Model Driven Engineering : Basic Concepts

Lesson 3 Model to Text Transformations : ACCELEO

Guglielmo De Angelis CNR - IASI / ISTI [email protected]

model transformation

MMM

model transformation MMM M2M

M2T

what is ACCELEO ● it is a framework supporting automatic model transformations – programming language – execution framework – originally developed by Obeo, now in the Eclipse Modeling Framework

● ACCELEO has been designed following MDE principles – enabling the automatic generation of text form a given metamodel (e.g. UML, MOF, EMF)

● available documentation : – Acceleo 3 Web Site

● http://www.eclipse.org/acceleo/ – The Official Documentation

● http://www.eclipse.org/acceleo/documentation/

– The Offical Acceleo Wiki

● http://wiki.eclipse.org/Acceleo about ACCELEO

● ACCELEO is a framework supporting the implementation, and the execution of MODEL 2 TEXT transformations

about ACCELEO

● Acceleo is a framework supporting the implementation, and the execution of MODEL 2 TEXT transformations

Acceleo Transformator (i.e. the program)

Acceleo Execution Engine

about templates – 1

● a template can be seen as a document which it is partially specified – common structure for all the instances of the document – “empty fields” containing istance-specific information ● examples of documents are : – textual documents – models – source codes

about templates – 2

about templates – 3 e s r t u r t a c P u r d t e S t

a n r o e n m e m G o C

definition

● the type of the elements which can be elaborated in each “empty field” of a template is referred context

– all the possible contexts (so all the admissible type of information) depend from the referred metamodel

about templates – 4 s r o h t

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x o

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l t i

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o t s e t n o c

definition

● the type of the elements which can be elaborated in each “empty field” of a template is referred context

– all the possible contexts (so all the admissible type of information) depend from the referred metamodel

● example : – if we consider the metamodel of UML2, the example of context are:

● class, attribute, package, behavior, action

syntax – 1 ● the “empty fields” represents the variable part of a template

● they are “filled” by script areas which can emit text, according to both the context they are executed, and the given input model

● any script area is marked by means of specific tags – [] ... [/] – [ … /]

syntax – 2 ● the acceleo programming language forseen also “comment area” : [comment ... /]

● la direttiva module, definisce il modulo Acceleo che si sta implementando ed il tipo di linguaggio dei modelli in ingresso – il metamodello può essere considerato la grammatica sulla quale sono basati i modelli oggetto della trasformazione [module ()/]

example ● refer in an ACCELEO program the UML 2.0 metamodel – URI: http://www.eclipse.org/uml2/3.0.0/UML

[module myGenerate('http://www.eclipse.org/uml2/3.0.0/UML') /]

syntax – template

● the statement template declares a trasformator and it defines the elements that will match [template public myGenerator(instance : myType)] … [/template]

● the declaration of a template can include: – overriding properties – pre-conditions : ?() – post-treatments : post() – inizialization : { : = ; } ● myType is the type of the parsed instance that matching will activate the script (Package, Class, Properties, …)

● templates can be called each-other – please always think to templates as “functions”, and design them with modularity

syntax – file

● the statement file declares on which file the emitted text will be redirected [template public myGenerator(instance : myType)/] [file(fileName, appendMode, charEncoding)] … [/file] [/template]

● fileName is the file that will be created during the execution ( the ext. must be given)

● appendMode and charEncoding are optional parameters

template && file – example

[template public myGenerator(uc : UseCase)] [file (uc.name.concat('.txt'), false)] These are all the instructions for the script “generate”. [/file] [/template]

template && file – example

[template public myGenerator(uc : UseCase)] [file (uc.name.concat('.txt'), false)] These are all the instructions for the script “generate”. [/file] [/template]

● the attributes of an element are accessed like in most of the object- oriented notations

● but, some conditional expression will use the syntaxt “->” (see the following example on the IF statement) – the reason is that such expression are not attributes, but functions in the OCL constraint language

context

[template public generate(uc : UseCase)] * Explicit Reference @ Name : [uc.name/] Implicit Reference @ Name : [name/] [/template]

● the “context” is given by the element of the metamodel (i.e. a type) that is considered for that specifc portion of code

● the “context” subsumes the visibility of the functionalities and the properties that are accessible

● it is possible to refer properties both explicitely or implicetely

syntax – for ● the for statement defines loops on the matching modelied elements

● usage:

[for () ] This text will be generated for each element [/for]

[for ( : | )] This text will be generated for each element [/for]

● it defines an implicit context-switch

for – example ● ... for any use case in the input model generate a list (e.g. HTML list item tag) with the names of all the contained extension point [template public generate(uc : UseCase)] [file (uc.name.concat('.html'), false)] …

[name/]

… [/file] [/template]

for – example

● another implementation :

[template public generate(uc : UseCase)] [file (uc.name.concat('.html'), false)] …

[name/]
[e.name/]

… [/file] [/template]

syntax – if ● the statement if enables conditional generations: [if () ] [else] [/if]

● where condition is a boolean

● admissible operators are : – = , <> , < , <= , > , >= , or , and , not ● operands: values, objects, call to scripts, call to services, links to metamodels

if – example [template public generate(uc : UseCase)] [file (uc.name.concat('.html'), false)] … [if (uc.extensionPoint>isEmpty())]

No Extension Points

[/fi]

[e.name/]

… [/file] [/template]

syntax – let ● ACCELEO in mostly declarative!!! Nevertheless ...

syntax – let ● the statement let stores the result of an expression within a local variable

● a local variable is accessible only within the scope of its declaration block

● a local variable CANNOT have modified its value after the initialization

[let := ] ... [/let]

ACCELEO services : advanced features ● the ACCELEO services are primitives which extend the minimal (default) language – typically they implements functionalities which are difficult to be directly coded within a “.mtl”file ● two type of services: – native services offered by the ACCELEO platform

● among the others services for the OCL support – services developed by the user of the platform

● coded directly in Java ● basically, a service is a(ny) public method offered by a Java class ● the Java classes providing services must be – imported within the templates – integrated with the generator ACCELEO services – example ● the service indexOf : – it can be applied to a sting R ( i.e. the input ) – it takes a string S as parameter – it returns the position of the first occurrence of S in R ● its signature in a Java class would be : public int indexOf (String R, String S)

● defining a service by means of a Java class: – the first parameter of (public) method is the receiver of the service

● the receiver defines the type of the objects where that service can be applied – the other parameters of the (public) method are the (ordered) parameters of the service – the return type of the (public) method matches with the type returned by the service

ACCELEO services : how to ● how to define/import services in ACCELEO? – this part is well explained in several tutorials: – http://wiki.eclipse.org/Acceleo/Getting_Started – receipt “I want see what happens under the hood”:

● implement a Java class ● implement the public method offering the service – ATTENTION!!: remember the convention about the receiver ● link the service in Java to an ACCELEO query

[query public ( : [, : ]) : = invoke('','', Sequence{[, ]}) /]

● import the query, if defined in some other template [import /] ACCELEO services – example 1 ● write an ACCELEO service which sets to capital the first caracther of a string

ACCELEO services – example 1.1 public class MyService { public String firstUpper(String s){ if (s.length() > 0) s = Character.toUpperCase(s.charAt(0)) + s.substring(1); return s; } … }

ACCELEO services – example 1.2 public class MyService { public String firstUpper(String s){ if (s.length() > 0) s = Character.toUpperCase(s.charAt(0)) + s.substring(1); return s; } … } [query public acceleoFirstUpper (rec : String) : String = invoke('MyService', 'firstUpper(java.lang.String)', Sequence{'rec'}) /]

ACCELEO services – example 2

● write an ACCELEO service which counts the occurrences of a given char (as integer in ASCII) in an input string.

ACCELEO services – example 2.1 public class MyService { public int count(String str, int asciiCodeCar){ int counter=0; char c = (char) asciiCodeCar; for (int i=0; i < str.length(); i++) if (str.charAt(i) == c) counter++; return counter; } }

ACCELEO services – example 2.2 public class MyService { public int count(String str, int asciiCodeCar){ int counter=0; char c = (char) asciiCodeCar; for (int i=0; i < str.length(); i++) if (str.charAt(i) == c) counter++; return counter; } } [ query public acceleoCount (rec:String,code:Integer): Integer = invoke('MyService','count(java.lang.String,int)', Sequence{'rec','code'}) /]

basic biblio

● Marco Brambilla, Jordi Cabot, Manuel Wimmer : Model-Driven Software Engineering in Practice. Synthesis Lectures on Software Engineering, Morgan & Claypool Publishers (2012)

● J. Arlow, I. Neustadt: “UML2 e Unified Process - analisi e progettazione Object-Oriented”, 2a Ed., McgrawHill. 2007

● Acceleo

– The Official Documentation

● http://www.eclipse.org/acceleo/documentation/ – The Offical Acceleo Wiki

● http://wiki.eclipse.org/Acceleo – Acceleo 3 Web Site

● http://www.eclipse.org/acceleo/