Institute for Software Integrated SystemsVanderbilt University

Copyright © Vanderbilt University/ISIS 2008

Model Interpreters

Janos Mathebased on Peter Volgyesi’s slides

Implementing model transformations via model interpretation

April 19, 2023 2

Why do we need model interpreters ?

The metamodel describes the (abstract) syntax of the domain

The GME modeler tool does not “understand” the domain but enforces the syntax

The domain developer needs to define semantics Model interpreters (software plugins) Model transformations (graph rewriting

rules) Semantic anchoring (rewriting rules to a

well defined set of “semantic units”)

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Model InterpretersTypical uses

Text file generation (special case of rewriting) Source code Configurations files Documentation

Analysis & verification Simulation Model transformation & migration

Formal graph rewriting rules are preferred

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Model InterpretersHow do they work

The interpreter has (hard-coded) knowledge about the entities and relationships in the DSML Custom classes/interfaces/types The developer needs to keep the metamodel and the

interpreter in sync The modeler tool can invoke the interpreter

Upon user request On internally generated events (eg. “new obect added”)

Context The interpreter can traverse the model hierarchy, or processes only the event context

Actions Generates output (files, GUI windows, etc.) Can veto the model modification (if triggered from event)

eg: constraint manager Modifies the model

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Model Interpreters in GME

Interpreter DSML specific component Invoked explicitly by the user Most components fall into this category (eg.:

MetaInterpreter) Plug-in

Domain independent component Invoked explicitly by the user Eg.: Search plug-in, XML export/import

Add-on DSML specific or domain independent component Invoked on (model change) events Eg.: Constraint Manager

Interfaces

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GenericAPI

GenericAPI

MGADB

MGADB

SpecificAPI

SpecificAPI

SpecificAPI

SpecificAPI

SpecificAPI

SpecificAPI

Interpreters Interpreters

BON2Extender, UDM

COM, BON, BON2, JavaBON

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GME Internals

Storage Components

DB File

Core

Storage COM

MGA Meta

Core COM

MGA COM Meta COM

GUI

View Browser

Inspectr XMLConstraint Manager

Add-ons

Metainterpreter

Interpreters

Plug-ins

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GME Internals

Territories MGA library clients have at least one territory Objects are automatically added to them

One object can belong to multiple territories

When the object changes those clients will be notified whose territory contains the object

Transactions Consistent model database Undo/Redo operations Initiated within a territory

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COM InterfacesImplementation

Interfaces are defined in interface description files (.idl)

The IDL compiler generates C++ classes with virtual methods only

Library classes can “implement” these interfaces Using multiple inheritance Using aggregation

Library classes (COM objects) are created with factory methods exported from the library

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COM Objects and InterfacesExample

MgaModel

IMgaModel270B4F9A-B17C-11D3-9AD1-00AA00B6FE26

IMgaFCO270B4F98-B17C-11D3-9AD1-00AA00B6FE26

IMgaObject32D1F3A7-D276-11D3-9AD5-00AA00B6FE26

COM Interfaces COM Object

“Mga.MgaModel”83BA3237-B758-11D3-ABAE-000000000000

•Stored in the Windows Registry•Used when a new object is requested

•Stored in the library code (class)•Used when a new interface is requested•IUnknown is always supported

See the “Interfaces” folder in the GME program directory

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Problems with COM

Steep learning curve Error-prone low-level details

Eg.: COM strings (BSTR), output parameters, reference counting

However: very efficient components (almost zero

overhead) some components (eg.: add-ons) can be

implemented in raw COM only

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High level interfaces

Builder Object Network (BON) C++ classes (custom DSML specific classes can be

defined) The entire model hierarchy is created/duplicated in

memory initially Very limited model modification support

BON2 and MON C++ classes and meta classes (custom DSML specific

classes can be defined) BON2 objects are created on-demand Full support for modifying the GME model

JavaBON Python, Visual Basic support

Basically raw COM with minimal infrastructure support

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Meta Object Network

Programmatic access to the paradigm (abstract syntax)

Similar to the introspection/reflection APIs in OOP languages

Every object in BON2 has a reference to one of these classes

Wrapper classes around the Meta COM library See: architecture diagram

The classes are defined in the “MON::” namespace

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Meta Object NetworkEntities

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Meta Object NetworkRelations

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BON2

Layered architecture COM layer (interface with Mga and Meta). Hidden

from the developer Implementation layer

High level API mapping to raw COM Object caching Eg.: “BON::FCOImpl”

Wrapper layer The “real” API for the interpreter developer Pointer-like interface (smart pointers) Eg.: “BON::FCO”

Classes are defined in the “BON::” namespace

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BON2 Wrapper Classes

Pointer interface use “->” to access the contained

(implementation class) method

Validity of the object boolean (“!“) operators

Equality (between MGA objects) “=“, “!=“ operators

Smart casting The cast operation succeeds if the MGA

object can be encapsulated with the target class

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BON2 Implementation Classes

Objects are created on-demand and cached

Multiple wrapper objects can contain the same implementation object

Impl. objects are released if there is no reference to them from wrapper classes Reference counting is automatic Slight differences between add-ons and

interpreters

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BON2 Components

The interpreter is represented by “BON::Component”

The following methods need to be implemented

void Component::initialize( … ) void Component::finalize( … ) void Component::invokeEx( … )

Entry point for interpreters and plug-ins

void Component::globalEventPerformed( … ) void Component::objectEventPerformed( … )

“Entry point” for add-ons

FSM Example

1. Metamodel Create an FSM metamodel using MetaGME

2. Models Build FSMs (models) using the FSM

metamodel

3. Interpreter Translate FSM models to executable code

4. Execution of a model Feed events to the FSM thus causing state

changes

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Creating an interpreter

Create, register CreateNewComponent.exe at GME install dir

By default at C:\Program Files\GME\SDK Implement

Use MS Visual Studio 2003/2005 to implement the interpreter logic

Run Invoke the interpreter in GME by clicking on the dedicated

button Create executable

Take the generated C++ file and build it DOS PROMPT> cl TestFSM.cpp

Execute Run the generated TestFSM.exe file Feed events (by typing “a” and hitting Enter), when finished type “exit”

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FSM interpreter logic

Start: Project root1. Find FSM models2. Iterate through FSMs

a) Create and open source file in a specific folder

b) Traverse FSM model and generate codec) Close file

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BON2 Extension Classes

Extendable classes: FCO, Atom, Model, Connection, Set, Reference

Realizing a new implementation class

class CustomImpl : public BON::ModelImpl{

public:void initalize() { … }void finalize() { … }…

};

Create a new wrapper class

DECLARE_BONEXTENSION( BON::Model, CustomImpl, Custom );

IMPLEMENT_BONEXTENSION( Compound, “Compound” );

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BON2 Extension Classes

Support for abstract base classes: DECLARE_ABSTRACT_BONEXTENSION IMPLEMENT_ABSTRACT_BONEXTENSION

Multiple inheritance: DECLARE_BONEXTENSION2 DECLARE_BONEXTENSION3

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Essential BON2 Classes

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BON Extender

Automatically generates BON2 extension classes from the metamodel For all (even abstract) classes

Container classes will have customized “get” methods for the contained roles

Connections will have specialized source and destination “get” methods

Customized “get” methods for attributes User code is protected and preserved by

special comments “//BUP” “//EUP”