Maintaining Semantics in
the Design of Valid and
Reversible SemiStructured
Views
Yabing Chen, Tok Wang Ling, Mong Li Lee
Department of Computer Science
National University of Singapore
1
Outline
Introduction
 Motivating Example
 Design Rules for Swap Operators
 Conclusion

2
Introduction

XML
 The
dominant standard for exchanging data
on the Internet

XML Views
 Exploit
the potential of XML
 Secure the source data
 Provide an application-specific view
3
Related Work

XML Views on Relational Database

SilkRoute [1] [2]


XPERANTO [3] [4]


uses a canonical mapping to create a default XML view from relational data
ROLEX [14]


Two different language to define and query the views over relational data
Uses XSLT to define XML views.
XML Views on XML Data

Xyleme [15]


Define XML views using DTD
ActiveView [16]

Define views with active features
[1]M. Fernandez, W. Tan, D. Suciu, “Efficient Evaluation of XML Middleware Queries”, ACM SIGMOD, pp. 103-114, 2001.
[2] M. Fernandez, W. Tan, D. Suciu, “SilkRoute: Trading Between Relations and XML”, World Wide Web Conference, 1999.
[3] M. Carey, J. Kiernan, J. hanmugasundaram, et. al., “XPERANTO: A Middleware for Publishing Object-Relational Data as XML Documents”,
VLDB, pp. 646-648, 2000.
[4] M. Carey, D. Florescu, Z. Ives, et. al., “XPERANTO: Publishing Object-Relational Data as XML”, WebDB Workshop, 2000.
[15] Sophie Cluet, Pieanglo Veltri, Dan Vodislav, Views in a large scale xml repository, VLDB 2001, pp. 271-280.
[16] Serge Abiteboul, Sophie Cluet, Laurent Mignet, et. Al. Active views for electronic commerce, VLDB 1999, pp.138-149.
4
Weakness of related work

Disadvantage of the main related work
 Ignore

semantic information in source data
For example, ignore the difference between object
class, attribute and relationship in schema
 Cannot
check the validity of designed views
 Difficult to use query languages to define
views

Proprietary language or XQuery
5
Our approach

Our approach for XML views

Our previous work

Design valid XML Views [9]



Based on a semantically rich model - ORA-SS [18]
Use query operators, such as selection, drop, swap, join, etc.
Our current work (this paper)


A complete set of rules for swap operators & reversible
views
Maintain participation constraints for relationship types in
the views.
[9] Ya Bing. Chen, Tok Wang Ling, Mong Li Lee, “Designing Valid XML Views”, ER Conference, 2002
[18] Gillian Dobbie, Xiao Ying Wu, Tok Wang Ling, Mong Li Lee, ORA-SS: An Object-Relationship-Attribute Model for
SemiStructured Data, Technical Report TR21/00, School of Computing, National University of Singapore, 2000.
6
Motivating Example

ORA-SS data model
Object class – Rectangle
 Attribute – circle
 Relationship type – label on the
connection between object classes


Difference between ORA-SS and
ER diagram



ORA-SS is hierarchical structure
ER is flat structure
Difference between ORA-SS and
other XML models

More semantics expressed. i.e.
differentiate object class and
attribute, differentiate the
relationship attributes and object
class attributes
course
cs,2,1:n,1:n
code title
cl,2,1:n,1:n
student
lecturer
cl
cs
cst,3,1:n,1:n
stfNo
*
stuNo name hobby grade
tutor
name office work load
cst
stfNo office feedback
7
Motivating Example (cont.)

Invalid view may be created by swapping course & student incorrectly

Relationship attribute grade relocated wrongly.
 Relationship type cl disappears.
course
student
cs,2,1:n,1:n
cl,2,1:n,1:n
cs
cs,2,1:n,1:n
*
code title
student
lecturer
cl
cs
stuNo name hobby grade
course
lecturer
cst,3,1:n,1:n
cst,3,1:n,1:n
stfNo
*
stuNo name hobby grade
Swap course
& student
tutor
name office work load
code title
cst
stfNo name office work load
tutor
cst
stfNo office feedback
Source Schema
stfNo office feedback
Invalid view Schema
8
Motivating Example (cont.)

Fortunately, valid view can be created based on our developed rules.

Relationship attribute grade relocated correctly.
 Relationship type cl is kept in the view correctly.
course
student
cs,2,1:n,1:n
cs,2,1:n,1:n
cl,2,1:n,1:n
*
stuNo name hobby
code title
student
lecturer
cl
cs
cst,3,1:n,1:n
stfNo
*
stuNo name hobby grade
tutor
name office work load
cst
stfNo office feedback
Source Schema
Swap course
& student
course
cs
code title grade
cl, 2, 1:n, 1:n
cst,3,1:n,1:n
lecturer
tutor
cst
cl
stfNo office feedback stfNo name office work load
Valid view Schema
9
Swap Operators

Our previous work
 Select,
join and drop operator.
 Simple rules for swap operator

Our current work
 Detailed
and complete rules for swap operator
 Reversible views

A view is reversible if its source schema can be produced
back by applying swap operator on the view
10
Swap Operator (cont.)

Rule Swap_1: move attributes of Oi and Oj
with Oi and Oj
Oi
ki
Oj
ai
Swap Oi & Oj
kj
Oa
Oa
Reversible by applying
the same rule
Oj
kj
aj
aj
Oi
ki
ai
11
Swap Operator (cont.)

Relationship types affected:
Oi
Oa
Oa
Oa
Oc
Oc
Oc
The Second
Category
Oj
Oj
Ok
Ob
Ob
Ob
The First
Category
Oi
Oi
Od
The path from Oj up to Oi
and its ascendants
Ok
Oj
Od
The path involving Oi and
its branch object class
The Third
Category
Ok
Od
The path involving Oj and
its descendants
12
Swap Operator (cont.)

Rule Swap_2: handles the first category of relationship types

Attach attributes of R at the lowest object class
 Reason: keep the relationship attributes meaningful in the view

Property of first category of relationship types:

The path from Oj up to Oi and its ascendants
Oi
Oj
Swap Oi & Oj
Oa
R(Oi, Oa Oj)
,
Oj
R
attribute
Oa
Reversible by applying
the same rule
R(Oi,Oa Oj)
,
Oi
R
attribute
13
Swap Operator (cont.)

Rule Swap_3: handles the second category of relationship types

Attach sub trees of Oi or Oa to Oi
 Reason: keep the relationship meaningful in the view

Property of the second category of relationship types:

The path involving Oi and its branch object classes
Oj
Oi
R1(Oi, Ob)
Ob
Swap Oi & Oj
Oa
Oa
R2(Oi, Oa, Oc)
Oj
Oc
Reversible by applying
the Rule Swap_4
R2(Oi, Oa, Oc)
Oc
Oi
R1(Oi, Ob)
Ob
14
Swap Operator (cont.)

Rule Swap_4: handle the third category of relationship types

Move sub trees of Oj accordingly
 Reason: keep the relationship meaningful in the view

Property of the third category of relationship types:

The path involving Oj and its descendants
Oj
Oi
Swap Oi & Oj
Oa
Oa
R1(Oa, Oj, Ok)
Ok
Oj
R1(Oa, Oj, Ok)
Reversible by applying
the Rule Swap_3 & 4
R2(Oa, Oj, Od)
Od
Oi
R2(Oa, Oj, Od)
Od
R3(Oi, Oj, Od, Oe)
Ok
Oe
R3(Oi, Oj, Od, Oe)
Oe
15
Conclusion

An approach to maintaining semantics in
designing views
 A complete
set of rules for the swap operator
 Keep the relationship types correct in the views
 Maintain the view reversibility


The first work to maintain semantics (i.e.
relationship types)
Provide for a more robust view mechanism to
guarantee the valid views design
16
Thanks!
17
References
1. Serge. Abiteboul, S. Cluet, L. Mignet, et. al., “Active views for electronic commerce”, VLDB, pp.138-149, 1999.
2. Chaitanya. Baru, A. Gupta, B. Ludaescher, et. al., “XML-Based Information Mediation with MIX”, ACM SIGMOD
Demo, 1999.
3. Michael. Carey, J. Kiernan, J. hanmugasundaram, et. al., “XPERANTO: A Middleware for Publishing ObjectRelational Data as XML Documents”, VLDB, pp. 646-648, 2000.
4. Michael. Carey, D. Florescu, Z. Ives, et. al., “XPERANTO: Publishing Object-Relational Data as XML”, WebDB
Workshop, 2000.
5. Ya Bing. Chen, Tok Wang Ling, Mong Li Lee, “Designing Valid XML Views”, ER Conference, 2002
6. Ya Bing Chen, Tok Wang Ling, Mong Li Lee, “Automatic Generation of SQLX Definitions from ORA-SS Views”,
DASFAA, 2004.
7. Sophie. Cluet, P. Veltri, D. Vodislav, “Views in a large scale xml repository”, VLDB, pp. 271-280, 2001.
8. Gillian. Dobbie, X.Y Wu, T.W Ling, M.L Lee, “ORA-SS: An Object-Relationship-Attribute Model for SemiStructured
Data”, Technical Report TR21/00, School of Computing, National University of Singapore, 2000.
9. Mary. Fernandez, W. Tan, D. Suciu, “Efficient Evaluation of XML Middleware Queries”, ACM SIGMOD, pp. 103-114,
2001.
10. Mary. Fernandez, W. Tan, D. Suciu, “SilkRoute: Trading Between Relations and XML”, World Wide Web
Conference, 1999.
11. Philip. Bohannon, H. Korth, P. Narayan, S. Ganguly, and P. Shenoy. Optimizing view queries in ROLEX to support
navigable tree results. VLDB, 2002.
12. Alin. Deutsch and V. Tannen. MARS: A System for Publishing XML from Mixed and Redundant Storage. VLDB,
2003.
18