sheet 1 doceng’03, grenoble, november 2003 model driven architecture based xml processing ivan...

Sheet 1DocEng’03 , Grenoble, November 2003

Model Driven Architecture based

XML Processing

Ivan Kurtev, Klaas van den BergUniversity of Twente, the Netherlands


Outline

Technologies for XML Processing; Problem Statement; Model Driven Architecture (MDA)

Concepts; MDA based XML Processing; Example; Transformation Language; Conclusions;


Context

Applications written in an OO language

Main goal: transform a document into a set of application objects;

Domain

Domain

XMLDocument

ApplicationObjects

ApplicationClasses

Transformation

Encodes data from

Implements concepts

Instances

The Transformation is a recurring task and requires automation


Technologies for XML Processing

XMLDocument

Schema

DOMParser

ProcessingCode

DOM Tree Application Objects

Generic interfaces to XML documents (e.g. DOM)

ApplicationClasses

XMLDocument

Objects

Compilation

Unmarshalling

Instance of Instance of

Data Binding

Tree traversing, class instantiation, type conversions are performed by processing code.

Compilation and Unmarshalling are automated;

Not applicable in case of dissimilarities between the schema and the application structure;


Problem Statement XML Processing:

Definition and execution of transformations between XML documents and application objects;

Requirements: Transformations should be automated; Transformations should produce the desired

application objects;

Current technologies are either low-level or do not always produce the desired application objects;

More powerful transformation techniques are required!

Solution: Application of Model Driven Architecture (MDA) model

transformation techniques;


Basic MDA Concepts

Source Model Transformer Target Model

TransformationSpecification

Model Transformations– The MDA Pattern (from “MDA Guide”):

PlatformIndependentModel (PIM)

PlatformSpecific

Model (PSM)

Separation of system specification from system implementation;

Models:


Meta Modeling and XML (1) In the MDA models can be defined in the Meta Object Facility

(MOF) based on four meta layers; Similar meta layer organization is observed in the XML

technology;

The MOFMMM

The UML MM

A UML Modelm1

A particularuse of m1

Level M3

Level M2

Level M1

Level M0

The Java MM

A UML Modelm2

Another useof m1

Meta Schema(Schema forschemas)

An XMLSchema

An XMLDocument

MOF XMLExample:


Schemas play the role of models for XML documents; Schemas may be considered as MOF models if a proper Schema

meta-model is defined;

MOF

XML SchemaMeta-model

Java Meta-model

an XMLSchema

Java Classes

an XMLDocument

ObjectsM0

M1

M2

M3 instance of

Transformation Specification

Unmarshaling

Transformation Execution

Example:In MOF Data Binding is a model transformation. Arbitrary transformation policiesmay be specified.

Meta Modeling and XML (2)


MDA based XML Processing Document schema is a Source Model (at level M1); Application Classes form a Target Model;

MOF

XML SchemaMeta-model

TransformationMeta-model

Target Meta-model

an XMLSchema

a ConcreteTransformation

a TargetModel

an XMLDocument

Objects

source target

Executed by

M0

M1

M2

M3

TransformationEngine

instance of

Transformations are specified between the source and the target model;

Transformations are executed over source XML documents and result in a set of target objects;


XML Schema Meta-model

Fragment of the XML Schema Meta-model (based on the W3C specification)

+name

TypeDefinition

SimpleTypeDefinition

+abstract+mixed

ComplexTypeDefinition

+derivationType

Derivation

+abstract+topLevel

ElementDeclaration

+topLevel

AttributeDeclaration

1

+derived

1

+base 10..*

0..*

+type

1

0..*

+type

1

+substitutes

0..1

+substitutedBy0..*


Target Meta-modelConstructs: Class, Attribute, Method, Generalization

+name

ModelElement

Feature GeneralizableElement Relationship

Classifier

Class DataType

Attribute Method Generalization

+feature

0..*

+owner

1

+child

1

+generalization0..*

+parent1

+specialization

0..*

Fragment of the target meta-model (subset of UML meta-model)


Example: Address and PersonSource SchemaSimplified version of the “canonical”

PurchaseOrderschema from the XML Schema Primer:

<complexType name="Address"> <sequence> <element name="name“ type="string"/> <element name="street" type="string"/> </sequence></complexType>

<complexType name="USAddress"> <complexContent> <extension base=’Address’> <sequence> <element name="zip " type="string"/> </sequence> </extension> </complexContent></complexType>

Application Classes (implemented in Java):

public class Address{ public String street;}

public class USAddress extends Address{

public String zip;}

public class Person{ private Address address; public String firstName; public String lastName;

public Person(Address address){ ... }}


Example: Target Model The target model wraps the application Java classes Deriving the target model from Java classes:

Java class to a model class; Extension to generalization; Public fields to attributes; Constructor parameters to attributes;

Information not included in the target model: Collections that implement multivalued attributes; Access to the attributes;

+street

Address

+zip

USAddress

+firstName+lastName+address : Address

Person


Example: Transformation SpecificationTransformation Language:

Abstract Syntax: MOF-based Transformation Meta-model ; Concrete Syntax: specified as a grammar; Two types of rules: Class and Attribute Rules;

Class Rules: specify instantiations of classes in the target model based on selection of source components:

personRule ClassRule source [ Address:CT/name:E ]

target [ Person constructor {address} { firstName = getFirstName(source), lastName = getLastName(source) } ]

Pattern

Class to be instantiated

Attribute to be setprior to the instantiation

Attribute to be setafter the instantiation

Example:


Example: Transformation Specification

Attribute Rules: specify how the attribute values are obtained from the source.

addressAttribute AttributeRule source [*:E] target [address]

path=’parent::*’ An XPath navigation expression that locatesthe source nodes associated with the value

Attribute to be set

addressAttribute rule specifies how to locate the value of the address attribute:

And the address object is created by another class rule:

addressRule ClassRule source [ Address:CT ] target [ Address {street} ]

Example:


Adaptation to Java

Transformation language does not specify how objects are created and attributes are set;

In Java: Object creation: constructor, factory method; Attribute access: getter and setter methods, public fields; Multivalued attributes: implemented as collections (array,

Vector, etc.); This is provided separately as additional meta

information;


Transformation Execution

There is no predefined execution order over the rules; Implicit dependencies among the rules:

Constructor attributes are calculated before class instantiation;

Other attributes are set after the instantiation; During execution the dependencies are resolved

Dependency graph is formed; Execution order is determined after a topological sort

over the dependency graph; Circularity prevents the execution of the transformation;


Conclusions

Approach for XML Processing: Based on transformations between source schema and

target application model; Declarative language for defining transformations; Based on the MDA/MOF technology; Allows reuse of existing application classes;

A prototype of an interpreter that supports the core transformation language features is implemented;


Future Work

Applying schema matching techniques for rule identification;

Generalizing the language to the arbitrary model-to-model transformations in the context of MOF;

Reuse and composition of transformations following the composition of the source XML schemas;

More efficient rule execution;

sheet 1 doceng’03, grenoble, november 2003 model driven architecture based xml processing ivan...

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