Conceptual Modeling Issues in Web Applications enhanced with Web services

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Conceptual Modeling Issues in Web Applications
enhanced with Web services

• Sara Comai, Politecnico di Milano
• sara.comai_at_polimi.it
• In collaboration with Marco Brambilla, Stefano
  Ceri, Piero Fraternali and Ioana Manolescu
• WWW Workshop ESSW2003
• May 20, 2003 - Budapest

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Introductiontable of contents

• The scenario of Web application development
• Motivations of model-driven Web development
  extended with Web services
• The WebML approach and its extension with Web
  services
• Conceptual primitives for Web services
• Some examples
• Implementation in WebRatio
• Conclusions and future directions

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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

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Web services and model-driven approaches

• Technological background SOAP, UDDI, WSDL,
  BPEL4WS, WSCI, and so on
• Development methodologies new methods and CASE
  tools are required
• Aim of this work
• Conceptual modeling and automatic implementation
  of Web applications interacting with Web services
• Primitives for a Web modeling language

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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,...

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WebML basic concepts

• Web application
• Structure Hypertext
  Presentation

entities,relationships
data model
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WebML hypertexts
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WebML and operations
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Web services operations

• Web service operations corresponding to the WSDL
  operation types
• Further building blocks are needed for
  integrating Web services in Web applications

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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 pages
• No 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 versa
• In our approach preserve E-R data model and
  http-like parameter passing

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Example of Web service invocation
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Chains of Web services

• Adapter unit for
• Composing the input message of a Web service
• Decomposing the output message of a Web service
• Calling multiple Web services in sequence,
  adapting their input and output

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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 updates
• Temporary storage e.g., until the user
  disconnects from the application ? in main memory

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Lifetime of main memory entities

• Lifetime of main memory entities user session
• In many cases shorter time is needed, e.g., only
  between two calls of the same Web service
• Different 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 data
• PRESERVE each time an entity is updated the new
  data is added to any pre-existing data

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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 needed
• The data for composing an input message may be
  spread across different application entities
• The data obtained from an output message may be
  stored into application entities with a different
  structure

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Creation of new instances

• Different services may retrieve different pieces
  of information of the same object or sub-schema
• The 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 instance
• If the instance already exists
• No action keep existing instance
• Overwrite keep only the new instance data
• Extend overwrite with the new instance data

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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

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Materialization and dematerialization /2

• Intermediate XML format canonical XML schema
• lt?xml version"1.0" encoding"UTF-8"?gt
• ltrootgt
• ltentity id"Ent1"gt
• ltinstancegt
• ltattribute id"oid"gtitem1lt/attributegt
• ltattribute id"att1"gt ... lt/attributegt
• lt/instancegt
• lt/entitygt
• ltentity id"Ent2"gt
• ltinstancegt
• ltattribute id"oid"gtobject1lt/attributegt
• ltattribute id"att2"gt ... lt/attributegt
• lt/instancegt
• ltinstancegt
• ltattribute id"oid"gtobject2lt/attributegt
• ltattribute id"att2"gt ... lt/attributegt
• lt/instancegt

• ltrelationship id"rel_Ent1_Ent2"gt
• ltinstancegt
• ltsource-oidgtitem1lt/source-oidgt
• lttarget-oidgtobject2lt/target-oidgt
• lt/instancegt
• ltinstancegt
• ltsource-oidgtitem1lt/source-oidgt
• lttarget-oidgtobject2lt/target-oidgt
• lt/instancegt
• lt/relationshipgt
• lt/rootgt

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Example Google search
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Example Google search
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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 platform
• Real examples using these concepts
• http//www.webratio.com/webservicedemo

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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 versa
• Providing different storage alternatives
• Providing 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

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Implementation

• WebRatio case tool

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Architecture of WebRatio
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Example of XSL transformation

• lt?xml version"1.0"?gt
• ltxslstylesheet xmlnsxsl"http//www.w3.org/1999/
  XSL/Transform"
• version"1.0"gt
•  
• ltxslparam name"to"/gt
• ltxslparam name"subject"/gt
• ltxslparam name"body"/gt
• ltxsltemplate match"/"gt
• lt!-- other elements composing the message
  body --gt
• ltto xsitype"xsdstring"gtltxslvalue-of
  select"to"/gtlt/togt
• ltsubject xsitype"xsdstring"gtltxslvalue-of
  
• 
  select"subject"/gtlt/subjectgt
• ltbody xsitype"xsdstring"gtltxslvalue-of
  select"body"/gtlt/bodygt
• lt!-- other elements composing the message
  body--gt
• lt/xsltemplategt
•  
• lt/xslstylesheetgt