Bridging existing Web Modeling Languages to Model-Driven Engineering: A Metamodel for WebML Andrea Schauerhuber, Manuel Wimmer, Elisabeth Kapsammer Workshop

Bridging existing Web Modeling Languages to Model-Driven Engineering:A Metamodel for WebMLAndrea Schauerhuber, Manuel Wimmer, Elisabeth Kapsammer

Workshop on Model-Driven Web Engineering (MDWE’06) in conj. with ICWE’06Tuesday, July 11, 2006Standford Linear Accelerator Center, Palo Alto, California

Andrea SchauerhuberWomen’s Postgraduate College for Internet TechnologiesInstitute of Software Technology and Interactive Systems

Vienna University of Technologyhttp://wit.tuwien.ac.at

2

Outline

Motivation Related Work Methodology & Conceptual Architecture Automatic Metamodel Generation Manual Refactorings Lessons Learned Outlook

3

Motivation

Most existing Web modeling languages not fully model-driven, i.e., they often provide code

generation facilities, only but no model transformation or a common format for

model exchange Metamodels or UML Profiles are a prerequisite for

model-driven engineering WebML is a prominent Web modeling language,

due to existing tool support (WebRatio) and applications in real world projects

WebML is not specified in terms of a metamodel but in terms of a DTD

A Metamodel for WebML

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Related Work

A metamodel for WebML proposed by [Moreno et al., 2006]Why yet another metamodel for WebML?Developed in parallel, but … different goals: DSL vs. UML Profile different methodology:

bottom-up vs. top-down semi-automatic vs. manual

different application: transformation of existing WebML XML documents to

models vs. models from scratch Metamodels for other Web modeling languages

UWE [Koch et al., 2003], W2000 [Baresi et al., 2006], Netsilon [Muller et al., 2005] are based on MOF 1.4

We use new technologies (MOF 2.0, EMF, Ecore, ATL, oaW)

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Methodology

Define WebML metamodel semi-automatically

What WebML to use?

WebRatio DTD: used as a basis for automatic generation of a first version of the metamodel

WebRatio functionality: used to manually incorporate concepts that could not be captured by the DTD

WebML literature: used to manually refine the generated metamodel

Step 1

Step 2

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M2

M1

WebML Metamodel

«conformsTo»

«conformsTo»

WebML Model

WebML DTD

WebML XML Doc

Class

Class Class Class

Class

Class Class

Class

Class Class Class

Class

Class Class Class

Class

Class Class

Class

Class Class

Class

Class Class Class

Class

Class Class

Class

Class Class Class

Class

Class Class Class

Class

Class Class

Class

Class Class<!ELEMENT A><!ATTLIST A>

<!ELEMENT B><!ATTLIST B>

<!ELEMENT C><!ATTLIST C>

M3 Mapping

«conformsTo»

«conformsTo»

MOFDTD-Grammar

The Conceptual Architecture

«uses»

«parses» «generates»

MetaModelGenerator (MMG)

«parses» «generates»

<!ELEMENT A><!ATTLIST A>



XMI-Serializer<ecore class>

<ecore><ecore class><ecore att>

Omondo

Draft Metamodel

MetaModelGenerator (MMG)

User

DTD element type object

graph

Metamodel element object

graphDTD-Parser Transformer

«uses» «uses»

2.

Semanticenrichment

1.

TransformationRules Heuristics

Mapping

<!ELEMENT A><!ATTLIST A>



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Step 1: Automatic Metamodel Generation

XML technical space Model technical space Various approaches examined [Wimmer et al., 2006] DTD, XML Schema vs. UML, ER, ORM Until now no approach to generate MOF-based

metamodels from DTDs Based on these approaches we developed

Set of Transformation Rules Rules for transforming XMLElementTypes Rules for transforming XMLAttributes

3 Heuristics (may not be applicable for all DTDs) IDREF(S) Resolution Boolean Identification Package Identification

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*

ENTITYENTITY

RELATIONSHIPRELATIONSHIP

relationship<!ELEMENT RELATIONSHIP EMPTY>

entity 1

Step 1: Automatic Metamodel Generation

<!ATTLIST RELATIONSHIPname CDATA #IMPLIEDentity IDREF #REQUIRED>

<!ATTLIST ENTITYid ID #REQUIREDname CDATA #IMPLIED>

id:EStringid:EStringname:EString[0..1]name:EString[0..1]

name:EString[0..1]name:EString[0..1]entity:EObjectentity:EObject

An Example for Transformation Rules & Heuristics

DTD Metamodel

1) Create classes for XML element types2) Create containment references for XML

content particles3) Create attributes for XML attributes

1) Apply Heuristic IDREF Resolution

<!ELEMENT ENTITY (RELATIONSHIP*)><!ELEMENT ENTITY (RELATIONSHIP*)>ENTITY

<!ATTLIST ENTITYid ID #REQUIREDname CDATA #IMPLIED>

<!ATTLIST RELATIONSHIPname CDATA #IMPLIEDentity IDREF #REQUIRED>entity

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Step1: Output - Metamodel Metrics

Automatically generated metamodel draft

EPackage 3

EClass 54

EAttribute 143

EBoolean 37

EInteger 0

EString 93

IDREF unresolved 12

EEnumeration 13

EReference 125

Containment 105

IDREF resolved 20

EEnumeration 13

EEnumLiteral 93

Superclasses 0

Subclasses 0

MAX EClasses/EPackage 49

MIN EClasses/EPackage 5

AVG EClasses/EPackage 27Metamodel metrics, [Ma et al., 2004]

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Step 2: Manual Refactoring

DTD deficienciesUnknown referenced element type(s)Missing role conceptAwkward cardinalitiesXOR constraintsNo explicit grouping mechanismMissing inheritance conceptLimited set of datatypesNo bi-directional associations

Manual Refactorings necessary

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Step 2: Manual Refactoring – Example 1

It is not possible to identify which element type(s) may be referenced from an IDREF-typed attribute

<!ELEMENT Link (…)>

<!ATTLIST Linktype (normal|automatic|transport) ‘normal’to IDREF #REQUIRED…>

<!ELEMENT IndexUnit (…, LINK*,…)>

Unknown Referenced Element Type(s)

Linktype:LinkType

EObjectto

1IndexUnitDataUnit

…

LinkableElement

link*

link*

link*

link*

<!ELEMENT Link (…)>

type (normal|automatic|transport) ‘normal’to IDREF #REQUIRED

<!ELEMENT IndexUnit (…, LINK*,…)>

to 1

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DTDs do not allow to express that an element type can be deployed in different contexts

<!ELEMENT ConnectUnit(SourceSelector?,TargetSelector?,…)>

<!ELEMENT Selector(SelectorCondition+)>

<!ELEMENT SourceSelector (SelectorCondition+)>

<!ELEMENT TargetSelector (SelectorCondition+)>

Missing Role Concept

0..1

0..1targetSelector

sourceSelectorConnectUnit

SourceSelector

TargetSelector

Selector

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Restricted mechanism of DTDs to specify cardinalities (e.g., 2..5)

<!ELEMENT AlternativePage (Page, Page+)><!ATTLIST AlternativePage …defaultPage IDREF #IMPLIED>

Awkward Cardinalities

page

defaultPage 0..1

1

page

PageAlternative

Page

1..*

page2..*

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DTDs provide no mechanism to express xor-constraints

<!ELEMENT Area (…,Area*,Page*,…)><!ATTLIST Area…defaultPage IDREF #IMPLIEDdefaultArea IDREF #IMPLIED…>

Missing XOR Constraints

defaultPage0..1

*page

0..1

defaultArea

* area

PageArea

{xor}

XOR

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No Explicit Grouping Mechanism



<!ENTITY % StructureDTD SYSTEM "Structure.dtd">

%StructureDTD;

<!ENTITY % NavigationDTD SYSTEM “Navigation.dtd">

%NavigationDTD;

WebML

<!ELEMENT Entity (…)><!ELEMENT Attribute EMPTY>…

<!ELEMENT Link (…)>…

Structure

NavigationContent

Management

Access Control

HypertextOrganization

Hypertext

Content

<!ENTITY % StructureDTD SYSTEM "Structure.dtd">

%StructureDTD;

<!ENTITY % NavigationDTD SYSTEM “Navigation.dtd">

%NavigationDTD;

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Missing Inheritance Concept

to

1

link *LinkableElement

ContentUnit

Link

GetUnitEntryUnitDisplayUnit

SortableUnit DataUnit

HierarchicalIndexUnit

MultiChoiceIndexUnit IndexUnit

MultiDataUnit

ScrollerUnit

Hypertext1)

- normal- transport- automatic

«enumeration» LinkType

type:LinkType

ContentManagement1)

1 relationship1 entity

selector0..1

0..10..1

0..1targetselector

sourceselectorselector

to

to

*

*

0..1

0..1

okLink

koLink

OperationUnit

SetUnit ContentManagementUnit

RelationshipManagementUnit

ConnectUnit DisconnectUnit

Content::Relationship

DeleteUnitModifyUnitCreateUnit

Content::Entity

Hypertext::Selector

OKLink

KOLink

Hypertext::LinkableElement

EntityManagementUnit

1) Please note, that this is only an excerpt from the metamodel. See http://www.big.tuwien.ac.at/projects/webml/index.html for the full specification.

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Step2: Output - Metamodel Metrics

Automatically generated metamodel draft

Refactored metamodel

EPackage 3 6

EClass 54 54

EAttribute 143 84

EBoolean 37 25

EInteger 0 2

EString 93 44

IDREF unresolved 12 0

EEnumeration 13 13

EReference 125 74

Containment 105 48

IDREF resolved 20 26

EEnumeration 13 8

EEnumLiteral 93 40

Superclasses 0 9

Subclasses 0 28

MAX EClasses/EPackage 49 24

MIN EClasses/EPackage 5 3

AVG EClasses/EPackage 27 10

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Lessons Learned

DTDs are not appropriate for designing modeling languages

Technical problems Graphical editors (e.g., Omondo) have difficulties in

displaying large models Manual effort for reorganizing the graphical models (layout)

Eclipse plugins require a lot of memory Advantages of automatically generating a draft metamodel

Correct translation of concepts and their interrelationships Visualization of the language fosters understanding With minimal manual refactorings (IDREF) one is able to obtain

metamodel that is equivalent to the original DTD Models that are equivalent to the original XML documents

can be generated. Metamodel still can be improved and semantically

enriched by introducing generalization hierarchies, etc.

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Outlook

Open Issues Extend the WebML Metamodel with WebML concepts

that have not been part of the DTD (Web Services, Process Modeling)

OCL constraints for Links Extend, improve, and evaluate DTD2MOF-Framework

Future Work Applying Aspect-Orientation to

the Model-Driven Development of Ubiquitous Web Applications1

Integration of Web modeling languages – towards a common understanding in the web modeling field.

1A. Schauerhuber, aspectUWA: Applying Aspect-Orientation to the Model-Driven Development of Ubiquitous Web Applications, Student Extravaganza: Spring School, AOSD'06, Bonn, Germany, March 19, 2006.

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References

N. Moreno, P. Fraternalli, and A. Vallecillo. A UML 2.0 Profile for WebML Modeling. Workshop on Model-Driven Web Engineering (MDWE 2006), in conjunction with ICWE'06, Standford Linear Accelerator Center, Palo Alto, California, July 2006.

L. Baresi, S. Colazzo, L. Mainetti, and S. Morasca. W2000: A Modeling Notation for Complex Web Applications. In E. Mendes and N. Mosley (eds.) Web Engineering: Theory and Practice of Metrics and Measurement for Web Development. Springer, 2006.

L. Baresi, F. Garzotto, and M. Maritati. W2000 as a MOF Metamodel. In Proc. of the 6th World Multiconference on Systemics, Cybernetics and Informatics - Web Engineering track. Orlando, USA, July 2002.

N. Koch, A. Kraus. Towards a Common Metamodel for the Development of Web Applications. In Proc. of the 3rd International Conference on Web Engineering (ICWE 2003), July 2003.

P.-A. Muller, P. Studer, F. Fondement, J. Bézivin. Platform independent Web application modeling and development with Netsilon. Software & System Modeling, 4(4), November 2005.

M. Wimmer, A. Schauerhuber, E. Kapsammer, and G. Kramler. From Document Type Definitions to Metamodels: The WebML Case Study. Technical Report. Vienna University of Technology, March 2006.

H. Ma, W. Shao, L. Zhang, Z. Ma, and Y. Jiang. Applying OO Metrics to Assess UML Meta-models. In Proc. of the 7th International Conference on the Unified Modelling Language: Modelling Languages and Applications. Springer-Verlag LNCS 3273, 2004.

Documents

Bridging existing Web Modeling Languages to Model-Driven Engineering: A Metamodel for WebML Andrea Schauerhuber, Manuel Wimmer, Elisabeth Kapsammer Workshop