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 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 Common Structure about templates –3 Generated Parts 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 contesto = authors contesto = email abouttemplates –4 e t n o c = t x e l t i t 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 – [<example_of_tag>] ... [/<example_of_tag>] – [<another_example_of_tag> ¼ /] 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 <moduleName>(<MetaModelURI>)/] 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)] ¼ [/template] ● the declaration of a template can include: – overriding properties – pre-conditions : ?(<condition>) – post-treatments : post(<funzione/template>) – inizialization : { <varName>:<type> = <val>; } ● 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)] ¼ [/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 ªgenerateº. [/file] [/template] template && file – example [template public myGenerator(uc : UseCase)] [file (uc.name.concat(©.txt©), false)] These are all the instructions for the script ªgenerateº. [/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 (<iterableExpr>) ] This text will be generated for each element [/for] [for (<iterationVar> : <iteratorType> | <iterableExpr>)] 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)] ¼ <ul> [for (uc.extensionPoint)] <li>[name/]</li> [/for] </ul> ¼ [/file] [/template] for – example ● another implementation : [template public generate(uc : UseCase)] [file (uc.name.concat(©.html©), false)] ¼ <ul> [for ( e : ExtensionPoint | uc.extensionPoint ) ] <li>[name/]</li> <li>[e.name/]</li> [/for] </ul> ¼ [/file] [/template] syntax – if ● the statement if enables conditional generations: [if (<condition>) ] <statements> [else] <statements> [/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)] ¼ [if (uc.extensionPoint->isEmpty())] <p>No Extension Points</p> [/fi] <ul> [for ( e : ExtensionPoint | extensionPoint ) ] <li>[e.name/]</li> [/for] </ul> ¼ [/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 <varName>:<VarType>=<Expression> ] ... [/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 “.mtlºfile ● 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 <query_name>(<receiver_formale> : <type> [, <par_formale> : <type>]) : <ret_type> = invoke(©<percorso_alla_classe>©,©<segantura_metodo>©, Sequence{<receiver_formale>[, <lista_par_formali>]}) /] ● import the query, if defined in some other template [import <template_da_importare> /] 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; } ¼ } 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; } ¼ } [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