Conceptual Modeling Issues in Web Applications

enhanced with Web services

Sara Comai, Politecnico di Milanosara.comai@polimi.it

In collaboration with: Marco Brambilla, Stefano Ceri, Piero Fraternali and Ioana Manolescu

WWW Workshop ESSW2003 May 20, 2003 - Budapest

Introduction:table of contents

The scenario of Web application development Motivations of model-driven Web development extended with Web servicesThe WebML approach and its extension with Web services

Conceptual primitives for Web servicesSome examplesImplementation in WebRatio

Conclusions and future directions

Current Web Applications development

The focus of Web applications is shifting from the mere publication of dynamic content to the integrated publication of

content and services

Services can be used to compose integrated workflows, to support business processes

Web services and model-driven approaches

Technological background: SOAP, UDDI, WSDL, BPEL4WS, WSCI, and so onDevelopment methodologies: new methods and CASE tools are requiredAim of this work:

Conceptual modeling and automatic implementation of Web applications interacting with Web servicesPrimitives for a Web modeling language

Web Modeling Language (WebML)

WebML: a conceptual language for high-level design of data-intensive Web applications

Defined in 1998, widely published: Ceri, Fraternali at al. Designing data-intensive Web applications, Morgan Kauffman, Dec. 2002

Adopted in many universities worldwide

Commercially implemented (www.webratio.com)

Used for developing several applications:www.acer-euro.com, www.aceradvantage.com, www.elet.polimi.it, www.image.co.uk,...

WebML basic concepts

Web application = Structure + Hypertext + Presentation

data model

entities,relationships

navigation + composition model

units, pages, links, site views

presentation

styles

WebML hypertexts

Papers Page

Papers Index

Paper Paper[OID=CurrPaper]

Paper DataCurrPaper:OID

Authors Page

Authors Multidata

Author

All AuthorsIndex of Papers

•Daml-s and WSDL•WebML•Web services

Selected paper

title: Web services abstract: XXX

Go to all authors page

WebML and operations

Entry - Author Page

Entry unit Modify

Author

Error Page

KO

OK Success Page

Insert Your Data

•Fname•Lname

submit

Web services operations

Solicit-responseservice operation

Op. name

Request-responseservice operation

Op. name

Notificationservice operation

Op. name

One-wayservice operation

Op. name

Web service operations corresponding to the WSDL operation types

Further building blocks are needed for integrating Web services in Web applications

Management of input/output messages

Typical use of Web services in Web applications: Perform specific tasks and possibly used the data returned by the invoked Web service to define the content of Web pagesNo need of implementing them directly or of storing the data required for computing them

The integration requires: Managing input/output messages (XML format)Marshalling of the application data into XML and vice versaIn our approach: preserve E-R data model and http-like parameter passing

Example of Web service invocation

Send Mail

Compose ComposeMessage

Send Mail Mail sent

Error page

to, subject,body bodyMsg

KO KO

Chains of Web services

Adapter unit for: Composing the input message of a Web serviceDecomposing the output message of a Web serviceCalling multiple Web services in sequence, adapting their input and output

Enter City

Input City ComposeMessage

CityToZipcity bodyMsg

TransformMsgouputMsg bodyMsg

ZipToTemp DecomposeMessage

outputMsg

Temperature page

Confirm datatemp

Storing the data retrieved from Web services

In many applications data retrieved from Web services need also to be stored in local data repository

Persistent storage: database updatesTemporary storage: e.g., until the user disconnects from the application in main memory

Enter City

Input City ComposeMessage

CityToZip

City page

city bodyMsgDecompose

MessageouputMsg zipCode

Create CIty

City<name := cityName>

<zip := zipCode>

City Multidata

City

city

V V

Lifetime of main memory entities

Lifetime of main memory entities: user sessionIn many cases shorter time is needed, e.g., only between two calls of the same Web serviceDifferent policies to fine tune the behavior of update operations on main memory objects:

FLUSH: each time an entity is updated the new data replace any pre-existing dataPRESERVE: each time an entity is updated the new data is added to any pre-existing data

Managing Web services data

Web services are not developed by the creator of the Web application, therefore:

To build a single entity instance several Web services calls may be neededThe data for composing an input message may be spread across different application entitiesThe data obtained from an output message may be stored into application entities with a different structure

Creation of new instances

Different services may retrieve different pieces of information of the same object or sub-schemaThe same Web service may be used at different times to retrieve different pieces of information for the same object

Policies for managing the cumulative update of data

If the instance is “new” insert the new instanceIf the instance already exists:

No action: keep existing instance

Overwrite: keep only the new instance data

Extend: overwrite with the new instance data

Materialization and dematerialization

Need of creating instances of complex data sub-schemata, involving several related entities, fro the output of a service call

Materialization operation

Need of assembling the input message of a service from instances of complex data sub-schemata

Dematerialization operation

Materialization and dematerialization /2

Intermediate XML format: canonical XML schema

<?xml version="1.0" encoding="UTF-8"?>

<root>

<entity id="Ent1">

<instance>

<attribute id="oid">item1</attribute>

<attribute id="att1"> ... </attribute>

</instance> …

</entity>

<entity id="Ent2">

<instance>

<attribute id="oid">object1</attribute>

<attribute id="att2"> ... </attribute>

</instance>

<instance>

<attribute id="oid">object2</attribute>

<attribute id="att2"> ... </attribute>

</instance>

</entity>

<relationship id="rel_Ent1_Ent2">

<instance>

<source-oid>item1</source-oid>

<target-oid>object2</target-oid>

</instance>

<instance>

<source-oid>item1</source-oid>

<target-oid>object2</target-oid>

</instance>

</relationship>

</root>

MaterializerDematerializerXML-ER XML-ER

Example: Google searchWeb Search

Search the Web ComposeMessage

GoogleSearchkeywords bodyMsg

Transform intoXML-ER

ouputMsg XML-ER

Materialize

V

All Results (max10)

GoogleResultElements

Categories

GoogleDirectoryCategory

V

V

...

Example: Google searchWeb Search

Search the Web ComposeMessage

GoogleSearchkeywords bodyMsg

Transform intoXML-ER

ouputMsg XML-ER

Materialize

V

All Results (max10)

GoogleResultElements

Categories

GoogleDirectoryCategory

V

V

...

Implementation

Web Ratio case tool: integrate environment for the visual specification of Web applications and the automatic generation of code for the J2EE and Microsoft .NET platformReal examples using these concepts:

http://www.webratio.com/webservicedemo

Conclusions and future work

Conclusions: Requirements and primitives to model Web applications interacting with Web services with the aim of providing and automatic implementation of such integration Building blocks:

Supporting the transformation of application data into Web services data and vice versaProviding different storage alternativesProviding specific operations for representing at the conceptual level common processes deriving from the integration of Web services

Future work: Adding semantics to the adapter unit Integrating service-centric applications with workflows

Implementation

WebRatio case tool

Style sheet library

Built-in taglibraries

HTML

Third partyauthoring

tools

XML XSL

Data Mapping

Data Design Site Design Presentation

WebRatio Design Layer

Code Generator

Application Server

WebRatio Runtime Layer

DataSources

Unit library

Customcomponents

Custom unitlibrary

Architecture of WebRatio

Model

SOAP Client(remote peer)HTTP Client

(Browser)

HTTP server + SOAP listener

data tier

Business tierpage services

unit services

operation services

ControllerViewpage templates

Actions

Pageactions

Operationactions

State objects

Webservice

Formbeans

Unitbeans

Example of XSL transformation

<?xml version="1.0"?>

<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"

version="1.0">

 

<xsl:param name="to"/>

<xsl:param name="subject"/>

<xsl:param name="body"/>

<xsl:template match="/">

<!-- other elements composing the message body -->

<to xsi:type="xsd:string"><xsl:value-of select="$to"/></to>

<subject xsi:type="xsd:string"><xsl:value-of

select="$subject"/></subject>

<body xsi:type="xsd:string"><xsl:value-of select="$body"/></body>

<!-- other elements composing the message body-->

</xsl:template>

 

</xsl:stylesheet>