A CASE Tool for Designing XML Views

Yabing Chen, Tok Wang Ling, Mong Li Lee

May, 2002

Contents

1. Introduction2. Preliminaries3. Architecture of the CASE tool4. An illustrating example5. Related work6. Conclusion7. Q & A

Part 1. Introduction

Introduction XML – eXtensible Markup Language XML Views An introduction to the CASE tool –

XVS

XML – eXtensible Markup Language

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.

Introduction

XML Views 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.

Introduction

An introduction to the CASE tool - XVS

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.

Introduction

Part 2. Preliminaries

Preliminaries ORA-SS data model View Definition Language

ORA-SS data model 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.

Preliminaries

ORA-SS data model (cont.) An object class – a labeled rectangle. A relationship type – (name, n, p, c) An attribute – a labeled circle.

Preliminaries

s u p p lier

s n o p ar t

p n op r ic e

p r o jec t

jn o

p s ,2 ,1 :n ,1 :n

s p ,2 ,1 :n ,1 :n

s p

p r o jec t

jn o :j0 0 1

s u p p lier s u p p lier

s n o :s 0 0 1

p ar t

p r ic e :9 0

p ar t

p n o :p 0 0 2

p r ic e :1 2 0

p ar t

s n o :s 0 0 1

p n o :p 0 0 3

p r ic e :11 0

F i g ur e 1 : O R A-SS Sc he m a D i ag r am

F i g ur e 2 : O R A-SS Ins tanc e D i ag r am

p n o :p 0 0 1

ORA-SS data model (cont.) 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.

Preliminaries

View Definition Language 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.

Preliminaries

Part 3. Architecture of the CASE tool

Architecture of the CASE tool

O R D B M S

X V S

W e b

A pplic a tio n

U s e r Q u e r y( X Q u ery )

A n s we r to Q u e ry( XM L )

D e s i g n G r a p h i c a lV i e w S c h e m a

X M L D o cu m e n t

Tr a n s fo r m /En r i c h(O R A - S S )

Q u e r y R e w r i t e(S Q L )

Ge n e r ate X M LR esu lt

G e n e r a te V i e wD e f i n i t i o n ( X V L )

M ate r ial i z e V ie w

Figure 3. The Architecture of the CASE tool

Modules of our system 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.

Architecture of the CASE tool

Modules of our system (cont.) 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.

Architecture of the CASE tool

Part 4. An illustrating example

An illustrating example

1. Mapping XML document to ORA-SS schema diagram

2. Defining views3. Rewriting XQuery

1. Mapping XML document to ORA-SS schema diagram

Transform an XML document to ORA-SS

An illustrating example

s u p p lie r

s n o p ar t

p n op r ic e

p r o jec t

jn o

<db> <project jno=”j001”> <supplier sno=“s001”> <part pno=“p001”> <price> 100</price> </part> </supplier> <supplier sno=“s002”> <part pno=“p001”> <price> 100</price> </part> </supplier> </project></db>

Figure 4. An XML document on project, supplier and part

Figure 5. The ORA-SS schema diagram of the XML

document

1. Mapping XML document to ORA-SS schema diagram

Enrich the ORA-SS schema with semantics.

An illustrating example

s u p p lie r

s n o p ar t

p n op r ic e

p r o jec t

jn o

Figure 5. The ORA-SS schema diagram of the XML

document

s u p p lie r

s n o p ar t

p n op r ic e

p r o jec t

jn o

js ,2 ,1 :n ,1 :n

s p ,2 ,1 :n ,1 :ns p j,3 ,1 :n ,1 :n

s p

Figure 6. The ORA-SS schema diagram enriched with

semantics

2. Defining views Designing a view by selecting, dropping or restructuring

on the ORA-SS schema.

An illustrating example

p ar t

p n o s u p p lie r

s n o

p r ic e

p r o jec t

jn op ar t

p n o s u p p lie r

s n o

p s

p r ic e

p r o jec t

jn o

F i g ur e 8 : i nval i d vi e w w hi c hs w aps s uppl i e r and par t

F i g ur e 9 : val i d vi e w w hi c hs w aps s uppl i e r and par t

p s ,2 ,1 :n ,1 :np s ,2 ,1 :n ,1 :n

s u p p lie r

s n o p ar t

p n op r ic e

p r o jec t

jn o

js ,2 ,1 :n ,1 :n

s p ,2 ,1 :n ,1 :ns p j,3 ,1 :n ,1 :n

s p

Fig u re 7 . Th e O R A -S S s ch e m ae n rich e d with s e m a n t ics

2. Defining views (cont.) Mapping the view schema to a view definition in XQuery

expression.

An illustrating example

Create View As swap-supplier-partFor $j In document("spj.xml")//projectReturn <project jno={$j/@jno}> { for $pn In distinct($j//part/@pno) Return <part pno={$pn}> { For $s In $j/supplier[part/@pno=$pn] Return <supplier sno={$s/@sno}> { For $p In $s/part[@pno=$pn] Return <price> {$p/price/text()} </price> } </supplier> } </part> } </project>

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

3. Rewriting XQuery Users may issue an XQuery on the views. The following query retrieves all suppliers that

supply part “p001” in project “j001”

An illustrating example

For $s In

view(“swap-supplier-part”)//project[@jno=”j001”]/part[@pno=”p001”]/supplier

Return

<supplier sno={$s/@sno}>

{$s/price}

</supplier>

Select supplier.sno supplier_part.price

From supplier, supplier_part , spj

Where spj.jno=’j001’ and spj.pno=’p001’

and supplier.sno=spj.sno and supplier_part.sno=supplier.sno

and supplier_part.pno=’p001’Figure 11. An XQuery on the

viewFigure 12. The rewritten SQL

query

3. Rewriting XQuery (cont.) We will first get the resulting table shown in figure 12. After tagging, we will get the XML document shown in figure 13.

An illustrating example

<result> <supplier sno="s001"> <price>100</price> </supplier> <supplier sno="s002"> <price>100</price> </supplier></result>

Sno price

S001 100

S002 100

Figure 12. The result in table form

Figure 13. The result in XML form

tagging

Part 5. Related Work

ActiveViews system & MIX system

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,.

Related Work

Comparison

Related Work

  ActiveViews system [AAC+99]

MIX system [BGL+99]XVS

(our system)

Data model XML XML DTD ORA-SS

Storage O2 system N/A ORDBMS

View definition language

OQL-style language XMAS language XQuery language

Query language

Lorel language XMAS language XQuery language

Validation of views

No No Yes

Support projection,

join and restructuring

of views

No No Yes

Support graphical

views designNo No Yes

Part 6. Conclusion

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

Q & A