Schemaless Change detection in XML Documents using Semantic Identifiers

Change Detection in XML Documents

using Semantic Identifiers

BY

KAILAASH BALACHANDRAN

1

Outline

Motivation

Introduction

The Approach

• Identifiers

• 2-step Algorithm

• Axioms

Semantic Change Detection

• Finding Identifiers

• Matching Nodes

Examples

Conclusion

2

Motivation(1)

Fig.2. Version 2

<author>

<name>Dan Brown</name>

<book>

<title>The Da Vinci Code</title>

<publisher>Doubleday</publisher><salesprice>$35</salesprice>

<isbn>0385504209</isbn>

</book>

<book>

<title>Angels & Demons</title>

<publisher>Pocket Star</publisher><price>$56</price>

</book></author>

Fig.1. Version 1

<author>


<book>


<publisher>Doubleday</publisher><price> $35 </price>

</book>

<book>

<title>Angels and Demons</title>

<publisher>Pocket Star</publisher>

<price> $56</price></book>

</author>

3

Motivation(1)

Fig.2. Version 2

<author>


<book>


<publisher>Doubleday</publisher><salesprice>$35</salesprice>

<isbn>0385504209</isbn>

</book>

<book>

<title>Angels & Demons</title>

<publisher>Pocket Star</publisher><price>$56</price>

</book></author>

Fig.1. Version 1

<author>


<book>



</book>

<book>



<price> $56</price></book>

</author>

4

Motivation(2)Fig.3. Version 3

<publisher>Doubleday

<book>


<author>

<name>Dan Brown</name></author>

<price> $35</price>

</book>

</publisher>

<publisher>Pocket Star

<book>


<author><name>Dan Brown</name>

</author>

<price> $56</price>

</book> </publisher>

Fig.1. Version 1

<author>


<book>


<publisher>Doubleday</publisher>

<price> $35 </price>

</book>

<book>

<title>Angels and Demons</title><publisher>Pocket Star</publisher>

<price> $56</price>

</book>

</author>

5

Motivation(2)Fig.3. Version 3


<book>


<author>

<name>Dan Brown</name></author>

<price> $35</price>

</book>

</publisher>


<book>


<author><name>Dan Brown</name>

</author>

<price> $56</price>


Fig.1. Version 1

<author>


<book>



</book>

<book>



<price> $56</price>

</book>

</author>

6

Motivation(3)

Disadvantages of Structural detection approach:

Difficult to associate elements in different versions.

Break down when the changes are significant.

Affects Incremental Evaluation.

High cost of change of data.

7

Introduction

What is Semantic Based Change Detection?

A process of Identifying changes between successive versions of a document

based on its semantics, rather than on the structure of the document.

The Approach:

1. Find Semantic Identifier for each node in the XML model.

2. Compute these Identifiers to associate nodes across multiple versions.

8

Identifiers

Type is list of labels from root to element separated by a ‘/’.

Identifier serves to distinguish elements of same type.

Two nodes x and y, are semantically the same if and only if their identifiers evaluate to

the same result.

Node

x

Node

y

Same Result

Eval(x,L) = Eval(y,L)

where,• x,y are the nodes,

• List of Expressions L = { E1,E2…En}

9

Identifiers

Local Identifier: An identifier is local if it evaluates to descendants of the context

node, otherwise it is non-local.

Version 1:

<author>

<name>Dan Brown</name><book>




</book>

<book>


<publisher>Pocket Star</publisher><price> $56</price>

</book>

</author>

Version 3:


<book><title>The Da Vinci Code</title>

<author>


</author><price> $35</price>

</book>

</publisher>

<publisher>Pocket Star <book>

<title>Angels and Demons</title><author>




10

Identifiers

Local Identifier: An identifier is local if it evaluates to descendants of the context

node, otherwise it is non-local.

Version 1:

<author>

<name>Dan Brown</name><book>




</book>

<book>


<publisher>Pocket Star</publisher><price> $56</price>

</book>

</author>

Version 3:


<book><title>The Da Vinci Code</title>

<author>



</book>

</publisher>

<publisher>Pocket Star <book>





<name> is

local<name> is

non-local

11

Identify nodes based on its

Semantics

The Algorithm

Phase 1:

Bottom up fashion.

Identifies all local identifiers.

Semantically different nodes are identified.

Phase 2:

Runs recursively and identifies non-local identifiers.

All semantically distinct nodes are found.

Any remaining node is a redundant copy of another node in the document.

12


Semantics(Phase 1)


<book>


<author>


</author></book>

</publisher>


<book>



</author></book> </publisher>

Semantically different.

Axiom 1: Nodes that are structurally different are semantically different.

13


Semantics(Phase 1)


<book>


<author>


</author></book>

</publisher>


<book>



</author></book> </publisher>

Are they semantically the same?

Axiom 1: Nodes that are structurally different are semantically different.

14


Semantics(Phase 2)


<book>

<title>The Da Vinci Code</title><author>


</author>

</book>

</publisher>


<book>



</author>


No, because they’re in context of two

different books

Axiom 2: Nodes that are structurally

identical are semantically identical

if and only if their respective parents are semantically identical or if they

are both root nodes.

15


How to handle structural changes ?

Assumption: Identifying information will remain nearby.

X

Y Z YX

A

Z

Version 1 Version 2

16


Type Territory : The territory of a type T is the set of all text nodes that are descendants of the least common ancestor (lca) of all of the type T nodes.

Within the type territory is the territory controlled by individual nodes of that

type.

Node Territory : The territory of a type T node p is the type territory of T excluding all text nodes that are descendants of other type T nodes.

17

Node and Type Territory

document root

lca (p)

p1

p2

p3

node territory of p2node territory of p1

Node territory

type territory of p

18

Finding IdentifiersVersion 1:

<bib>

<author><name>n1</name>

<book>

<title>t1</title>

<publisher>p1</publisher>

</book>

</author><author><name>n2</name>

<book>

<title>t2</title>


</book>

<book>

<title>t1</title><publisher>p1</publisher>

</book></author>

</bib>

Version 2:

<bib>

<pub> p1

<book>

<title>t1</title><author>

<name>n1</name>

</author>

<book>

<pub> p2

<book>

<title>t2</title>

<author>

<name>n2</name>

</author>

<book>

19

Identifiers

<bib>


<book>

<title>t1</title>


</book>

</author>


<book>


</book>

<book>


</book></author>

</bib>

Node IDENTIFIER

book (../author/name/text(),

title/text())

20

IdentifiersValues of Identifiers for <book> in Version 1

<bib>


<book>


</book>

</author>


<book>

<title>t2</title>


</book>

<book>

<title>t1</title>


</book></author>

</bib>

Value of Identifier = n1, t1



21


<bib>

<pub> p1

<book>


<name>n1</name>

</author>

</book>

</pub>

<pub> p2

<book>

<title>t2</title>

<author>

<name>n2</name>

</author>

</book></pub>

</bib>

22


<bib>

<pub> p1

<book>


<name>n1</name>

</author>

</book>

</pub>

<pub> p2

<book>

<title>t2</title>

<author>

<name>n2</name>

</author>

</book></pub>

</bib>

Value of Identifier = p1, t1

Value of Identifier = p2, t2

23

Identifiers

Node IDENTIFIER

book (top) n1 , t1

book

(middle)n2 , t2

book

(bottom)

n2 , t1

Values of Identifiers for <book> in both versions:

Node IDENTIFIER

book 1 (top) p1 , t1

book 2

(bottom)p2 , t2

Version 1 Version 2

How to map both ?

24

Matching

Admits: q admits p if and only if q is in the node territory of p.

Nodes p and q are matched if and only if p and q admit each other.

Consider nodes p and q that reside in different versions Vp and Vq.

q1, q2….qn

q1, q2….qn

Node q in Vq Node p in Vp

25


n1

author author

namebook

name bookbook

bib

title pub n2

t1 p1 t2 p2 t1

pubtitle title pub

p1

bib

pub pub

p1 book p2 book

titleauthor author

title author

t1name name

t2 name

n1 n2 n2

Version 1

Version 2

Book matches:

26


n1

author author

name bookname

book book

bib

title pub n2

t1 p1 t2 p2 t1

pubtitle title pub

p1

bib

pub pub

p1 book p2 book

titleauthor author

title author

t1name name

t2name

n1 n2 n2

Version 1

Version 2

Book matches:

admits

27


n1

author author

name bookname

book book

bib

title pub n2

t1 p1 t2 p2 t1

pubtitle title pub

p1

bib

pub pub

p1 book p2 book

titleauthorauthor

title author

t1name name

t2name

n1 n2 n2

Version 1

Version 2

Book matches:

Node match

28


n1

author author

name bookname

book book

bib

title pub n2

t1 p1 t2 p2 t1

pubtitle title pub

p1

bib

pub pub

p1 book p2 book

titleauthorauthor

title author

t1name name

t2name

n1 n2 n2

Version 1

Version 2

Book matches:

Node match

29


n1

author author

name bookname

book book

bib

title pub n2

t1 p1 t2 p2 t1

pubtitle title pub

p1

bib

pub pub

p1 book p2 book

titleauthor author

title author

t1name name

t2name

n1 n2 n2

Version 1

Version 2

Author matches:

30

Conclusion

Semantic change detection technique.

• Find identifiers for each node in the XML document

• Associate nodes across versions.

Information that identifies an element is conserved across changes.

Time complexity is O(n*log(n))

We can match nodes even when structural changes are significant.

31

Schemaless Change detection in XML Documents using Semantic Identifiers

Technology

different nodes

angels demonspocket

vinci codedoubleday

type t nodes

root nodes

yx version

nodes x

text nodes