Overcoming the
Impedance Mismatch
Between Source Code
and Architecture
Peter Friese, itemis
@peterfriese
@xtext
(c) 2009 Peter Friese. Distributed under the EDL V1.0 - http://www.eclipse.org/org/documents/edl-v10.php
More info: http://www.peterfriese.de / http://www.itemis.com

Peter Friese, itemis
@peterfriese
@xtext
(c) 2009 Peter Friese. Distributed under the EDL V1.0 - http://www.eclipse.org/org/documents/edl-v10.php
More info: http://www.peterfriese.de / http://www.itemis.com

Stop drawing useless
diagrams
and writing boring code
Peter Friese, itemis
@peterfriese
@xtext
(c) 2009 Peter Friese. Distributed under the EDL V1.0 - http://www.eclipse.org/org/documents/edl-v10.php
More info: http://www.peterfriese.de / http://www.itemis.com

UML - One Language To Rule Them All
http://en.wikipedia.org/wiki/File:UML_Diagrams.jpg

UML doesn’t cut it!

Increasing Gap

od els
M
Code
Increasing Gap

(UML) Models = Shelfware
http://www.flickr.com/photos/misterdna/49841409/

Solution:
Two-Way Tools

Result: Bloated Diagrams No-one can understand
Person SomeOtherMeaninglessClass
User Author Administrator Librarian SomeOtherMeaninglessClass
SomeOtherMeaninglessClass
Library Fee
Book Page
SomeOtherMeaninglessClass
Shelf Folder
SomeOtherMeaninglessClass
SomeOtherMeaninglessClass SomeOtherMeaninglessClass SomeOtherMeaninglessClass

Solution: Semantic Diagrams
<<EntityBean>>
Book
title: String
isbn: String

Instead of being a
solution...

... two-way tools
have proven to be
a dead-end
http://www.flickr.com/photos/cgommel/561929101/

... two-way tools
have proven to be
a dead-end
http://www.flickr.com/photos/cgommel/561929101/

Let’s step back

What are the real problems?

Boring code

Accidental complexity

Wrong level of abstraction

Anatomy of Modern Software
Software artifact

Anatomy of Modern Software
manually written code Frameworks
Libraries

Anatomy of Modern Software
manually written
code
Frameworks
schematic code (manually written)
Libraries

(Rote) coding doesn’t cut it either!

(Rote) coding doesn’t cut it either!

Problems

Problems

Problems
Can we solve them with models?

Yes, we can!

Code Generation Helps
Model
manually written
code
Generator
Frameworks
schematic code (generated)
Libraries

MDSD
Metamodel
<<instanceof>>
generated manually written
Model Model
code code
Generator
Platform

MDSD with UML
Metamodel
<<instanceof>>
generated manually written
Model Model
code code
Generator
UML Platform

UML and MDSD

A Marriage Made in Heaven?

Not.

UML and MDSD

UML and MDSD
⊕ Existing tools

UML and MDSD
⊕ Existing tools
⊕ Good overview

UML and MDSD
⊕ Existing tools
⊕ Good overview
⊕ Graphical - managers / clients like that

UML and MDSD
⊕ Existing tools
⊕ Good overview
⊕ Graphical - managers / clients like that
⊖ complex meta model

UML and MDSD
⊕ Existing tools
⊕ Good overview
⊕ Graphical - managers / clients like that
⊖ complex meta model
⊖ teamwork challenging at best

UML and MDSD
⊕ Existing tools
⊕ Good overview
⊕ Graphical - managers / clients like that
⊖ complex meta model
⊖ teamwork challenging at best
⊖ model evolution problematic

UML and MDSD
⊕ Existing tools
⊕ Good overview
⊕ Graphical - managers / clients like that
⊖ complex meta model
⊖ teamwork challenging at best
⊖ model evolution problematic
⊖ UML is too generic, it’s not a DSL

UML and MDSD
⊕ Existing tools
⊕ Good overview
⊕ Graphical - managers / clients like that
⊖ complex meta model
⊖ teamwork challenging at best
⊖ model evolution problematic
⊖ UML is too generic, it’s not a DSL
⊖ UML profiles don’t help either

UML and MDSD
⊕ Existing tools
⊕ Good overview
⊕ Graphical - managers / clients like that
⊖ complex meta model
⊖ teamwork challenging at best
⊖ model evolution problematic
⊖ UML is too generic, it’s not a DSL
⊖ UML profiles don’t help either
⊖ tools not integrated in IDE

UML and MDSD
⊕ Existing tools
⊕ Good overview
⊕ Graphical - managers / clients like that
⊖ complex meta model
⊖ teamwork challenging at best
⊖ model evolution problematic
⊖ UML is too generic, it’s not a DSL
⊖ UML profiles don’t help either
⊖ tools not integrated in IDE
⊖ long round trips

UML and MDSD
⊕ Existing tools
⊕ Good overview
⊕ Graphical - managers / clients like that
⊖ complex meta model
⊖ teamwork challenging at best
⊖ model evolution problematic
⊖ UML is too generic, it’s not a DSL
⊖ UML profiles don’t help either
⊖ tools not integrated in IDE
⊖ long round trips
⊖ developers don’t like diagrams that much

UML doesn’t cut it!

Looking at the drawbacks...

UML and MDSD
⊕ Existing tools
⊕ Good overview
⊕ Graphical - managers / clients like that
⊖ complex meta model
⊖ teamwork challenging at best
⊖ model evolution problematic
⊖ UML is too generic, it’s not a DSL
⊖ UML profiles don’t help either
⊖ tools not integrated in IDE
⊖ long round trips
⊖ developers don’t like diagrams that much

UML and MDSD
⊖ complex meta model
⊖ teamwork challenging at best
⊖ model evolution problematic
⊖ UML is too generic, it’s not a DSL
⊖ UML profiles don’t help either
⊖ tools not integrated in IDE
⊖ long round trips
⊖ developers don’t like diagrams that much

UML and MDSD
⊖ complex meta model
⊖ teamwork challenging at best
⊖ model evolution problematic
⊖ UML is too generic, it’s not a DSL
⊖ UML profiles don’t help either
⊖ tools not integrated in IDE
⊖ long round trips
⊖ developers don’t like diagrams that much

... these are promises of DSLs!

What are DSLs?

Suppose...

You’d want to core an apple...

... for your kids.

?
Right tool for the job?

Your trusty swiss army knife!

You can use it for other stuff, too.
E.g., opening a bottle of wine.

Suppose...

You’d want to core a few more apples...

... for an apple cake.

Still the best tool for the job?

Better use this one.

and this one:

BUT
avoid the unitasker!

BUT
avoid the unitasker!

A DSL is...

A specific tool
for a specific job

A specific tool
for a specific job

DSL Samples

select name, salary
from employees
where salary > 2000
order by salary

<project name="MyProject" default="dist" basedir=".">
<property name="src" location="src"/>
<property name="build" location="build"/>
<property name="dist" location="dist"/>
<target name="init">
<mkdir dir="${build}"/>
</target>
<target name="compile" depends="init">
<javac srcdir="${src}" destdir="${build}"/>
</target>
<target name="dist" depends="compile">
<mkdir dir="${dist}/lib"/>
<jar jarfile="${dist}/lib/MyProject.jar"
basedir="${build}"/>
</target>
<target name="clean">
<delete dir="${build}"/>
<delete dir="${dist}"/>
</target>
</project>

<project name="MyProject" default="dist" basedir=".">
<property name="src" location="src"/>
<property name="build" location="build"/>
<property name="dist" location="dist"/>
<target name="init">
<mkdir dir="${build}"/>
</target>
<target name="compile" depends="init">
<javac srcdir="${src}" destdir="${build}"/>
</target>
<target name="dist" depends="compile">
<mkdir dir="${dist}/lib"/>
<jar jarfile="${dist}/lib/MyProject.jar"
basedir="${build}"/>
</target>
<target name="clean">
<delete dir="${build}"/>
<delete dir="${dist}"/>
</target>
</project>

DSL Advantages

DSL Advantages
⊕ Focussed

DSL Advantages
⊕ Focussed
⊕ Precise metamodel, perfect fit

DSL Advantages
⊕ Focussed
⊕ Precise metamodel, perfect fit
⊕ No misuse / mismodeling (thanks to

DSL Advantages
⊕ Focussed
⊕ Precise metamodel, perfect fit
⊕ No misuse / mismodeling (thanks to
constrained meta model)

DSL Advantages
⊕ Focussed
⊕ Precise metamodel, perfect fit
⊕ No misuse / mismodeling (thanks to
constrained meta model)
⊕ diff / merge possible

DSL Advantages
⊕ Focussed
⊕ Precise metamodel, perfect fit
⊕ No misuse / mismodeling (thanks to
constrained meta model)
⊕ diff / merge possible
⊕ teamwork possible

DSL Advantages
⊕ Focussed
⊕ Precise metamodel, perfect fit
⊕ No misuse / mismodeling (thanks to
constrained meta model)
⊕ diff / merge possible
⊕ teamwork possible
⊕ developers like text

DSL Advantages
⊕ Focussed
⊕ Precise metamodel, perfect fit
⊕ No misuse / mismodeling (thanks to
constrained meta model)
⊕ diff / merge possible
⊕ teamwork possible
⊕ developers like text
⊖ need to build your own tools

DSL Disadvantages
⊕ Focussed
⊕ Precise metamodel, perfect fit
⊕ No misuse / mismodeling (thanks to
constrained meta model)
⊕ diff / merge possible
⊕ teamwork possible
⊕ developers like text
⊖ need to build your own tools

1)Create ANTLR grammar
2)Generate lexer / parser
3)Parser will create parse tree
4)Transform parse tree to semantic model
5)Iterate model
6)Pass model element(s) to template

DSLs are...

Flexible

Adaptable

Complicated

Expensive

- A DSL for Writing DSLs

Underlying Technology

Model
G
ra
m
m
ar

ar
Model
m
m
ra
G
Generator

ar
Model
m
m
ra
G
Generator
Runtime
Superclass
Subclass Class
LL(*) Parser ECore meta model Editor

ar
Model
m
m
ra
G
Generator
Runtime
Superclass
Subclass Class
LL(*) Parser ECore meta model Editor

Grammar (similar to EBNF)
grammar org.xtext.example.Entity with org.eclipse.xtext.common.Terminals
generate entity "http://www.xtext.org/example/Entity"
Model:
(types+=Type)*;
Type:
TypeDef | Entity;
TypeDef:
"typedef" name=ID ("mapsto" mappedType=JAVAID)?;
JAVAID:
name=ID("." ID)*;
Entity:
"entity" name=ID ("extends" superEntity=[Entity])?
"{"
(attributes+=Attribute)*
"}";
Attribute:
type=[Type] (many?="*")? name=ID;

grammar org.xtext.example.Entity
with org.eclipse.xtext.common.Terminals Meta model inference
generate entity
"http://www.xtext.org/example/Entity"
entity
Model:
(types+=Type)*;
Model
Type:
TypeDef | Entity;
types
TypeDef: *
Type
"typedef" name=ID
name: EString
("mapsto" mappedType=JAVAID)?;
superEntity
JAVAID:
name=ID("." ID)*; TypeDef Entity
Entity: mappedType attributes
"entity" name=ID
Attribute
("extends" superEntity=[Entity])? JAVAID
name: EString
"{" name: EString
many: EBoolean
(attributes+=Attribute)*
"}"; type
Attribute:
type=[Type] (many?="*")? name=ID;

grammar org.xtext.example.Entity
with org.eclipse.xtext.common.Terminals Meta model inference
generate entity
"http://www.xtext.org/example/Entity"
entity Rules -> Classes
Model:
(types+=Type)*;
Model
Type:
TypeDef | Entity;
types
TypeDef: *
Type
"typedef" name=ID
name: EString
("mapsto" mappedType=JAVAID)?;
superEntity
JAVAID:
name=ID("." ID)*; TypeDef Entity
Entity: mappedType attributes
"entity" name=ID
Attribute
("extends" superEntity=[Entity])? JAVAID
name: EString
"{" name: EString
many: EBoolean
(attributes+=Attribute)*
"}"; type
Attribute:
type=[Type] (many?="*")? name=ID;

grammar org.xtext.example.Entity
with org.eclipse.xtext.common.Terminals Meta model inference
generate entity
"http://www.xtext.org/example/Entity"
entity
Model:
(types+=Type)*;
Model
Type:
TypeDef | Entity;
types
TypeDef: *
Type
"typedef" name=ID
name: EString
("mapsto" mappedType=JAVAID)?;
superEntity
JAVAID:
name=ID("." ID)*; TypeDef Entity
Entity: mappedType attributes
"entity" name=ID
Attribute
("extends" superEntity=[Entity])? JAVAID
name: EString
"{" name: EString
many: EBoolean
(attributes+=Attribute)*
"}"; type
Attribute:
type=[Type] (many?="*")? name=ID;

grammar org.xtext.example.Entity
with org.eclipse.xtext.common.Terminals Meta model inference
generate entity
"http://www.xtext.org/example/Entity"
entity Alternatives -> Hierarchy
Model:
(types+=Type)*;
Model
Type:
TypeDef | Entity;
types
TypeDef: *
Type
"typedef" name=ID
name: EString
("mapsto" mappedType=JAVAID)?;
superEntity
JAVAID:
name=ID("." ID)*; TypeDef Entity
Entity: mappedType attributes
"entity" name=ID
Attribute
("extends" superEntity=[Entity])? JAVAID
name: EString
"{" name: EString
many: EBoolean
(attributes+=Attribute)*
"}"; type
Attribute:
type=[Type] (many?="*")? name=ID;

grammar org.xtext.example.Entity
with org.eclipse.xtext.common.Terminals Meta model inference
generate entity
"http://www.xtext.org/example/Entity"
entity
Model:
(types+=Type)*;
Model
Type:
TypeDef | Entity;
types
TypeDef: *
Type
"typedef" name=ID
name: EString
("mapsto" mappedType=JAVAID)?;
superEntity
JAVAID:
name=ID("." ID)*; TypeDef Entity
Entity: mappedType attributes
"entity" name=ID
Attribute
("extends" superEntity=[Entity])? JAVAID
name: EString
"{" name: EString
many: EBoolean
(attributes+=Attribute)*
"}"; type
Attribute:
type=[Type] (many?="*")? name=ID;

grammar org.xtext.example.Entity
with org.eclipse.xtext.common.Terminals Meta model inference
generate entity
"http://www.xtext.org/example/Entity"
entity Assignment -> Feature
Model:
(types+=Type)*;
Model
Type:
TypeDef | Entity;
types
TypeDef: *
Type
"typedef" name=ID
name: EString
("mapsto" mappedType=JAVAID)?;
superEntity
JAVAID:
name=ID("." ID)*; TypeDef Entity
Entity: mappedType attributes
"entity" name=ID
Attribute
("extends" superEntity=[Entity])? JAVAID
name: EString
"{" name: EString
many: EBoolean
(attributes+=Attribute)*
"}"; type
Attribute:
type=[Type] (many?="*")? name=ID;

grammar org.xtext.example.Entity
with org.eclipse.xtext.common.Terminals Meta model inference
generate entity
"http://www.xtext.org/example/Entity"
entity
Model:
(types+=Type)*;
Model
Type:
TypeDef | Entity;
types
TypeDef: *
Type
"typedef" name=ID
name: EString
("mapsto" mappedType=JAVAID)?;
superEntity
JAVAID:
name=ID("." ID)*; TypeDef Entity
Entity: mappedType attributes
"entity" name=ID
Attribute
("extends" superEntity=[Entity])? JAVAID
name: EString
"{" name: EString
many: EBoolean
(attributes+=Attribute)*
"}"; type
Attribute:
type=[Type] (many?="*")? name=ID;

ar
Model
m
m
ra
G
Generator Fragments
Generator
Runtime
Superclass
Subclass Class
LL(*) Parser ecore meta model editor

ar
Model
m
m
ra
G
Generator
Runtime
Google Guice
Superclass
Subclass Class
LL(*) Parser ecore meta model editor

Demo

@SuppressWarnings("serial")
@Entity
@Table(name = "CUSTOMER_INFO")
public class CustomerInfo implements Serializable {
@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "idSeq")
@SequenceGenerator(name = "idSeq", sequenceName = "CUST_SEQ", allocationSize = 1)
@Column(name = "CUST_ID", nullable = false)
private String customerId;
public void setCustomerId(String customerId) {
this.customerId = customerId;
}
public String getCustomerId() {
return customerId;
}
@Column(name = "EMAIL", nullable = false, length = 128)
private String emailAddress;
public String getEmailAddress() {
return emailAddress;
}
public void setEmailAddress(String emailAddress) {
String oldValue = emailAddress;
this.emailAddress = emailAddress;
firePropertyChangedEvent("emailAddress", oldValue, this.emailAddress);
}

@SuppressWarnings("serial")
@Entity
@Table(name = "CUSTOMER_INFO")
public class CustomerInfo implements Serializable {
@Id
@GeneratedValue(strategy = GenerationType.SEQUENCE, generator = "idSeq")
@SequenceGenerator(name = "idSeq", sequenceName = "CUST_SEQ", allocationSize = 1)
@Column(name = "CUST_ID", nullable = false)
private String customerId;
public void setCustomerId(String customerId) {
this.customerId = customerId;
}
public String getCustomerId() {
return customerId;
}
@Column(name = "EMAIL", nullable = false, length = 128)
private String emailAddress;
public String getEmailAddress() {
return emailAddress;
}
public void setEmailAddress(String emailAddress) {
String oldValue = emailAddress;
this.emailAddress = emailAddress;
firePropertyChangedEvent("emailAddress", oldValue, this.emailAddress);
}

entity CustomerInfo
(id=CUST_ID, sequenceName=CUST_SEQ)
{
String emailAddress (notNull, length = 128)
}

entity CustomerInfo
(id=CUST_ID, sequenceName=CUST_SEQ)
{
String emailAddress (notNull, length = 128)
}
Bean
DAO
(POJO)

Do DSLs cut it?

Yes, they do

Yes, they do

Yes, they do

Yes, they do

Concentrate on
Essentials

Higher Efficiency

Better Maintainability

No More Boring Code

A New Babylonic
Plethora of Languages?

DSLs will improve
communication in projects

Committers
Heiko Sven Moritz Peter Dennis Jan Patrick Sebastian Michael Knut
Behrens Efftinge Eysholdt Friese Hübner Köhnlein Schönbach Zarnekow Clay Wannheden
Individual