Karl-Erik Arzen from Departement of Automatic Control, Lund Institut of Technology, Lund, Sweden.
• The StateGraph library profits also from the experience gained in the focused research program (Schwerpunktprogramm) "Continuous-Discrete Dynamic Systems" (KONDISK), sponsored by the Deutsche Forschungsgemeinschaft under grants OT174/1-2 and EN152/22-2. This support is most gratefully acknowledged.
• The implementation of the basic components of the StateGraph library by describing finite state machines with equations is based on (Elmqvist, Mattsson and Otter, 2001), which in turn uses ideas from (Mosterman, Otter and Elmqvist, 1998), see literature

The Modelica_StateGraph2 library is based on further ideas developed in (Malmheden et.al., 2008), see literature, and the prototype ModeGraph library developed by Martin Malmheden during his master thesis and for this article.

Partial financial support of DLR by BMBF (BMBF Förderkennzeichen: 01IS07022F) for the development of the Modelica_StateGraph2 library within the ITEA2 project EUROSYSLIB is highly appreciated.