Model driven software engineering in practice book - chapter 7 - Developing your own modeling language

Marco Brambilla, Jordi Cabot, Manuel Wimmer.
Model-Driven Software Engineering In Practice. Morgan & Claypool 2012.
Teaching material for the book
Model-Driven Software Engineering in Practice
by Marco Brambilla, Jordi Cabot, Manuel Wimmer.
Morgan & Claypool, USA, 2012.
Copyright © 2012 Brambilla, Cabot, Wimmer.
www.mdse-book.com
DEVELOPING YOUR OWN
MODELING LANGUAGE
Chapter 7

Content
•  Introduction
•  Abstract Syntax
•  Graphical Concrete Syntax
•  Textual Concrete Syntax

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INTRODUCTION

Introduction
What to expect from this lecture?
§  Motivating example: a simple UML Activity diagram
§  Activity, Transition, InitialNode, FinalNode
§  Question: Is this UML Activity diagram valid?
§  Answer: Check the UML metamodel!
§  Prefix „meta“: an operation is applied to itself
§  Further examples: meta-discussion, meta-learning, …
§  Aim of this lecture: Understand what is meant by the term
„metamodel“ and how metamodels are defined.
ad Course workflow
Study content Write examAttend lecture

Introduction
Anatomy of formal languages 1/2
§  Languages have divergent goals and fields of application,
but still have a common definition framework
Semantics
Abstract Syntax
Concrete Syntax
Formal languages
Meaning of
language elements
Language elements,
i.e., grammar
Notation of
language elements
1..1
1..*
1..*
1..*

Introduction
Anatomy of formal languages 2/2
§  Main components
§  Abstract syntax: Language concepts and how these concepts can be
combined (~ grammar)
§  It does neither define the notation nor the meaning of the concepts
§  Concrete syntax: Notation to illustrate the language concepts intuitively
§  Textual, graphical or a mixture of both
§  Semantics: Meaning of the language concepts
§  How language concepts are actually interpreted
§  Additional components
§  Extension of the language by new language concepts
§  Domain or technology specific extensions, e.g., see UML Profiles
§  Mapping to other languages, domains
§  Examples: UML2Java, UML2SetTheory, PetriNet2BPEL, …
§  May act as translational semantic definition

Excursus: Meta-languages in the Past
Or: Metamodeling – Old Wine in new Bottles?
§  Formal languages have a long tradition in computer science
§  First attempts: Transition from machine code instructions to high-
level programming languages (Algol60)
§  Major successes
§  Programming languages such as Java, C++, C#, …
§  Declarative languages such as XML Schema, DTD, RDF, OWL, …
§  Excursus
§  How are programming languages and XML-based languages defined?
§  What can thereof be learned for defining modeling languages?

Programming languages
Overview
§  John Backus and Peter Naur invented formal languages for the
definition of languages called meta-languages
§  Examples for meta-languages: BNF, EBNF, …
§  Are used since 1960 for the definition of the syntax of
programming languages
§  Remark: abstract and the concrete syntax are both defined
§  EBNF Example
Java := [PackageDec] {ImportDec} ClassDec;
PackageDec := “package” QualifiedIdentifier;
ImportDec := “import” QualifiedIdenfifier;
ClassDec := Modifier “class” Identifier [“extends” Identifier]
[“implements” IdentifierList] ClassBody;
production rule terminal
option sequence non-terminal

Example: MiniJava
§  Grammar
§  Program
§  Validation: does the program conform to the grammar?
§  Compiler: javac, gcc, …
§  Interpreter: Ruby, Python, …
Java := [PackageDec] {ImportDec} ClassDec;
PackageDec := “package” QualifiedIdentifier;
ImportDec := “import” QualifiedIdenfifier;
ClassDec := Modifier “class” Identifier [“extends” Identifier]
[“implements” IdentifierList] ClassBody;
Modifier := “public” | “private” | “protected”;
Identifier := {“a”-”z” | “A”-”Z” | “0”-”9”}
package mdse.book.example;
import java.util.*;
public class Student extends Person { … }

Meta-architecture layers
§  Four-layer architecture
M1-Layer
M2-Layer
M3-Layer
Execution of the
program
package mdse.book.example;
public class Student
extends Person { … }
Java := [PackageDec]
{ImportDec} ClassDec;
PackageDec := “package“
QualifiedIdentifier; …
EBNF := {rules};
rules := Terminal | Non-Terminal |...
Definition of EBNF in
EBNF – EBNF grammar
(reflexive)
Definition of Java in
EBNF – Java grammar
Program – Sentence
conform to the grammar
M0-Layer

<!ELEMENT cookbook (title, meal+)>
<!ELEMENT title (#PCDATA)>
<!ELEMENT meal (ingredient+)>
<!ELEMENT ingredient>
<!ATTLIST ingredient name CDATA #REQUIRED
amount CDATA #IMPLIED
unit CDATA #IMPLIED>
attributes
1..1
element
0..1
contentParticle 1..*
XML-based languages
Overview
§  XML files require specific structures to allow for a standardized
and automated processing
§  Examples for XML meta languages
§  DTD, XML-Schema, Schematron
§  Characteristics of XML files
§  Well-formed (character level) vs. valid (grammar level)
§  DTD Example

XML-based languages
Example: Cookbook DTD
§  DTD
§  XML
§  Validation
§  XML Parser: Xerces, …
<!ELEMENT cookbook (title, meal+)>
<!ELEMENT title (#PCDATA)>
<!ELEMENT meal (ingredient+)>
<!ELEMENT ingredient>
<!ATTLIST ingredient name CDATA #REQUIRED
amount CDATA #IMPLIED
unit CDATA #IMPLIED>
<cookbook>
<title>How to cook!</title>
<meal name= „Spaghetti“ >
<ingredient name = „Tomato“, amount=„300“ unit=„gramm“>
<ingredient name = „Meat“, amount=„200“ unit=„gramm“> …
</meal>
</cookbook>

XML-based languages
Meta-architecture layers
§  Five-layer architecture (was revised with XML-Schema)
M1-Layer
M2-Layer
M4-Layer
Concrete entities (e.g.: Student “Bill Gates”)
<javaProg>
<packageDec>mdse.book.example</packageDec>
<classDec name=„Student“ extends=„Person“/>
</javaProg>
<!ELEMENT javaProg (packageDec*,
importDec*, classDec)>
<!ELEMENT packageDec (#PCDATA)>
Definition of EBNF
in EBNF
Definition of Java in
DTD – Grammar
XML –
conform to the DTD
M0-Layer
M3-Layer
ELEMENT := „<!ELEMENT “ Identifier „>“
ATTLIST;
ATTLIST := „<!ATTLIST “ Identifier …
Definition of DTD
in EBNF
EBNF := {rules};
rules := Terminal | Non-Terminal |...

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ABSTRACT SYNTAX

Introduction
Spirit and purpose of metamodeling 1/3
§ Metamodel-centric language design:
All language aspects base on the abstract syntax of the
language defined by its metamodel
Metamodel
Textual
Concrete Syntaxes
Graphical
Concrete Syntaxes
Models
Model 2 Model
Transformations
Model 2 Text
Transformations
Modeling
Constraints

Introduction
§ Advantages of metamodels
§ Precise, accessible, and evolvable language definition
§ Generalization on a higher level of abstraction
by means of the meta-metamodel
§ Language concepts for the definition of metamodels
§ MOF, with Ecore as its implementation, is considered as a universally
accepted meta-metamodel
§ Metamodel-agnostic tool support
§ Common exchange format, model repositories, model editors, model
validation and transformation frameworks, etc.

Introduction
Meta-Metamodel Meta-
Language
Metamodel
Model System
Language
represents
defines
defines
MOF, Ecore
UML, ER, …
Examples
Model
Instance
System
Snapshot
represents
UniSystem, …
A UniSystem
Snapshot
Language
Engineering
Domain
Engineering
«conformsTo»
M3
M2
M1
M0
4-layer Metamodeling Stack
«conformsTo»
«conformsTo»
«conformsTo»

Metamodel development process
Incremental and Iterative
Modeling
domain
analysis
Modeling
language
design
Modeling
language
validation
Identify purpose, realiza-
tion, and content of the
modeling language
Sketch reference
modeling examples
Formalize modeling
language by defining
a metamodel
Formalize modeling
constraints using OCL
Instantiate metamodel
by modeling reference
models
Collect feedback for
next iteration

MOF - Meta Object Facility
Introduction 1/3
§  OMG standard for the definition of metamodels
§  MOF is an object-orientated modeling language
§  Objects are described by classes
§  Intrinsic properties of objects are defined as attributes
§  Extrinsic properties (links) between objects are defined as associations
§  Packages group classes
§  MOF itself is defined by MOF (reflexive) and divided into
§  eMOF (essential MOF)
§  Simple language for the definition of metamodels
§  Target audience: metamodelers
§  cMOF (complete MOF)
§  Extends eMOF
§  Supports management of meta-data via enhanced services (e.g. reflection)
§  Target audience: tool manufacturers

Introduction 2/3
§  Offers modeling infrastructure not only for MDA, but for MDE in
general
§  MDA dictates MOF as meta-metamodel
§  UML, CWM and further OMG standards are conform to MOF
§  Mapping rules for various technical platforms defined for MOF
§  XML: XML Metadata Interchange (XMI)
§  Java: Java Metadata Interfaces (JMI)
§  CORBA: Interface Definition Language (IDL)

Introduction 3/3
§  OMG language definition stack
MOF Model
Models
ModelsUML
Models
IDL
Metamodel
CWM
Metamodel
Models
ModelsIDL
Interfaces
Models
ModelsCWM
Models
M3-Layer
Meta-Metamodel
UML
Metamodel
M2-Layer
Metamodel
M1-Layer
Model
M0-Layer
Instances

Why an additional language for M3
… isn‘t UML enough?
§  MOF only a subset of UML
§  MOF is similar to the UML class diagram, but much more limited
§  No n-ary associations, no association classes, …
§  No overlapping inheritance, interfaces, dependencies, …
§  Main differences result from the field of application
§  UML
§  Domain: object-oriented modeling
§  Comprehensive modeling language for various software systems
§  Structural and behavioral modeling
§  Conceptual and implementation modeling
§  MOF
§  Domain: metamodeling
§  Simple conceptual structural modeling language
§  Conclusion
§  MOF is a highly specialized DSML for metamodeling
§  Core of UML and MOF (almost) identical

MOF – Meta Object Facility
Language architecture of MOF 2.0
MOF 2.0
cMOFeMOF
Extended
reflection and
OO concepts
Minimal OO
language range
ReflectionExtension
Identity
Extension-
mechanism
Self-
reflection
Unambiguous
identification

§  Abstract classes of eMOF
§  Definition of general properties
§  NamedElement
§  TypedElement
§  MultiplicityElement
§  Set/Sequence/OrderedSet/Bag
§  Multiplicities
Object
TypedElementType
isInstance(element:Element): Boolean
MultiplicityElement
isOrdered: Boolean = false
isUnique: Boolean = true
lower: Integer
upper: UnlimitedNatural
NamedElement
name:String
type
0..1
Element
Taxonomy of
abstract classes

§  Core of eMOF
§  Based on object-orientation
§  Classes, properties, operations, and parameters
Type
Property
isReadOnly: Boolean = false
default: String [0..1]
isComposite: Boolean = false
isDerived: Boolean = false
*superclass
TypedElement MultiplicityElement
Operation
Parameter
Type
ownedParameter
*
ownedAttribute
0..1 *
ownedOperation
0..1
raisedException
*
isAbstract: Boolean
Class
*
opposite
0..1

Classes
§  A class specifies structure and behavior of
a set of objects
§  Intentional definition
§  An unlimited number of instances (objects) of a
class may be created
§  A class has an unique name in its
namespace
§  Abstract classes cannot be instantiated!
§  Only useful in inheritance hierarchies
§  Used for »highlighting« of
common features of a set of subclasses
§  Concrete classes can be instantiated!
Class
MOF
Transition
Activity
Event
Example
name : String
isAbstract : boolean

Generalization
§  Generalization: relationship between
§  a specialized class (subclass) and
§  a general class (superclass)
§  Subclasses inherit properties of their
superclasses and may add further
properties
§  Discriminator: „virtual“ attribute used for the
classification
§  Disjoint (non-overlapping) generalization
§  Multiple inheritance
TimeEvent
Event
CallEvent
0..* superclasses
Class
MOF
Example

MOF
Attributes
§  Attributes describe inherent characteristics
of classes
§  Consist of a name and a type (obligatory)
§  Multiplicity: how many values can be stored
in an attribute slot (obligatory)
§  Interval: upper and lower limit are natural
numbers
§  * asterisk - also possible for upper limit
(Semantics: unlimited number)
§  0..x means optional: null values are allowed
§  Optional
§  Default value
§  Derived (calculated) attributes
§  Changeable: isReadOnly = false
§  isComposite is always true for attributes
* ownedAttribute
TimeEvent
Event
CallEvent
Example
id: Integer [1..1]
kinds: String
[1..*]
synchronized
: boolean =
true [0..1]
Property
isReadOnly: Boolean
default: String[0..1]
isComposite:
Boolean
isDerived: Boolean
Class

Associations
§  An association describes the common structure of a set of
relationships between objects
§  MOF only allows unary and binary associations, i.e., defined
between two classes
§  Binary associations consist of two roles whereas each role has
§  Role name
§  Multiplicity limits the number of partner objects of an object
§  Composition
§  „part-whole” relationship (also “part-of” relationship)
§  One part can be at most part of one composed object at one time
§  Asymmetric and transitive
§  Impact on multiplicity: 1 or 0..1

§  Association
§  Composition
Associations - Examples
A B
1..* *
multiplicity
role name
b
A B
0..1 *
C
A
0..1
*
B
*
{xor}
0..1
Syntax ü
Semantics ü
C
A
1
*
B
*
Syntax ü
Semantics û
1
Example 1 Example 2 Example 3
a

Example
Packages
§  Packages serve as a
grouping mechanism
§  Grouping of related types, i.e., classes,
enumerations, and primitive types.
§  Partitioning criteria
§  Functional or information cohesion
§  Packages form own namespace
§  Usage of identical names in different
parts of a metamodel
§  Packages may be nested
§  Hierarchical grouping
§  Model elements are contained in
one package
Package
NamedElement
name:String
Type
0..*
+nestingPackage
+nestedPackage
0..*
0..1
0..1
X
MOF
Y Z
X
A B
C
A B

Types 1/2
§  Primitive data types: Predefined types for integers, character strings
and Boolean values
§  Enumerations: Enumeration types consisting of named constants
§  Allowed values are defined in the course of the declaration
§  Example: enum Color {red, blue, green}
§  Enumeration types can be used as data types for attributes
NamedElement
name:String
Type
DataType
PrimitiveType Enumeration EnumerationLiteralenumeration ownedLiteral
{ordered} 0..*0..1
<<primitive>>
Integer
<<primitive>>
Boolean
<<primitive>>
String
<<primitive>>
UnlimitedNatural*
*) represents unlimited number (asterisk) – only for
the definition of the upper limits of multiplicities

Types 2/2
§  Differentiation between value types and reference types
§  Value types: contain a direct value (e.g., 123 or ‘x‘)
§  Reference types: contain a reference to an object
§  Examples
Types
Value types Reference types
Primitive types Enumerations Classes
user-defined types
Boolean Integer String
Car
color: String
Car
color: Color • red
• green
• blue
«enumeration»
Color
Car Person
Primitive types Enumerations Reference types
owner1..1

Example 1/9
§  Activity diagram example
§  Concepts: Activity, Transition, InitialNode, FinalNode
§  Domain: Sequential linear processes
§  Question: How does a possible metamodel to this language look
like?
§  Answer: apply metamodel development process!
ad Course workflow
Study
content
Write
exam
Attend
lecture

Syntax Concept
ActivityDiagram
FinalNode
InitialNode
Activity
Transition
name
ad name
Example 2/9
Identification of the modeling concepts
ad Course workflow
Study
content
Write
exam
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lecture
Example model = Reference Model
Notation table

Example 3/9
Determining the properties of the modeling concepts
Concept
Intrinsic
properties
Extrinsic
properties
ActivityDiagram Name 1 InitialNode
1 FinalNode
Unlimited number of Activities and Transitions
FinalNode - Incoming Transitions
InitialNode - Outgoing Transitions
Activity Name Incoming and outgoing Transitions
Transition - Source node and target node
Nodes: InitialNode, FinalNode, Activity
Study
content
Write
exam
Attend
lecture
ad Course workflow
Example model
Modeling concept table

Example 4/9
Object-oriented design of the language
Concept Intrinsic properties Extrinsic properties
ActivityDiagram Name 1 InitialNode
1 FinalNode
Unlimited number of Activities and Transitions
FinalNode - Incoming Transition
InitialNode - Outgoing Transition
Activity Name Incoming and outgoing Transition
Transition - Source node and target node
Nodes: InitialNode, FinalNode, Activity
Attribute AssociationClass
MOF
FinalNode
InitialNode
ActivityDiagram
name : String
Metamodel
1
1
1..*
1..*
1
1
0..1
1incoming outgoing
incoming
outgoing
target source
source
target
0..1
0..1
Transition
Activity
name : String
0..1
0..1
1

name=“Course workflow”
Example 5/9
Overview
FinalNode
InitialNode
ActivityDiagram
name : String
Metamodel
1
1
*
*
1
1
1 1incoming outgoing
incoming
outgoing
target source
source
target
0..1
Transition
Activity
name : String
Study
content
Write
exam
Attend
lecture
ad Course workflow
Model
Abstract
syntax
Concrete
syntax
2:InitialNode
1:ActivityDiagram
3:FinalNode
4:Activity 5:Activity 6:Activity
7:Transition 8:Transition 9:Transition 10:Transition
name=„Attend..” name=„Study…“ name=„Write…“
0..1
0..1
0..1
“bi-directional link”
“uni-directional link”

Example 6/9
Applying refactorings to metamodels
FinalNode InitialNode
ActivityDiagram
name : String
Metamodel
*
*
0..1 0..1incoming outgoing
target source1
Transition
Node
name : String
OCLConstraints
1
context ActivityDiagram
inv: self.nodes -> exists(n|n.isTypeOf(FinalNode))
inv: self.nodes -> exists(n|n.isTypeOf(InitialNode))
context FinalNode
inv: self.outgoing.oclIsUndefined()
context InitialNode
inv: self.incoming.oclIsUndefined()
context ActivityDiagram
inv: self.name <> '' and self.name <> OclUndefined …
ActivityNode

Example 7/9
Impact on existing models
ActivityDiagram
name : String
Metamodel
*
*
1..* 1..*incoming outgoing
target source1
Transition
Node
name : String
Model
1
ActivityNode
Abstract
syntax
2:InitialNode
1:ActivityDiagram
3:FinalNode
4:Activity 5:Activity 6:Activity
name=„Att…“ name=„Study…“ name=„Write…“
Validation errors:
û  Class Activity is unknown,
û  Reference finalNode, initialNode, activity are unknown
Changes:
§  Deletion of class Activity
§  Addition of class ActivityNode
§  Deletion of redundant references

Example 8/9
How to keep metamodels evolvable when models already exist
§  Model/metamodel co-evolution problem
§  Metamodel is changed
§  Existing models eventually become invalid
§  Changes may break conformance relationships
§  Deletions and renamings of metamodel elements
§  Solution: Co-evolution rules for models coupled to metamodel
changes
§  Example 1: Cast all Activity elements to ActivityNode elements
§  Example 2: Cast all initialNode, finalNode, and activity links to node links

Example 9/9
Adapted model for new metamodel version
ActivityDiagram
name : String
Metamodel
*
*
1..* 1..*incoming outgoing
target source1
Transition
Node
name : String
Model
1
ActivityNode
Abstract
syntax
2:InitialNode
1:ActivityDiagram
3:FinalNode
4:ActivityNode 5:ActivityNode
6:ActivityNode
name=„Attend…“ name=„Study…“
name=„Write…“
More on this topic in Chapter 10!

Excursus: Metamodeling – everything new? 1/3
§  A language may be defined by meta-languages from different
Technical Spaces (TS)
§  Attention: Each TS has its (dis)advantages!
Java
DTD
Java
Document
Java
Metamodel
Java
Model
Java
Grammar
Java
Program
Grammarware Modelware XMLware

Correspondence between EBNF and MOF
§  Mapping table (excerpt)
§  Example
EBNF MOF
Production Composition
Non-Terminal Class
Sequence Multiplicity: 0..*
Model
Class
1
*
**
Grammar Metamodel
AttributeName Method
C
Model ::= {Class}
Class ::= Name {Attribute}
{Method}

Correspondence between DTD and MOF
§  Mapping table (excerpt)
§  Example
DTD MOF
Item Composition
Element Class
Cardinality * Multiplicity 0..*
Model
Class
1
*
**
DTD Metamodel
AttributeName Method
C
<!ELEMENT Model (Class*)>
<!ELEMENT Class (Name,
Attribute*, Method*)>

Ecore
Introduction
§  Ecore is the meta-metamodel of the Eclipse Modeling
Frameworks (EMF)
§  www.eclipse.org/emf
§  Ecore is a Java-based implementation of eMOF
§  Aims of Ecore
§  Mapping eMOF to Java
§  Aims of EMF
§  Definition of modeling languages
§  Generation of model editors
§  UML/Java/XML integration framework

Ecore
Taxonomy of the language concepts
EObject
EModelElement
EFactory ENamedElement
EPackage EClassifier EEnumLiteral ETypedElement
EClass
EAttribute
EStructuralFeature EOpertation EParameter
EDataType
EEnum
EReference
equivalent to java.lang.object
encapsulates reflection mechanism (only
programming level)
object creation
(only programming level)
Programming concepts
Abstract modeling concepts
Concrete modeling concepts

Ecore
Core
§  Based on object-orientation (as eMOF)
§  Classes, references, attributes, inheritance, …
§  Binary associations are represented as two references
§  Data types are based on Java data types
§  Multiple inheritance is resolved by one „real“ inheritance and multiple
implementation inheritance relationships
eReferences
0..*
eAttributes
EReference
name: String
containment:boolean
lowerBound: int
upperBound: int
EClass
name: String
EAttribute
name: String
EDataType
name: String10..*
0..* eSuperTypes
1
0..1eOpposite
to

Ecore
Binary associations
§ A binary association demands for two references
§ One per association end
§ Both define the respective other one as eOpposite
eReferences
0..*
1
0..1eOpposite
to
EClass
C1:EClass
C2:EClass
r1:EReference
r2:EReference
C1 C2
r1r2to
toeOpposite
eOpposite
Ecore
MM (abstract syntax) MM (concrete syntax)
name: String
containment: boolean
lowerBound: int
upperBound: int
EReference

Ecore
Data types
§ List of Ecore data types (excerpt)
§ Java-based data types
§ Extendable through self-defined data types
§  Have to be implemented by Java classes
Ecore data type Primitive type or class (Java)
EBoolean boolean
EChar char
EFloat float
EString java.lang.String
EBoolanObject java.lang.Boolean
… …

Ecore
Multiple inheritance
§  Ecore supports multiple inheritance
§  Unlimited number of eSuperTypes
§  Java supports only single inheritance
§  Multiple inheritance simulated by implementation of interfaces!
§  Solution for Ecore2Java mapping
§  First inheritance relationship is used as „real“ inheritance relationship using
«extend»
§  All other inheritances are interpreted as specification inheritance
«implements»
EClass
name: String
0..* eSuperTypes
ClassC
ClassBClassA
«extend»
class ClassC
extends ClassA
implements ClassB
Java code
«implements»

§ Class diagram – Model TS
§ Annotated Java (Excerpt) – Program TS
§ XML (Excerpt) – Document TS
<xsd:complexType name=“Appointment”>
<xsd:element name=“description” type=“Description”
minOccurs=“0” maxOccurs=“unbounded” />
</xsd:complexType>
Ecore
Concrete syntax for Ecore models
*
Appointment
name: String
place: String
Description
text: String
public interface Appointment{
/* @model type=“Description” containment=“true” */
List getDescription();
}

Summary
Ecore modeling elements at a glance

Eclipse Modeling Framework
What is EMF?
§  Pragmatic approach to combine modeling and programming
§  Straight-forward mapping rules between Ecore and Java
§  EMF facilitates automatic generation of different
implementations out of Ecore models
§  Java code, XML documents, XML Schemata
§  Multitude of Eclipse projects are based on EMF
§  Graphical Editing Framework (GEF)
§  Graphical Modeling Framework (GMF)
§  Model to Model Transformation (M2M)
§  Model to Text Transformation (M2T)
§  …

Metamodeling Editors
§  Creation of metamodels via
§  Tree-based editors (abstract syntax)
§  Included in EMF
§  UML-based editors (graphical concrete syntax)
§  e.g., included in Graphical Modeling Framework
§  Text-based editors (textual concrete syntax)
§  e.g., KM3 and EMFatic
§  All types allow for a semantically equivalent metamodeling
Tree-based editor UML-based editor Text-based editor

Model editor generation process
Metamodel Model editor
?
Example: MiniUML metamodel -> MiniUML model editor
How can a model editor be created out of a metamodel?
?

Step 1 – Create metamodel (e.g., with tree editor)
Save XMI
Generate GenModel
Create MM
UML.ecore
UML.genmodel
ModelTSCodeTS
Code generation
MM in Memory

Step 2 – Save metamodel
<?xml version="1.0" encoding="UTF-8"?>
<ecore:EPackage xmi:version="2.0"
xmlns:xmi="http://www.omg.org/XMI"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-
instance"
xmlns:ecore="http://www.eclipse.org/emf/2002/
Ecore"
name="uml"
nsURI="http://uml" nsPrefix="uml">
<eClassifiers xsi:type="ecore:EClass"
name="NamedElement">
<eStructuralFeatures xsi:type="ecore:EAttribute"
name="name" eType="ecore:EDataType
http://www.eclipse.org/emf/2002/
Ecore#//EString"/>
</eClassifiers>
<eClassifiers xsi:type="ecore:EClass" name="Class"
eSuperTypes="#//NamedElement">
<eStructuralFeatures xsi:type="ecore:EReference"
name="ownedAttribute" upperBound="-1"
eType="#//Property"
eOpposite="#//Property/owningClass"/>
<eStructuralFeatures xsi:type="ecore:EAttribute"
name="isAbstract"
eType="ecore:EDataType
http://www.eclipse.org/emf/2002/
Ecore#//EBoolean"/>
</eClassifiers>
</ecore:EPackage>
UML.ecore
Save XMI
Generate GenModel
Create MM
UML.ecore
UML.genmodel
ModelTSCodeTS
Code generation
MM in Memory

Step 3 – Generate GenModel
GenModel specifies properties for
code generation
Save XMI
Generate GenModel
Create MM
UML.ecore
UML.genmodel
ModelTSCodeTS
Code generation
MM in Memory

For each meta-class we get:
§  Interface: Getter/setter for attributes and references
§  Implementation class:
Getter/setter implemented
§  Factory for the creation of model elements,
for each Package one Factory-Class is created
Step 4 – Generate model code
public interface Class extends NamedElement {
EList getOwnedAttributes();
boolean isIsAbstract();
void setIsAbstract(boolean value);
}
public class ClassImpl
extends NamedElementImpl implements Class{
public EList getOwnedAttributes() {
return ownedAttributes;
}
public void setIsAbstract(boolean
newIsAbstract) {
isAbstract = newIsAbstract;
}
}
ModelTSCodeTS
Create MM
Generate
Editor
Model Code
UML.genmodel
Edit Code Editor Code

Step 5 – Generate edit code
§  UI independent editing
support for models
§  Generated artifacts
§  TreeContentProvider
§  LabelProvider
§  PropertySource
ModelTSCodeTS
Create MM
Generate
Editor
Model Code
UML.genmodel

Step 6 – Generate editor code
§  Editor as Eclipse Plugin
or RCP Application
§  Generated artifacts
§ Model creation wizard
§ Editor
§ Action bar contributor
§ Advisor (RCP)
§ plugin.xml
§ plugin.properties
ModelTSCodeTS
Create MM
Generate
Editor
Model Code
UML.genmodel

63
Start the modeling editor
Plugin.xml
RCP Application
Click here to start!

Metamodels are compiled to Java!
§  Metamodeling mistake or error in EMF code generator?

Metamodels are compiled to Java!
§  Attention
§  Only use valid Java identifier as names
§  No blanks, no digits at the beginning, no special characters, …
§  NamedElements require a name
§  Classes, enumerations, attributes, references, packages
§  Attributes and references require a type
§  Always use the validation service prior to the code generation!!!

Shortcut for Metamodel Instantiation
Metamodel Registration, Dynamic Model Creation, Reflective Editor
§  Rapid testing by
1)  Registration of the metamodel
2)  Select root node (EClass) and create dynamic instance
3)  Visualization and manipulation by Reflective Model Editor
1) Register EPackages 2) Create Dynamic Instance 3) Use Reflective Editor

OCL support for EMF
Several Plugins available
§  Eclipse OCL Project
§  http://www.eclipse.org/projects/project.php?id=modeling.mdt.ocl
§  Interactive OCL Console to query models
§  Programming support: OCL API, Parser, …
§  OCLinEcore
§  Attach OCL constraints by using EAnnotations to metamodel classes
§  Generated modeling editors are aware of constraints
§  Dresden OCL
§  Alternative to Eclipse OCL
§  OCL influenced languages, but different syntax
§  Epsilon Validation Language residing in the Epsilon project
§  Check Language residing in the oAW project

www.mdse-book.com
GRAPHICAL CONCRETE
SYNTAX

Metamodel Visual Notation
Model Diagram/Text
visualizes
symbolizes
«conformsTo» «conformsTo»
Introduction
§ The visual notation of a model language is referred as
concrete syntax
§ Formal definition of concrete syntax allows for automated
generation of editors
§ Several approaches and frameworks available for defining
concrete syntax for model languages

Introduction
§ Several languages have no formalized definition of their
concrete syntax
§ Example – Excerpt from the UML-Standard

Introduction
§  Concrete syntax improves the readability of models
§  Abstract syntax not intended for humans!
§  One abstract syntax may have multiple concrete ones
§  Including textual and/or graphical
§  Mixing textual and graphical notations still a challenge!
§  Example – Notation alternatives for the creation of an appointment
Notation
alternative 1:
Notation
alternative 2:
Notation
alternative 3:
Appointment a;
a = new Appointment;
EnterKeyData (a);
Create
Appointment
Enter
KeyData
Appointment Appointment
Create
Appointment Appointment
Enter
KeyData

Introduction
Concrete Syntaxes in Eclipse
Generic tree-based
EMF Editor
Ecore-based Metamodels
Graphical Concrete Syntax
Textual Concrete Syntax

Anatomy of Graphical Concrete Syntaxes
§ A Graphical Concrete Syntax (GCS) consists of
§ graphical symbols,
§  e.g., rectangles, circles, …
§ compositional rules,
§  e.g., nesting of elements, …
§ and mapping between graphical symbols and abstract syntax
elements.
§  e.g., instances of a meta-class are visualized by rounded rectangles in
the GCS
Activity
name : String
Attend
lecture
4:Activity
name=„Attend lecture”

Anatomy of Graphical Modeling Editors
Outline View
Tool Palette
Modeling Canvas
Project Browser
Property View

Features of Graphical Modeling Editors
Action Bars:
Collapsed Compartments:
Connection Handles:
Geometrical Shapes:

Features of Graphical Modeling Editors
Actions:
Toolbar:
Properties View:

Line
Figure
Edge
Node Compartment
Shape
Rectangle Ellipse …
Label
DiagramElementDiagram
Metamodel Element
Mapping
1..1
1..1
1..1
1..1
Compound
Figure
1..*1..*
Abstract
Syntax
(AS)
Concrete
Syntax
(CS)
Class
Association
Attribute
AS2CS
Generic Metamodel for GCS

GCS Approaches
§ Mapping-based
§ Explicit mapping model between
abstract syntax, i.e., the
metamodel, and concrete syntax
§ Annotation-based
§ The metamodel is annotated with
concrete syntax information
§ API-based
§ Concrete syntax is described by a
programming language using a
dedicated API for graphical
modeling editors
Abstract Syntax Concrete Syntax
AS2CS
Abstract Syntax Concrete Syntax
Abstract Syntax
Concrete SyntaxMM API

Mapping-based Approach: GMF
Basic Architecture of GMF
n  “The Eclipse Graphical Modeling Framework (GMF) provides a
generative component and runtime infrastructure for developing
graphical editors based on EMF and GEF.” - www.eclipse.org/gmf
Graphical
Editor
EMF Runtime
generate
GEF Runtime
GMF Runtime
GMF Tools
«uses»«uses» «uses»
«uses» «uses»

Mapping-based Approach: GMF
Tooling Component
Domain
Model
(ECore)
CodeGen Model
(EMF GenModel)
Java
code
Generator Model
(GMFGenModel)
Java
code
Tool Definition
(GMFTool)
Graphical
Definition
(GMFGraph)
Mapping
(GMFMap)
Domain
Model
(ECore)
EMF
GMF
M2T
M2T

Annotation-based Approach: Eugenia
§  Hosted in the Epsilon project
§  Kick-starter for developing graphical modeling editors
§  http://www.eclipse.org/epsilon/doc/eugenia/
§  Ecore metamodels are annotated with GCS information
§  From the annotated metamodels, a generator produces GMF
models
§  GMF generators are reused to produce the actual modeling
editors
Be aware:
Application of MDE techniques for
developing MDE tools!

Eugenia Annotations (Excerpt)
§  Diagram
§  For marking the root class of the metamodel that directly or transitively
contains all other classes
§  Represents the modeling canvas
§  Node
§  For marking classes that should be represented by nodes such as rectangles,
circles, …
§  Link
§  For marking references or classes that should be visualized as lines between
two nodes
§  Compartment
§  For marking elements that may be nested in their containers directly
§  Label
§  For marking attributes that should be shown in the diagram representation of
the models

WebModel
@gmf.diagram()
HypertextLayer
@gmf.compartment()
hypertext
1
@gmf.node(
figure="rectangle")
HypertextLayer
001 : WebModel
002 : HypertextLayer
Metamodel with EuGENia annotations
Model fragment in AS Model fragment in GCS
Modeling Canvas
Eugenia Example #1
§  HypertextLayer elements should be directly embeddable in the
modeling canvas that represents WebModels

TutorialList
TutorialDetails
name=“TutorialList“
005 : IndexPage
006 : EntityPage
009 : CLink
target
name=“TutorialDetails“
Metamodel with EuGENia annotations
Model fragment in AS Model fragment in GCS
links
LinkPage
target 1..1
1..*
@gmf.link(
target="target",
style="solid",
target.decoration=
"filledclosedarrow")
links@gmf.node(
label="name",
figure="rectangle")
Eugenia Example #2
§  Pages should be displayed as rectangles and Links should be
represented by a directed arrow between the rectangles

API-based Approach: Graphiti
§ Powerful programming framework for developing
graphical modeling editors
§ Base classes of Graphiti have to be extended to define
concrete syntaxes of modeling languages
§ Pictogram models describe the visualization and the hierarchy of
concrete syntax elements (cf. .gmfgraph models of GMF)
§ Link models establish the mapping between abstract and concrete
syntax elements (cf. .gmfmap models of GMF)
§ DSL on top of Graphiti: Spray

Other Approaches outside Eclipse
MetaEdit+
§  Metamodeling tool outside Eclipse (commerical product)
§  Graphical specification of figures in graphical editor
§  Special tags to specify labels in the figures by querying the models

Other approaches outside Eclipse
Poseidon
§  UML Tool
§  Uses textual syntax to specify mappings, figures, etc.
§  Based on Xtext
§  Provides dedicated concrete syntax text editor

www.mdse-book.com
TEXTUAL CONCRETE
SYNTAX

Textual Modeling Languages
§ Long tradition in software engineering
§ General-purpose programming languages
§ But also a multitude of domain-specific (programming) languages
§  Web engineering: HTML, CSS, Jquery, …
§  Data engineering: SQL, XSLT, XQuery, Schematron, …
§  Build and Deployment: ANT, MAVEN, Rake, Make, …
§ Developers are often used to textual languages
§ Why not using textual concrete syntaxes for modeling
languages?

§  Textual languages defined either as internal or external languages
§  Internal languages
§  Embedded languages in existing host languages
§  Explicit internal languages
§  Becoming mainstream through Ruby and Groovy
§  Implicit internal languages
§  Fluent interfaces simulate languages in Java and C#
§  External languages
§  Have their own custom syntax
§  Own parser to process them
§  Own editor to build sentences
§  Own compiler/interpreter for execution of sentences
§  Many XML-based languages ended up as external languages
§  Not very user-friendly

§  Textual languages have specific strengths compared to graphical
languages
§  Scalability, pretty-printing, …
§  Compact and expressive syntax
§  Productivity for experienced users
§  Guidance by IDE support softens learning curve
§  Configuration management/versioning
§  Concurrent work on a model, especially with a version control system
§  Diff, merge, search, replace, ...
§  But be aware, some conflicts are hard to detect on the text level!
§  Dedicated model versioning systems are emerging!

Concrete Syntaxes in Eclipse
Generic tree-based
EMF Editor
Ecore-based Metamodels
Graphical Concrete Syntax

Every GCS is transformable to a TCS
Example: sWML
Tutorial
presenter:String
title:String
TutorialList
(Tutorial)
Content
Hypertext
ConferenceManagementSystem webapp ConferenceManagementSystem{
hypertext{
index TutorialList shows Tutorial [10] {...}
}
content{
class Tutorial {
att presenter : String;
att title : String;
}
}
}

Anatomy of Modern Text Editors
Error!
Highlighting of
keywords
Code
Completion
Outline View
Error Description

Excursus: Textual Languages in the Past
Basics
§  Extended Backus-Naur-Form (EBNF)
§  Originally introduced by Niklaus Wirth to specify the syntax of Pascal
§  In general, they can be used to specify a context-free grammar
§  ISO Standard
§  Fundamental assumption: A text consists of a sequence of
terminal symbols (visible characters).
§  EBNF specifies all valid terminal symbol sequences using
production rules à grammar
§  Production rules consist of a left side (name of the rule) and a
right side (valid terminal symbol sequences)

Textual Languages
EBNF
§ Production rules consist of
§ Terminal
§ NonTerminal
§ Choice
§ Optional
§ Repetition
§ Grouping
§ Comment
§ …

Textual Languages
Entity DSL
§ Example
type String
type Boolean
entity Conference {
property name : String
property attendees : Person[]
property speakers : Speaker[]
}
entity Person {
}
entity Speaker extends Person {
…
}

Textual Languages
Entity DSL
§ Sequence analysis
type String
type Boolean
entity Conference {
}
entity Person {
}
}
Legend:
§ Keywords
§ Scope borders
§ Separation characters
§ Reference
§ Arbitrary character sequences

Textual Languages
Entity DSL
§ EBNF Grammar
Model := Type*;
Type := SimpleType | Entity;
SimpleType := 'type‘ ID;
Entity := 'entity' ID ('extends' ID)? '{‘ Property* '}‘;
Property := 'property‘ ID ':' ID ('[]')?;
ID := ('a'..'z'|'A'..'Z'|'_') ('a'..'z'|'A'..'Z'|'_'|'0'..'9')*;

Textual Languages
Entity DSL
§ EBNF vs. Ecore
Model := Type*;
Entity := 'entity’ ID ('extends' ID)? '{‘
Property* '}‘;
ID := ('a'..'z'|'A'..'Z'|'_')
('a'..'z'|'A'..'Z'|'_'|'0'..'9')*;

Textual Languages
EBNF vs. Ecore
§  EBNF
+  Specifies concrete syntax
+  Linear order of elements
–  No reusability
–  Only containment relationships
§  Ecore
+  Reusability by inheritance
+  Non-containment and containment references
+  Predefined data types and user-defined enumerations
~  Specifies only abstract syntax
§  Conclusion
§  A meaningful EBNF cannot be generated from a metamodel and vice versa!
§  Challenge
§  How to overcome the gap between these two worlds?

Textual Languages
Solutions
Generic Syntax
§  Like XML for serializing models
§  Advantage: Metamodel is sufficient, i.e., no concrete syntax definition is needed
§  Disadvantage: no syntactic sugar!
§  Protagonists: HUTN and XMI (OMG Standards)
Language-specific Syntax
§  Metamodel First!
§  Step 1: Specify metamodel
§  Step 2: Specify textual syntax
§  For instance: TCS (Eclipse Plug-in)
§  Grammar First!
§  Step 1: Syntax is specified by a grammar (concrete syntax & abstract syntax)
§  Step 2: Metamodel is derived from output of step 1, i.e., the grammar
§  For instance: Xtext (Eclipse Plug-in)
§  Alternative process: take a metamodel and transform it to an intial Xtext grammar!

Xtext
Introduction
§  Xtext is used for developing textual domain specific languages
§  Grammar definition similar to EBNF, but with additional features
inspired by metamodeling
§  Creates metamodel, parser, and editor from grammar definition
§  Editor supports syntax check, highlighting, and code completion
§  Context-sensitive constraints on the grammar described in OCL-like
language

«component»
Parser
«artifact»
Metamodel
«component»
Editor
Xtext
Introduction
oAW
Xtend, ATL
(M2M)
Xpand, Acceleo
(M2C)
Xtext
(TCS)
«artifact»
Grammar
«artifact»
Constraints
«artifact»
Model

Xtext
Grammar
§ Xtext grammar similar to EBNF
§ But extended by
§ Object-oriented concepts
§ Information necessary to derive metamodels and modeling
editors
§ Example
A: (type=B);
A
B
0..1type

Xtext
Grammar
§ Terminal rules
§ Similar to EBNF rules
§ Return value is String by default
§ EBNF expressions
§ Cardinalities
§  ? = One or none; * = Any; + = One or more
§ Character Ranges ‘0’..’9’
§ Wildcard ‘f’.’o’
§ Until Token ‘/*’ -> ‘*/’
§ Negated Token ‘#’ (!’#’)* ‘#’
§ Predefined rules
§ ID, String, Int, URI

Xtext
Grammar
§ Examples
terminal ID :
('^')?('a'..'z'|'A'..'Z'|'_') ('a'..'z'|'A'..'Z'|'_'|'0'..'9')*;
terminal INT returns ecore::EInt :
('0'..'9')+;
terminal ML_COMMENT :
'/*' -> '*/';

Xtext
Grammar
§ Type rules
§ For each type rule a class is generated in the metamodel
§ Class name corresponds to rule name
§ Type rules contain
§ Terminals -> Keywords
§ Assignments -> Attributes or containment references
§ Cross References -> NonContainment references
§ …
§ Assignment Operators
§ = for features with multiplicity 0..1
§ += for features with multiplicity 0..*
§ ?= for Boolean features

Xtext
Grammar
Examples
§ Assignment
State :
'state' name=ID
(transitions+=Transition)*
'end';
§ Cross References
Transition :
event=[Event] '=>' state=[State];

§ Xtext Grammar Definition
Xtext
Tooling
Default Terminals (ID,
STRING,…)
Grammar
Name
Metamodel URI

Xtext
Tooling
§ Xtext Grammar Definition for State Machines

Xtext
Tooling
§ Automatically generated Ecore-based Metamodel

Xtext
Tooling
§ Generated DSL Editor
Error!
Highlighting of
keywords
Code
Completion
(Ctrl+Space)
Outline View
Error
Description

Example #1: Entity DSL
Entity DSL Revisited
type String
type Bool
entity Conference {
}
entity Person {
}
…
}
Model := Type*;
Entity := 'entity‚ ID ('extends' ID)? '{‘
Property* '}‘;
ID := ('a'..'z'|'A'..'Z'|'_')
('a'..'z'|'A'..'Z'|'_'|'0'..'9')*;
Example Model
EBNF Grammar

Example #1
From EBNF to Xtext
Model := Type*;
Entity := 'entity‚ ID
('extends‘ ID)? '{‘
Property*
'}‘;
Property := 'property‘ ID ':'
ID ('[]')?;
ID := ('a'..'z'|'A'..'Z'|'_')
('a'..'z'|'A'..'Z'|'_'|'0'..'9')*;
EBNF Grammar
grammar MyDsl with
org.eclipse.xtext.common.Terminals
generate myDsl "http://MyDsl"
Model : elements+=Type*;
Type: SimpleType | Entity;
SimpleType: 'type' name=ID;
Entity : 'entity' name=ID
('extends‘ extends=[Entity])? '{'
properties+=Property*
'}';
Property: 'property' name=ID ':'
type=[Type] (many?='[]')?;
Xtext Grammar

Example #1
How to specify context sensitive constraints for textual DSLs?
§ Examples
§ Entity names must start with
an Upper Case character
§ Entity names must be
unique
§ Property names must be
unique within one entity
§ Answer
§ Use the same techniques as
for metamodels!
grammar MyDsl with
org.eclipse.xtext.common.Terminals
generate myDsl "http://MyDsl"
Model : elements+=Type*;
Type: SimpleType | Entity;
SimpleType: 'type' name=ID;
Entity : 'entity' name=ID
('extends‘ extends=[Entity])? '{'
properties+=Property*
'}';
Property: 'property' name=ID ':'
type=[Type] (many?='[]')?;
Xtext Grammar

Example #1
How to specify context sensitive constraints for textual DSLs?
§  Examples
1.  Entity names must start with an Upper Case character
2.  Entity names must be unique within one model
3.  Property names must be unique within one entity
§  Solution shown in Check language (similar to OCL)
1.  context myDsl::Entity
WARNING "Name should start with a capital":
name.toFirstUpper() == name;
2.  context myDsl::Entity
ERROR "Name must be unique":
((Model)this.eContainer).elements.name.
select(e|e == this.name).size == 1;
3.  context myDsl::Property
ERROR "Name must be unique":
((Entity)this.eContainer).properties.name.
select(p|p == this.name).size == 1;

Example #1
When to evaluate context sensitive constraints?
§  Every edit operation for cheap constrains
§  Every save operation for cheap to expensive constraints
§  Every generation operation for very expensive constraints

Example #2: Bookshelf (Homework)
n  Edit „Bookshelf“ models in a text-based fashion
n  Given: Example model as well as the metamodel
n  Asked: Grammar, constraints, and editor for Bookshelf DSL

Example #2: Metamodel Details

Example #2: Editor
Give
Warnings!
PageNum > 0

Teaching material for the book
Model-Driven Software Engineering in Practice
by Marco Brambilla, Jordi Cabot, Manuel Wimmer.
Copyright © 2012 Brambilla, Cabot, Wimmer.
www.mdse-book.com
MODEL-DRIVEN SOFTWARE
ENGINEERING IN PRACTICE
Marco Brambilla,
Jordi Cabot,
Manuel Wimmer.
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Model driven software engineering in practice book - chapter 7 - Developing your own modeling language

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Model driven software engineering in practice book - chapter 7 - Developing your own modeling language