代写代考 Week 3: Behind the scenes – the internal structure of a DSML

Week 3: Behind the scenes – the internal structure of a DSML

Session goal
Today, we look behind the scenes of DSML development

– Learn about metamodels and how they are used to represent the structure of languages and models
– Use the metamodel of our turtles language to add additional cool stuff
Style of learning
– Active work: I will introduce a topic, you will try it out on your machines
– Pair work: Two students to share a computer during the active-work sessions
– Prepared work: building on the work you have done in preparation for the session
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What are the three key parts of a language’s definition?
In your own words…
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What technique is used for defining abstract syntax
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Behind the scenes of our language

The metamodel
Let’s look at what Xtext has generated for us
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The metamodel
Let’s look at what Xtext has generated for us
– Need to go to modelling perspective
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The metamodel
Let’s look at what Xtext has generated for us
– Need to go to modelling perspective
– Open the language project and navigate to the
‘model/generated’ folder
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The metamodel
Let’s look at what Xtext has generated for us
– Need to go to modelling perspective
– Open the language project and navigate to the
‘model/generated’ folder
– Right click on the .ecore file and select ‘New/Other…’,
then choose ‘Representations File’
– In the next steps, make sure you initialise from a
‘semantic resource’ and that the ecore file is selected – Choose the ‘Design’ view point
– You’ll now see two items with the name of the .ecore file. Open the one inside the .aird file we have just created and right click on the package that appears.
– Select ‘ /…class diagram’ and confirm the suggested name
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In your pairs
– Open Eclipse
– Open your turtles language
– Explore the generated model
You have 5 minutes
Download last step as tag DSML_v4_scope_tests from the Turtle DSML repository linked from KEATS
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Comparing diagram and grammar
Diagram shows the language metamodel
– The key concepts in the language and their relationships
– Without worrying about how they are represented in text
– Information in any model in our language can be captured as an instance of these classes
Generated from Xtext grammar
– Loosely: every rule becomes a class
– Variable names in rule become attributes / references in the metamodel
– Or-rules become inheritance hierarchies – Mapping can be controlled
– Metamodel (abstract syntax) doesn’t need to be structured the same way as concrete syntax – See more later
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Demo: comparing the metamodel and the grammar

Metamodels
A metamodel is a description of a modelling language
– A model of models
– Defines all concepts that can be used within a language
– A model is constructed using the syntax defined by a metamodel
You know a range of metamodels:
UML class diagrams
UML state machine diagrams Relational data model diagrams …
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Metamodelling
Process of describing new modelling languages
Use meta-models to define modelling languages
Requires meta-language, a language for defining meta-models
– Xtext grammars (a variant of extended Backus–Naur form, EBNF)
– MOF, the OMG meta-object facility
– Essential MOF, EMOF, a more compact form of MOF underlying most of the meta-modelling
languages actually used
– Ecore, the Eclipse Modelling Framework’s variant of EMOF – what we will mostly be using in this
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Models, languages and metalanguages
<> RoomRes RoomNumber:int
<> RoomRes RoomNumber:int
<> RoomRes
<>
<> JRuiocoem:sRtreinsg Meal:string
<>
Juice:string Meal:string
<> CustomerDetails
CustomerID:int
<> CustomerDetails
CustomerID:int
DSML (Metamodel)
Meta- Language
is written in
<> RoomRes
<> Breakfast
Juice:string Meal:string
is written in
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<> RoomRes
RoomNumber:int
<> CustomerDetails
CustomerID:int

The Meta-Object Facility (MOF)
OMG standard for defining modelling languages
– OMG = Object Management Group
– A model of meta-models (a meta-metamodel)
– UML, the OCL, relational database models, specializations of UML can all be represented in the
– Eclipse Modelling Framework (EMF) uses a variant of MOF, called Ecore
An object-oriented approach to defining modelling languages
– Modelling concepts defined as “meta-classes”
– Meta-classes themselves are instances of MOF classes
4 layered architecture to define the modelling / meta-modelling process
– Layers M0 to M3
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Layers M0 and M1
We already know these
Layer M0 is the actual running system
• Instances of executing system elements
• E.g., turtles
• E.g., customer objects, representing actual customers accessing an ecommerce system Layer M1 is a system model
• Defines the types of entities and relationships that make up a system
• E.g., turtle specifications
• E.g., a UML class model, defining a Customer class that specifies that customer objects are
system entities
Every element of M0 is an instance of an element from M1
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Layers M0 and M1
M0: System
title = “Mr” name = “Hyde”
title = “Dr” name = “Jekyll”
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Layers M0 and M1
title : String name : String
M1: Model of a System M0: System
title = “Mr” name = “Hyde”
title = “Dr” name = “Jekyll”
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Layers M0 and M1
title : String name : String
M1: Model of a System M0: System
<>
<>
title = “Mr” name = “Hyde”
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title = “Dr” name = “Jekyll”

Layers M0 and M1
title = “Mr” name = “Hyde”
title = “Dr” name = “Jekyll”
‘:’ and underscore to indicate objects →This is an object diagram
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Layers M0 and M1
No ‘:’ nor underscore to indicate class →This is a class diagram
title : String name : String
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For a modelling tool, all elements of a model are objects
They are on ‘M0’
Their classes are things like ‘Class’, ‘Attribute’, ‘Association’, or ‘MoveCommand’
A meta-model (M2 model) reflects this:
Meta-classes on M2 are instantiated by model elements on M1
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title : String name : String
M1: Model of a System M0: System
<>
<>
title = “Mr” name = “Hyde”
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title = “Dr” name = “Jekyll”

M1: Model of a System
title : String name : String
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M1: Model of a System
:UML Attribute
name = “title” type = “String”
:UML Class
name = “Customer”
:UML Attribute
name = “name” type = “String”
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M2: Meta-model of UML M1: Model of a System
name : String
UML Attribute
*name : String type : String
:UML Attribute
name = “title” type = “String”
:UML Class
name = “Customer”
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Side note: The actual UML meta-model is more complex 18 and uses different names for the meta-classes.
:UML Attribute
name = “name” type = “String”

<>
<>
UML Attribute
*name : String type : String
name : String
M2: Meta-model of UML M1: Model of a System
:UML Class
name = “Customer”
:UML Attribute
name = “title” type = “String”
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Side note: The actual UML meta-model is more complex 18 and uses different names for the meta-classes.
:UML Attribute
name = “name” type = “String”

Instantiation of associations by links. This happens between M1 and M0, too.
<>
<>
UML Attribute
*name : String type : String
M2: Meta-model of UML M1: Model of a System
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Side note: The actual UML meta-model is more complex 18 and uses different names for the meta-classes.
name : String
:UML Attribute
name = “title” type = “String”
:UML Class
name = “Customer”
:UML Attribute
name = “name” type = “String”

M1: Model of a System
31/01/2020 (c) note: The actual UML meta-model is more complex 18 and uses different names for the meta-classes.
:UML Attribute
name = “title” type = “String”
:UML Class
name = “Customer”
:UML Attribute
name = “name” type = “String”
‘:’ and underscore to indicate objects g’s→Coll an object diagram

We use the same trick again
We get a language for defining meta-models A meta-meta-language
• Defines key concepts of meta-models
• Meta-classes and associations of M2 are instances of meta-meta-classes of M3 The MOF / Ecore are really languages for M3 models
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<>
<>
UML Attribute
*name : String type : String
name : String
M2: Meta-model of UML M1: Model of a System
:UML Attribute
name = “title” type = “String”
:UML Class
name = “Customer”
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:UML Attribute
name = “name” type = “String”

M2: Meta-model of UML
UML Attribute
*name : String type : String
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name : String

M2: Meta-model of UML
:EClass src name = “UML Class”
name = “UML Attribute” tgt
:EReference
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name : String
EReference
M3: Ecore Meta-meta-model M2: Meta-model of UML
:EClass src name = “UML Class”
name = “UML Attribute” tgt
:EReference
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name : String
EReference
<>
<>
M3: Ecore Meta-meta-model M2: Meta-model of UML
:EClass src name = “UML Class”
name = “UML Attribute” tgt
:EReference
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Putting It All Together
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M3: Ecore Meta-meta-model
name : String
EReference

Putting It All Together
name : String
EReference
M3: Ecore Meta-meta-model
M2: Meta-model of UML
name = “UML Class”
:EReference
name = “UML Attribute”
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Putting It All Together
name : String
EReference
M3: Ecore Meta-meta-model
M2: Meta-model of UML
name = “UML Class”
:EReference
name = “UML Attribute”
M2: Meta-model of UML
M1: Model of a System
:UML Class
:UML Attribute
name = “title” type = “String”
name = “Customer”
:UML Attribute
name = “name” type = “String”
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Putting It All Together
M3: Ecore Meta-meta-model
M2: Meta-model of UML
name = “UML Class”
:EReference
name = “UML Attribute”
M2: Meta-model of UML
M1: Model of a System
M1: Model of a System
name : String
EReference
:UML Class
:UML Attribute
name = “title” type = “String”
name = “Customer”
:UML Attribute
name = “name” type = “String”
M0: System
title = “Dr” name = “Jekyll”
title = “Mr” name = “Hyde”
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Putting It All Together (2)
M3: Ecore Meta-meta-model
M1: Model of a System
M2: Meta-model of UML
M0: System
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Different kinds of syntax
Abstract syntax Concrete syntax
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Different kinds of syntax Abstract syntax
– What can be talked about in the language
Concrete syntax
– How things are said in the language – What words / pictures
– In what spatial arrangement
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Different kinds of syntax Abstract syntax
– What can be talked about in the language – Captured in the metamodel
Concrete syntax
– How things are said in the language – What words / pictures
– In what spatial arrangement
– Captured in grammar
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Different kinds of syntax Abstract syntax
– What can be talked about in the language – Captured in the metamodel
– One per language
Concrete syntax
– How things are said in the language – What words / pictures
– In what spatial arrangement
– Captured in grammar
– Language can have multiple concrete syntaxes
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Different kinds of syntax Abstract syntax
– What can be talked about in the language
– Captured in the metamodel
– One per language
– Basis for manipulating models
programmatically (see later)
Concrete syntax
– How things are said in the language – What words / pictures
– In what spatial arrangement
– Captured in grammar
– Language can have multiple concrete syntaxes – Basis for editors, file storage, user interaction
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Controlling the shape of the abstract syntax

Controlling the type of attributes and references
Assignment operators in Xtext grammar control what kind of attribute / reference is generated:
Operator Explanation
+= Create variable / reference of type list of right-hand side definition
Can hold multiple instances
statements += Statement+ creates a list of statements in a reference called statement
= Create variable / reference of type of name = ID creates a String-typed attribute name right-hand side definition
Can hold at most one instance
?= Create Boolean attribute public ?= ‘public’ creates a flag that’s true if the Will be true if expression on right hand developer writes the word public
side was matched, false otherwise
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Using return statements to control the metamodel
Grammar rules can return a type
– Determines the type of thing generated into the metamodel
– Useful to restructure the metamodel to something more useful
– Pre-process values
– Remove intermediary unnecessary nodes
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Preprocessing values
Imagine a rule for defining the syntax of real values:
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Preprocessing values
Imagine a rule for defining the syntax of real values:
Instructs Xtext not to ignore any text
→No comments half-way through a REAL value
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Preprocessing values
Imagine a rule for defining the syntax of real values:
This will generate a string attribute in the metamodel
– Every time we access it, we need to parse the value – not efficient We can ask Xtext to generate a float attribute instead:
Instructs Xtext not to ignore any text
→No comments half-way through a REAL value
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Preprocessing values
Imagine a rule for defining the syntax of real values:
Instructs Xtext not to ignore any text
→No comments half-way through a REAL value
This will generate a string attribute in the metamodel
– Every time we access it, we need to parse the value – not efficient We can ask Xtext to generate a float attribute instead:
For this to work, we must import the ecore metamodel, so we can use its definition of EFloat:
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Asks Xtext to use the ecore::EFloat type every time a REAL is used
Text is automatically parsed into a float value.

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