A CASE Tool for Designing XML Views

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A CASE Tool for Designing XML Views

• Yabing Chen, Tok Wang Ling, Mong Li Lee
• May, 2002

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Contents

• Introduction
• Preliminaries
• Architecture of the CASE tool
• An illustrating example
• Related work
• Conclusion
• Q A

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Part 1. Introduction
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Introduction

• XML eXtensible Markup Language
• XML Views
• An introduction to the CASE tool XVS

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XML eXtensible Markup Language
Introduction

• XML originally a document markup language.
• XML now standard for publishing and exchanging
  data on the web.
• XML enforces explicit structuring.
• XML suitable for express more structured data.

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XML Views
Introduction

• XML views are analogous to Relational views.
• They provide logical data independence that masks
  changes in the conceptual schemas.
• They also increase the flexibility of a database
  that allows multiple users to see the data in
  different ways.
• XML Views are implemented as an mediator on top
  of the database.
• Rlational database, such as Oracle 9i, SQL Sever.
• Native XML database, such Software AG Tamino.

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An introduction to the CASE tool - XVS
Introduction

• XVS XML Views System.
• a novel case tool for designing XML views.
• Provides for a graphical views design facility.
• Validates all designed views.
• Stores XML data in an object-relational database.

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Part 2. Preliminaries
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Preliminaries

• ORA-SS data model
• View Definition Language

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ORA-SS data model
Preliminaries

• ORA-SS Object-Relationship-Attribute Semi
  Structured data model.
• Three basic concepts object classes,
  relationship types and attributes.
• Object class an entity type in ER diagram or an
  element in XML.
• Relationship type indicate existing semantic
  relationships among object classes.
• Attributes properties, may belong to object
  classes or relationship types.

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ORA-SS data model (cont.)
Preliminaries

• An object class a labeled rectangle.
• A relationship type (name, n, p, c)
• An attribute a labeled circle.

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ORA-SS data model (cont.)
Preliminaries

• ORA-SS A semantically rich data model.
• Reflects nested structure of semistructured data.
• Distinguishes between object classes,
  relationship types and attributes.
• Distinguishes between attributes of relationship
  types and attributes of object classes.
• Such semantics is essential for designing valid
  XML views and efficient storage.
• However, existing data model cannot support such
  semantics.

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View Definition Language
Preliminaries

• W3C standard XQuery.
• We adopt FLWR expression to define views.
• FLWR expression For, Let, Where and Return
  clauses.
• We also adopt XQuery as the query language to
  query views.

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Part 3. Architecture of the CASE tool
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Architecture of the CASE tool
Figure 3. The Architecture of the CASE tool
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Modules of our system
Architecture of the CASE tool

• Transform/Enrich ORA-SS.
• This module takes an XML document and generates
  the corresponding ORA-SS graphical schema
  diagram.
• It also allows users to enrich the ORA-SS schema
  diagram to add necessary semantic information for
  XML views design.
• Design graphical view schema.
• This module allows users to graphically design
  views over source schema.
• Generate view definition.
• This module generates a view definition in FLWR
  expression from the graphical view schema.

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Modules of our system (cont.)
Architecture of the CASE tool

• Query Rewrite
• This module rewrite a XQuery over the view into
  SQL query over the source database.
• Generate XML result
• This module tags the resulting table returned by
  SQL query.
• Then it generates the resulting XML document.
• Materialize view
• This module executes the XQuery expression in the
  view definition and generates the view documents.

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Part 4. An illustrating example
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An illustrating example

• Mapping XML document to ORA-SS schema diagram
• Defining views
• Rewriting XQuery

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1. Mapping XML document to ORA-SS schema diagram
An illustrating example

• Transform an XML document to ORA-SS

ltdbgt ltproject jnoj001gt ltsupplier
snos001gt ltpart pnop001gt
ltpricegt 100lt/pricegt lt/partgt
lt/suppliergt ltsupplier snos002gt
ltpart pnop001gt ltpricegt
100lt/pricegt lt/partgt lt/suppliergt
lt/projectgt lt/dbgt
Figure 4. An XML document on project, supplier
and part
Figure 5. The ORA-SS schema diagram of the XML
document
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1. Mapping XML document to ORA-SS schema diagram
An illustrating example

• Enrich the ORA-SS schema with semantics.

Figure 5. The ORA-SS schema diagram of the XML
document
Figure 6. The ORA-SS schema diagram enriched with
semantics
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2. Defining views
An illustrating example

• Designing a view by selecting, dropping or
  restructuring on the ORA-SS schema.

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2. Defining views (cont.)
An illustrating example

• Mapping the view schema to a view definition in
  XQuery expression.

Create View As swap-supplier-part For j In
document("spj.xml")//project Return
ltproject jnoj/_at_jnogt for pn In
distinct(j//part/_at_pno) Return
ltpart pnopngt For
s In j/supplierpart/_at_pnopn
Return ltsupplier
snos/_at_snogt For p In
s/part_at_pnopn
Return ltpricegt
p/price/text() lt/pricegt
lt/suppliergt
lt/partgt
lt/projectgt

• The mapping process may be divided into two
  steps
• Mapping the view schema to an intermediary view
  definition, which is generated according to the
  operation on the view schema.
• Mapping the intermediary definition to the view
  definition in XQuery expression.

Figure 10. The View definition in XQuery
expression
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3. Rewriting XQuery
An illustrating example

• Users may issue an XQuery on the views.
• The following query retrieves all suppliers that
  supply part p001 in project j001

For s In view(swap-supplier-part)//projec
t_at_jnoj001/part_at_pnop001/supplier Return
ltsupplier snos/_at_snogt
s/price lt/suppliergt
Select supplier.sno supplier_part.price From
supplier, supplier_part , spj Where
spj.jnoj001 and spj.pnop001 and
supplier.snospj.sno and supplier_part.snosupplie
r.sno and supplier_part.pnop001
Figure 11. An XQuery on the view
Figure 12. The rewritten SQL query
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3. Rewriting XQuery (cont.)
An illustrating example

• We will first get the resulting table shown in
  figure 12.
• After tagging, we will get the XML document shown
  in figure 13.

ltresultgt ltsupplier sno"s001"gt
ltpricegt100lt/pricegt lt/suppliergt
ltsupplier sno"s002"gt
ltpricegt100lt/pricegt lt/suppliergt lt/resultgt
tagging
Figure 12. The result in table form
Figure 13. The result in XML form
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Part 5. Related Work
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ActiveViews system MIX system
Related Work

• ActiveViews system.
• Adopt XML as the data model to define view.
• Every view is presented as an object.
• A view includes not only data, but also method.
• MIX system.
• It provides a virtual view of underlying
  heterogeneous sources.
• It adopts XML DTD as the data model.
• Most other works export relational data as XML
  views, such as XPERANTO, etc,.

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Comparison

Related Work
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Part 6. Conclusion
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Conclusion

• A CASE tool for XML views XVS
• Preliminaries
• ORA-SS as the data model.
• XQuery as the view language.
• Novel features
• More flexible XML views. More operation such as
  projection, join and restructuring.
• Validating XML views.
• Future work
• Query optimization
• View update

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Q A