AN AUTOMATIC GENERATION METHOD OF DIFFERENTIAL

XSLT STYLESHEET FROM TWO XML DOCUMENTS

Takeshi Kato, Hidetoshi Ueno, Norihiro Ishikawa

Network Management Development Department, NTT DoCoMo, Inc., 3-5 Hikarino-oka, Yokosuka, Kanagawa, JAPAN

Keywords: XML, DOM, XSLT, Differential Data

Abstract: We propose a differential XSLT stylesheet generation method for arbitrary pairs of XML contents. It is

possible to obtain the revised XML document by supplying the XSLT stylesheet with the differential data to

the original XML document. Comparing with sending whole revised XML document, the original XML

document can be updated by sending less information, the differential data. This paper introduces a

difference detection algorithm based on the DOM tree and a difference representation method that permits

the expression of difference information. We also discuss a new XSLT function for the proposed method.

We also introduce prototype software implemented based on proposed method and evaluation result that

shows the effectiveness of our method. An experiment shows that the proposed method is suitable for

updating XML contents, especially for web service in the costly mobile network.

1 INTRODUCTION

XML (eXtensible Markup Language)[Bray, 2000] is

an extensible meta-language that is being widely

applied in description languages such as XHTML

(eXtensible HyperText Markup Language), SVG

(Scalable Vector Graphic) and CC/PP (Composite

Capability / Preference Profiles) as well as

communication protocols such as SOAP (Simple

Object Access Protocol). Unfortunately, XML

content is generally large compared to CSV (Comma

Separated Value) and TLV (Tag-Length-Value)

content because XML uses element tags, attributes,

and XML declarations. In mobile web services,

XHTML[Baker, 2000] mobile profile has become

the standard markup language for mobile phones.

Retransmitting the whole content wastes bandwidth

and time, especially in the wireless network. It is

becoming more and more important to promote

efficiency in the update process and version control

of XML data. An effective idea is updating content

locally by using difference data because the

difference between the old content and the updated

content tends to be small. Mogul et al (1997)

confirmed the benefit of transmitting just the

difference data, for example HTTP Delta-

encoding[Mogul, 2002]. If the differential data of

two XML documents is generated and transmitted

instead of the whole document, the amount of

transmitted data can be greatly reduced. When a

client receives the differential data, it regenerates the

new content, by applying the differential content to

the original content.

To realize the above scenario, we propose a

technique for the automatic generation method of a

differential XSLT stylesheet from two arbitrary

XML documents and show the availability of

description of difference data using a differential

XSLT stylesheet. This technique can also be

provided to web services such as push information

delivery service, weblog service and so on, in which

content need to be frequently and partially updated.

The proposed technique can promote efficiency in

the update process and version control of them.

In this paper, section 2 describes overview of the

proposed method. In section 3, the prototype

software and the results of experiments are

mentioned. Section 4 proposes some extensions to

XSLT for the proposed method and related works

are addressed in Section 5. We conclude this paper

in Section 6.

2 PROCESS OF DIFFERENTIAL

XSLT STYLESHEET

GENERATION

The proposed method uses XSLT (eXtensible

Stylesheet Language Transformations) [Clark, 2000]

Kato T., Ueno H. and Ishikawa N. (2005).

AN AUTOMATIC GENERATION METHOD OF DIFFERENTIAL XSLT STYLESHEET FROM TWO XML DOCUMENTS.

In Proceedings of the First International Conference on Web Information Systems and Technologies, pages 5-12

DOI: 10.5220/0001229300050012

 SciTePress

for updating XML document. XSLT is a language

that provides the function of data structure

transformation for XML documents. We adopted the

Document Object Model (DOM) [Le Hors, 2000] to

express the XML data structure. An original and

updated XML documents are parsed and converted

into two DOM trees. We generate differential XSLT

stylesheets in three steps because it is difficult to

perfectly extract differential data in one operation.

The proposed method is shown in Fig. 1.

Step-1 Difference Detection Process

The differences between the two DOM trees are

detected. In this process, common parts and

differential parts are identified.

Step-2 Difference Extraction Process

We define added nodes, deleted nodes and

change nodes as differential data. In this process,

added nodes, deleted nodes and change nodes are

classified as described later.

Step-3 Difference Representation Process

Differential data is mapped to XSLT templates

and a differential XSLT stylesheet is generated from

them.

The following subsections describe these

processes in detail.

2.1 Difference Detection Process

In the first step, accordant, appearing and

disappearing nodes are detected. We propose a new

detection algorithm that changes the DOM tree

structures, maximizes the accordant tree and regards

the remaining nodes as differential nodes. The

assumptions of the algorithm are as follows.

i) A virtual node is assumed at the head of an

actual root node and regarded as a temporary root

node. It is treated as a common node. (Fig. 2)

ii) The goal is to maximize the number of

common nodes.

iii) The term “common” means that the nodes

have the same element names, same attribute names,

and same attribute values.

Note that it is not necessary to compare an

element node, an attribute node and a text node if

they are treated as DOM nodes. Nodes are compared

type-by-type for efficiency.

The proposed difference detection method is

described below with reference to Fig. 4 using the

XML document in Fig. 3.

(a) Finding maximum number of common nodes

(Fig. 4(a))

The method compares the components of the

DOM trees to find the maximum number of

common nodes.

(b) Creating combination of nodes and comparing

DOM tree structures (Fig. 4(b))

Combinations are compared in decreasing order

of the number of nodes.

and disappearing nodes (Fig. 4(c))

The node-set in the DOM tree that has the

maximum number of accordant nodes, are regarded

as determinate accordant node-set. Other nodes in

the DOM trees than determinate accordant node-set

are taken to be the determinate differential nodes,

which are then classified into two types, appearing

nodes and disappearing node. Appearing nodes are

the determinate differential nodes in the original

DOM tree. Disappearing nodes are the determinate

differential nodes in the updated DOM tree. The

information of each node is arranged into three

tables. In the accordant node table, “Reference

position” column indicates the position of each

accordant node. “Original position” column means

the position of the accordant node in the original

DOM tree and “Updated position” column similarly

indicates the position in the updated DOM tree. In

the appearing node table, “appearance position”

column indicates the position in the updated DOM

tree. “Absolute position” column means the relative

position of correspondent node in the accordant

DOM tree. In the disappearing node table,

“disappearance position” column indicates the

Figure 1: Generation Process of Differential

XSLT Stylesheet.

Figure 2: Structure of XML Document.

Figure 3: Example of original and updated XML

Document.

Original

XML

Document

Original

XML

Document

Updated

XML

Document

Updated

XML

Document

Step-1

Difference

Detection

Process

Step-1

Difference

Detection

Process

Step-2

Difference

Extraction

Process

Step-2

Difference

Extraction

Process

Step-3

Difference

Representation

Process

Step-3

Difference

Representation

Process

Original DOM Tree

Updated DOM Tree

Differential

Information

Differential

Information

Differential

XSLT

Stylesheet

Differential

XSLT

Stylesheet

Parsing

XML

ABC

ABC

</RouteElement>

ABC

</RouteElement>

...Root Node

...Element Node

...Text NodeXML Document

<A>

<F/>

<C/>

<D/>

</A>

<A>

<F/>

<C/>

<D/>

</A>

<A>

<2/>

<1>

<F/>

<C/>

</1>

</A>

<A>

<2/>

<1>

<F/>

<C/>

</1>

</A>

Original XML Document Updated XML Document

WEBIST 2005 - INTERNET COMPUTING

position in the original DOM tree. “Absolute

position” column similarly means the relative

position of correspondent node in accordant DOM

tree. In each table, other nodes than accordant nodes

are represented using node[n] in which n is a

position in the same siblings in the updated DOM

tree. A leftmost node is expressed as node[1].

Attribute nodes are expressed as @ + attribute

name.

The purpose of this process is to detect the

maximum number of accordant nodes and the

remaining differential nodes.

2.2 Difference Extraction Process

In this step, detailed differential data is extracted

from the tables created in the previous step. The

proposed method classifies appearing and

disappearing nodes into three kinds of nodes.

i) Change node

Comparing an appearing node table and a

disappearing node table, two nodes that have the

same absolute position and the same type are

regarded as change nodes. In Fig. 4, node “2” in the

appearing node table and node “F” in the

disappearing node table are change nodes.

ii) Added node

Other nodes than change nodes in an appearing

node table are regarded as added nodes. In Fig. 4,

node “1” and node “F” in the appearing node table

are added nodes.

iii) Deleted node

Other nodes than change nodes in a disappearing

node table are regarded as deleted nodes. In Fig. 4,

node “D” in the disappearing node table is a deleted

node.

Fig. 5 shows a table of differential nodes created

from the XML documents in Fig. 3.

2.3 Difference Representation Process

In this step, differential data generated in the

previous step are mapped to XSLT templates from

which a differential XSLT stylesheet is generated.

The proposed difference representation method

consists of the following sequences.

(a) Determining a transformation position as a

pattern of XSLT template rule

A XML data structure transformation is

described specifying the following two items.

- Which position of XML data is transformed?

(Determining a transformation position as a pattern

of XSLT template rule)

- How is the corresponding part of XML data

transformed? (Transformational description)

Figure 5: Example of Differential nodes.

Figure 6: XSLT Template rule.

Figure 4: Difference Detection Process.

Original XML Updated XML

ABCDEF ABC 1EF 2

A B C E F A B C E F

(a) Finding maximum number of common nodes

ABCE ABCE

(b) Creating combination of nodes and comparing DOM tree structures

CB D

E F

B 1

E 2 F C

CB D

E F

B 1

E 2 F C

/A/B/A/B/A/B-BElement

/A/node[2]/C/A/C/A/C-CElement

/A/B/@E/A/B/@E/A/B/@E“X”EAttribute

Updated

position

Original

position

Reference

position

Value

NodeName

Element

NodeType

/A/B/A/B/A/B-BElement

/A/node[2]/C/A/C/A/C-CElement

/A/B/@E/A/B/@E/A/B/@E“X”EAttribute

Updated

position

Original

position

Reference

position

Value

NodeName

Element

NodeType

/A/node[1]

/A/B/node[1]

/A/node[2]

Absolute position

/A/node[2]/node[1]-FElement

/A/B/node[1]

/A/node[2]

Appearance position

Value

NodeName

Element

NodeType

/A/node[1]

/A/B/node[1]

/A/node[2]

Absolute position

/A/node[2]/node[1]-FElement

/A/B/node[1]

/A/node[2]

Appearance position

Value

NodeName

Element

NodeType

/A/B/node[1]

/A/node[3]

Absolute Position

/A/B/node[1]

/A/node[3]

Disappearance position

Value

NodeName

Element

NodeType

/A/B/node[1]

/A/node[3]

Absolute Position

/A/B/node[1]

/A/node[3]

Disappearance position

Value

NodeName

Element

NodeType

Accordant node table

Appearing node table

Disappearing node table

ABCEF ABCEF

ABCF ABCF

ABEF ABEF

Accordance

-1ElementAdditionElement/A/*[2]

-2Element

ChangeElement/A/B/*[1]

DeletionElement/A/*[3]

AdditionElement/A/*[2]/*[1]

Node

Value

Node

Name

Node

Type

Element

Additional Data

Classification

of difference

Node

Type

Reference

Position

-1ElementAdditionElement/A/*[2]

-2Element

ChangeElement/A/B/*[1]

DeletionElement/A/*[3]

AdditionElement/A/*[2]/*[1]

Node

Value

Node

Name

Node

Type

Element

Additional Data

Classification

of difference

Node

Type

Reference

Position

<xsl:template match=“ ”>

</xsl:template>

<xsl:template match=“ ”>

</xsl:template>

Pattern

Transformational description

Original XML Updated XML

/A/B

<xsl:copy>

<X/>

</xsl:copy>

<xsl:copy>

<X/>

</xsl:copy>

Node X is a

child of Node B

Added Node

Accordant Node

Relative position

Absolute position

AN AUTOMATIC GENERATION METHOD OF DIFFERENTIAL XSLT STYLESHEET FROM TWO XML

DOCUMENTS

These items constitute a template rule and are

represented as xsl:temlate element in the XSLT

stylesheet. (Fig. 6) In a template rule, a pattern is an

XPath[Clark, 1999] expression of the position of a

node in an original DOM tree. We must specify

transformation position as a pattern in a template

rule. The position of an added node in an updated

DOM tree is separated into a reference position and

relative position and the reference position is

specified as a pattern in a template rule.

In the proposed method, a pattern of a template

rule is determined by tracing an updated DOM tree

from top to bottom (from a parent to a child), and

from left to right (from an elder brother to a younger

brother) As a result, templates are generated in a tree

structure that branch toward the descendant

direction. Additionally, the positions of change and

accordance nodes can be used as a pattern of a

template rule because their own position can be

specified in an original DOM tree. The method used

to determine a pattern of a template rule is described

with reference to Fig. 8. For change nodes and

accordance nodes, their own positions are patterns.

In case of added nodes, patterns are determined

according to following sequences.

i) Searching a pattern toward descendant nodes

(Fig.7 (a))

A change node or an accordance node is

searched for starting from the corresponding node

and moving toward descendant nodes. The position

of the nearest descendant appropriate node is

regarded as a pattern. If there is no appropriate node,

there are multiple appropriate nodes, or there is a

branch in the tree, the next procedure is applied.

ii) Searching a pattern toward elder brother nodes

(Fig. 7(b)

A change node or an accordance node is

searched starting from the corresponding node and

moving toward elder brother nodes. The position of

the nearest elder brother appropriate node is

regarded as a pattern. If there is no appropriate node,

the next procedure is applied.

iii) Searching a pattern toward younger brother

nodes (Fig. 7(c))

A change node or an accordance node is

searched starting from the corresponding node

toward younger brother nodes. The position of the

nearest younger brother appropriate node is regarded

as a pattern. If there is no appropriate node, the next

procedure is applied.

iv) Searching a pattern toward ancestor nodes

(Fig. 7(d))

A change node or an accordance node is

searched from the corresponding node toward

ancestor nodes. The position of the nearest ancestor

appropriate node is regarded as a pattern. If there is

no appropriate node, the pattern of a parent node is

taken as that of the corresponding node.

The reason why the search pattern direction

begins with descendant nodes and leaves ancestor

nodes to the last is that if a pattern search

commences with ancestor nodes, a pattern is

underspecified since XML has a tree structure.

The search process for deleted nodes starts with

ancestor nodes. As shown in Fig. 8, if all descendant

nodes are deleted nodes, the position of the top node

is regarded as the pattern of these nodes and all

deleted nodes can be deleted using the same

template. Therefore, the position of the farthest

ancestor node which has only deleted nodes is

regarded as the pattern. If there is no appropriate

node, the position of the corresponding node is

regarded as the pattern.

The search for attribute nodes also starts toward

ancestor nodes, because attribute nodes basically

have only parent nodes.

Figure 7: Searching a transformation position as a

pattern of XSLT template rule.

Figure 8: Searching pattern of deletion node.

potential pattern node

(Accordant node / change node)

Added node

Node A is a

pattern of both

Node 1 and 2

Node A is a pattern

of Node 1

32 4 21 3

Node A is a pattern of both

Node 2 and 3.

Node B is a pattern of Node 4

Node B is a patter of both

Node 1and 2

Node C is a patter of Node 3

(a) Searching a pattern toward descendant nodes

(b) Searching a pattern toward elder brother nodes

Node A is a

pattern of both

Node 2 and 3

Node A is a

pattern of both

Node 1 and 2

Node A is a

patter of Node 1

Node A is a patter

of both Node 1 and

(d) Searching a pattern toward ancestor nodes

3 4

Node 3 has only

deleted node as its own

descendant node

Node 3Node 6

Node 3Node 5

Node 4Node 4

Node 3Node 3

Node 2Node 2

Node 1

Pattern

Node 1

Node Name

Node 3Node 6

Node 3Node 5

Node 4Node 4

Node 3Node 3

Node 2Node 2

Node 1

Pattern

Node 1

Node Name

potential pattern node

(Accordant node / change node)

Deleted node

<xsl:template match=“/A/1/2/3”>

<xsl:template>

<xsl:template match=“/A/1/2/3”>

<xsl:template>

Template rule for deleting Node 3,5 and 6

WEBIST 2005 - INTERNET COMPUTING

(b) Generating mapping information

Differential data is organized according to the

patterns identified in the previous step. The

differential nodes are classified according to pattern

because differential nodes that have the same pattern

can be described using the same XSLT template.

Fig. 9 shows the differential data for the XML

documents in Fig. 3.

Differential data is mapped to an XSLT template

according to node type and classification of

difference.

i) Mapping to XSLT template for accordant,

changed and deleted nodes

Nodes that have the same pattern are collectively

described by the same XSLT template. As shown in

Appendix A at the end of this paper, each node is

mapped to one XSLT template.

ii) Mapping to XSLT template for added nodes

Nodes that have the same pattern are collectively

described by the same XSLT template. The added

node is described as Appendix B. If a node regarded

as a pattern has a descendant template, xsl:apply-

template element is added in correspond template. If

a node which share the same pattern are described

by the same template. If there are multiple

descendant templates of the correspond added node,

multiple xsl:apply-template elements are used as

shown in Appendix C.

Fig. 10 shows XSLT templates for the XML

documents in Fig. 3.

(d) Generating a differential XSLT stylesheet

A Differential XSLT stylesheet is generated

from XSLT templates as shown in Fig. 11. The

header part includes a XML declaration and various

XSLT parameters. The footer part includes a

template to copy those accordance nodes that are not

regarded as transformation position (pattern node).

3 EXPERIMENTS

We have implemented prototype software in Java

(J2SE 1.3.1).We used Apache Xalan-Java 2.4.0

(XSLT Engine) to verify the generated XSLT

stylesheets and IBM XML Parser for Java to parse

XML documents. Our prototype software has

functions to generate differential XSLT stylesheets

from arbitrary pairs of XML documents and verify

them. Additionally, it provides a graphical viewer of

the differential data of two XML documents and

shows some values such as compression ratio,

difference ratio and so on. We have examined the

validity of our proposed method using this software.

3.1 Stock Price Information

We have investigated the relationship between

compression ratio and difference ratio using the

following stock price information. In Fig. 12, stock

price is updated every minute; old price data are

Figure 10: Example of XSLT Templates.

Figure 11: Differential XSLT Stylesheet.

Figure 9: Differential Information according to

Patterns.

YesChangeElement/A/B/F

Yes

Accordance

Element/A/B

Yes

Accordance

Element/A/C

Yes

Transfor

mation

Accordance

Deletion

Accordance

Difference

Attribute

Element

Node

Type

/A/D

/A/E

Absolute

position

YesChangeElement/A/B/F

Yes

Accordance

Element/A/B

Yes

Accordance

Element/A/C

Yes

Transfor

mation

Accordance

Deletion

Accordance

Difference

Attribute

Element

Node

Type

/A/D

/A/E

Absolute

position

/A/D

/A/C

/A/B/F

/A/B

Pattern

Deletion/A/D

Addition/A/1/F

Change/A/B/2

Addition/A/1

Difference

Node

Name

/A/D

/A/C

/A/B/F

/A/B

Pattern

Deletion/A/D

Addition/A/1/F

Change/A/B/2

Addition/A/1

Difference

Node

Name

Pattern node table

---DeletionElementitself/A/D

-2ElementChangeElementitself/A/B/F

Elder

brother

Parent

Relative

position

Node

Value

Node

Name

Node

Type

Element

Addition Data

Addition

Difference

Element

Node

Type

/A/C

/A/B

Absolute

position

---DeletionElementitself/A/D

-2ElementChangeElementitself/A/B/F

Elder

brother

Parent

Relative

position

Node

Value

Node

Name

Node

Type

Element

Addition Data

Addition

Difference

Element

Node

Type

/A/C

/A/B

Absolute

position

Pattern of template rule

Transformational description of template rule

Before XML After XML

CB D

E F

B 1

E 2 F C

<xsl:template match="/node()[1]/node()[1]">

<xsl:copy>

<xsl:apply-templates />

</xsl:copy>

<Node1>

<xsl:apply-templates select="/node()[1]/node()[2]" />

</Node1>

</xsl:template>

Copy of Node B and addition of Node 1

<xsl:template match="/node()[1]/node()[2]">

<F/>

<xsl:copy>

</xsl:copy>

</xsl:template>

Copy of Node C and addition of Node F

<xsl:template match="/node()[1]">

<xsl:copy>

<xsl:apply-templates select="/node()[1]/node()[1]" />

</xsl:copy>

</xsl:template>

Copy of Node A

<xsl:template match="/node()[1]/node()[3]">

</xsl:template>

Deletion of Node D

<xsl:template match="/node()[1]/node()[1]/node()[2]">

</xsl:template>

Change of Node F to Node 2

<?xml version=“1.0” encoding=“Shift_JIS”?>

<xsl:stylesheet version=“1.0” xmlns:xsl=http://www.w3.org/1999/XSL/Transform>”

<xsl:output method=“xml” omit-xml-declaration=“no” version=“1.0”

encoding=“Shift_JIS” indent=“no” doctype-system=“i-xhtml10.dtd”

doctype-public=“-//NTT DoCoMo//XHTML DTD i-XHTML 1.0//EN”/>

<?xml version=“1.0” encoding=“Shift_JIS”?>

<xsl:stylesheet version=“1.0” xmlns:xsl=http://www.w3.org/1999/XSL/Transform>”

<xsl:output method=“xml” omit-xml-declaration=“no” version=“1.0”

encoding=“Shift_JIS” indent=“no” doctype-system=“i-xhtml10.dtd”

doctype-public=“-//NTT DoCoMo//XHTML DTD i-XHTML 1.0//EN”/>

<xsl:template match=“@*|node()”>

<xsl:copy>

<xsl:apply-templates select=“@*|node()”/>

</xsl:copy>

</xsl:template>

</xsl:stylesheet>

<xsl:template match=“@*|node()”>

<xsl:copy>

<xsl:apply-templates select=“@*|node()”/>

</xsl:copy>

</xsl:template>

</xsl:stylesheet>

XSLT template

Header

Footer

Difference Data

AN AUTOMATIC GENERATION METHOD OF DIFFERENTIAL XSLT STYLESHEET FROM TWO XML

DOCUMENTS

deleted and new price data are added. We changed

XML data size and differential ratio and determined

the resulting compression ratio.

The compression ratio is defined as the ratio of

generated XSLT stylesheet to the before XML data.

The difference ratio is defined rate of existence of

unique nodes. (See formula (1) and (2).)

Fig. 13 shows the experimental result using

stock price information. In our experiments, the size

of a XML document was changed from 1Kbyte to

100Kbyte, the difference ratio was changed from

about 4% to 50%. As shown in Fig. 13, compression

ratio becomes high when the size of a XML

document increases. This means that the overhead of

the header and footer of the XSLT stylesheet can be

decreased for a large XML document. Even a small

XML document (i.e. 1Kbyte document) can be

effectively compressed if the difference ratio is

below 25%. Therefore, the proposed method is

suitable even for a small XML document if it has

only minor updates.

3.2 News Flash Content

Then we have investigated the relationship between

actual compression ratio and difference ratio using

the following news flash content. In Fig. 14, news

flash is updated; an old item is deleted and a new

item is added. We changed difference ratio and

compared the compression ratio of a differential

XSLT stylesheet (D-XSLT), a differential XSLT

stylesheet compressed by gzip (D-XSLT+gzip), a

Diff [GNU, 2002] file compressed by gzip

(Diff+gzip) and an entirely updated content

compressed using gzip (HTML+gzip).

Fig 15 shows the experimental result. The

difference ratio is changed from about 10% to 45%.

As shown in Fig. 15, a differential XSLT stylesheet

complessed by gzip (D-XSLT+gzip) reduces about

63% of the size of entirely updated content

compressed by gzip. Compared to Diff file

compressed by gzip (Diff+gzip), the size of D-

XSLT+gzip is about 38% larger. This result shows,

although the proposed method is not optimised

compared with Diff+gzip method, it realizes

comparatively efficient compression.

Figure 12: XML data of intra-day chart.

(%) 100

data XML updated of Size

Stylesheet XSLT Generated of Size

ration Compressio ×=

(1)

(%) 100

document XML updatedin nodes all ofNumber

nodes ediscordanc ofNumber

ratio Difference ×=

(2)

Figure 13: Relationship between compression ratio

and difference ratio using stock price information.

Figure 14: News Flash Content.

Figure 15: Relationship between compression ratio

and difference ratio using news flash content.

<?xml version="1.0"

encoding="UTF-16" ?>

<Price>

</Price>

</Company>

</StockData>

<?xml version="1.0"

encoding="UTF-16" ?>

<Price>

</Price>

</Company>

</StockData>

addition

Original XML Data

Updated XML Data

Deletion

100

120

140

0 102030405060

Difference Ratio (%)

Compression Ratio (%)

10K

50K

100K

addition

Original News Content Updated News Content

Deletion

100

120

0 1020304050

Difference Ratio (%)

Compression Ratio (%)

D-XSLT

D-XSLT+gzip

Diff+gzip

HTML+gzip

WEBIST 2005 - INTERNET COMPUTING

4 EXTENSION TO XSLT

FUNCTIONS

XSLT is not optimized for generating differential

XSLT stylesheets. We have considered new XSLT

function for the proposed method as described

below.

i) Package copy of element and attribute nodes

In Fig. 16, node “e1” is entirely copied under the

node “e3”. However, XSLT can not copy any

particular node. Thus the XSLT template repeats the

same data of node “e1”. The XSLT template must

have the same data contained in the original XML

document. This decreases the efficiency of

compression.

ii) Range copy

In Fig. 17, a sub-tree consists of the node “e1”

and the node “e2”, is copied under the node “e4”. In

XSLT, a sub-tree can be regarded as a node-set

using xsl:copy-of element. However a node-set must

include all nodes under the root of a sub-tree. Thus a

node-set cannot be used to designate some parts of a

sub-tree. Some parts of a sub-tree can not be copied

using xsl:copy-of element.

We propose a new XSLT function for xsl:copy-

of element that designates nodes from the root of a

sub-tree to the n-th generation descendants. If the

proposed function is applied to above two examples,

the resulting XSLT templates are generated as

shown in Fig 18.

Introducing such a function can optimize the

generation of a differential XSLT stylesheet.

5 RELATED WORK

Compared to existing methods of differential data

generation [La Fontaine, 2001][Curbera, 1999], the

proposed method has the advantage of easily

adapting to expanded data as XML tree, and using

existing XSLT engines. But there is a problem that

mobile terminals have to deal with heavy process to

expand XML navigation tree into memory. To

lighten this process, XML processors for mobile

terminals such as TinyTree[OSTG, 2004b] and

DTM (Document Table Model)[Apache Project,

2004] have been developed. By expanding XML

document as tree or array structure in the memory

using these XML processors, it is more efficient to

deal with difference data. In addition, the proposed

method needs only XSLT engine, different from

DUL (Delta Update Language) [OSTG 2004a] in

which special language processing module is

needed.

La Fontaine (2001) and Curbera (1999)

described methods to generate difference data from

arbitrary pairs of XML documents. These methods

compare nodes of the original and the revised XML

DOM trees from root to leaf. If a unique node is

detected, all descendant nodes from that node are

regarded as difference. They can not detect the most

appropriate difference and no mention was made of

this issue. On the other hand, the proposed method

resolves this issue and so can extract the differences

most effectively. It similarly compares the nodes of

the original and revised XML DOM trees from root

to leaf. When a unique node is detected, the

corresponding node is regarded as difference if its

descendant nodes are common. Therefore it is able

to accurately detect the difference between original

and revised XML documents.

6 CONCLUSION

We proposed an automatic method of generating

differential XSLT stylesheets from arbitrary pairs of

Figure 16: Example 1 of XSLT Stylesheet.

Figure 17: Example 2 of XSLT Stylesheet.

Figure 18: Example of XSLT template using

proposed function.

<root>

<e2/>

</e1>

<e3/>

</root>

<root>

<e2/>

</e1>

<e3/>

</root>

Original XML Data

Updated XML Data

<xsl:temlate match=“e3”>

<xsl:copy>

</xsl:copy>

</xsl:template>

<xsl:temlate match=“e3”>

<xsl:copy>

</xsl:copy>

</xsl:template>

XSLT template

<root>

<e2/>

</e1>

<e3>

</e3>

</root>

<root>

<e2/>

</e1>

<e3>

</e3>

</root>

<root>

<e4/>

</root>

<root>

<e4/>

</root>

Original XML Data

Updated XML Data

<xsl:temlate match=“e4”>

<xsl:copy>

<e1>

<e2/>

</e1>

</xsl:copy>

</xsl:template>

<xsl:temlate match=“e4”>

<xsl:copy>

<e1>

<e2/>

</e1>

</xsl:copy>

</xsl:template>

XSLT template

<root>

<e4>

<e1>

<e2/>

</e1>

</e4>

</root>

<root>

<e4>

<e1>

<e2/>

</e1>

</e4>

</root>

<xsl:temlate match=“e3”>

<xsl:copy>

<xsl:copy-of select=“/e1[generation()=0]”>

</xsl:copy>

</xsl:template>

<xsl:temlate match=“e3”>

<xsl:copy>

<xsl:copy-of select=“/e1[generation()=0]”>

</xsl:copy>

</xsl:template>

<xsl:temlate match=“e4”>

<xsl:copy>

<xsl:copy-of select=“/e1/node()[generation()=1]”>

</xsl:copy>

</xsl:template>

<xsl:temlate match=“e4”>

<xsl:copy>

<xsl:copy-of select=“/e1/node()[generation()=1]”>

</xsl:copy>

</xsl:template>

Example 1 of XSLT Stylesheet

Example 2 of XSLT Stylesheet

AN AUTOMATIC GENERATION METHOD OF DIFFERENTIAL XSLT STYLESHEET FROM TWO XML

DOCUMENTS

XML documents. The proposed method consists of

difference detection, difference extraction and

difference representation; we proposed algorithms

for each process. We have implemented prototype

software and showed it to be effective using special

contents such as stock price and news flash. We also

proposed new XSLT function.

In future work, we will investigate processing

time to generate differential XSLT stylesheet and

continue to work on improving the performance of

our algorithm. Future work includes quantitatively

evaluating the proposed method in the case of

general XML content. We will also confirm the

effectiveness of the proposed XSLT function.

REFERENCES

Bray, T. el al (2000) Extensible Markup Language (XML)

1.0 (Second Edition). W3C Recommendation.

Baker, M. et al (2000) XHTML Basic. W3C

Recommendation.

Mogul, Jeffrey C. et al (1997) Potential benefits of delta-

encoding and data compression for HTTP. Proceeding

of SIGCOMM 97. SIGCOMM 97.

Mogul, Jeffrey C. et al (2002) Delta Encoding in HTTP.

RFC3229. The Internet Engineering Task Force.

Clark, J. (2000) XSL Transformations (XSLT) Version 1.0.

W3C Recommendation.

Le Hors, A. et al (2000) Document Object Model (DOM)

Level 2 Core Specification Version 1.0. W3C

Recommendation.

Clark, J. (1999) XML Path Language (XPath) Version 1.0.

W3C Recommendation.

The GNU Project (2002) Diffutils [Software]. Version

2.8.1. www.gnu.org. Available from:

<http://directory.fsf.org/GNU/diffutils.html>

[Accessed 25 January 2005].

Open Source Technology Group (2004a) diffxml

[software]. Version 0.92A. SourceForge.net. Available

from: <http://diffxml.sourceforge.net/> [Accessed 25

January 2005].

Open Source Technology Group (2004b) SAXON

[software]. version 8.2. SourceForge.net. Available

from: <http://saxon.sourceforge.net/> [Accessed 25

January 2005].

The Apache Software Foundation (2004) xalan-J

[software] version 2.6.0. www.apache.org. Available

from:

<http://www.apache.org/dyn/closer.cgi/xml/xalan-j>

[Accessed 25 January 2005].

La Fontaine, R. (2001) A Delta Format for XML:

Identifying Changes in XML Files and Representing

the Change in XML. XML Europe 2001.

Curbera, F. P. et al (1999) Fast Difference and Update of

XML Documents. XTech'99 held in San Jose.

Ishikawa, N. et al (2002) Automatic Generation of a

Differential XSL Stylesheet From Two XML

Documents. Proceeding of WWW Conference 2002

held in Hawaii. WWW Conference 2002.

Appendix A: XSLT template mapping for

accordance, delete and change node.

Appendix B: XSLT template mapping for addition

node

Appendix C: XSLT template mapping for addition

node with

descendant

templates

<xsl:template match=“XPath of a

pattern node”>

<xsl:copy>

<xsl:apply-templates/>

</xsl:copy>

</xsl:template>

<xsl:template match=“XPath of a

pattern node”>

<xsl:copy/>

<Younger brother addition

node/>

</xsl:template>

Addition

node in

younger

brother

<xsl:template match=“XPath of a

pattern node”>

<xsl:copy>

<xsl:apply-templates/>

</xsl:copy>

</xsl:template>

<xsl:template match=“XPath of a

pattern node”>

<xsl:copy/>

</xsl:template>

Addition

node in

elder

brother

Addition

node in

Child

Same as left template<xsl:template match=“XPath of a

pattern node”>

<xsl:copy>

</xsl:copy>

</xsl:template>

<xsl:template match=“XPath of a

pattern node”>

<xsl:copy/>

</Parent addition node>

</xsl:template>

Mapping to XSLT

(No continuing process to

descendant of pattern)

<xsl:template match=“XPath of its

own position”>

<xsl:copy>

<xsl:apply-template>

</xsl:copy>

</Parent addition node>

</xsl:template>

Addition

node in

Parent

Mapping to XSLT

(Continuing process to

descendant of pattern)

TYPE

<xsl:template match=“XPath of a

pattern node”>

<xsl:copy>

<xsl:apply-templates/>

</xsl:copy>

</xsl:template>

<xsl:template match=“XPath of a

pattern node”>

<xsl:copy/>

<Younger brother addition

node/>

</xsl:template>

Addition

node in

younger

brother

<xsl:template match=“XPath of a

pattern node”>

<xsl:copy>

<xsl:apply-templates/>

</xsl:copy>

</xsl:template>

<xsl:template match=“XPath of a

pattern node”>

<xsl:copy/>

</xsl:template>

Addition

node in

elder

brother

Addition

node in

Child

Same as left template<xsl:template match=“XPath of a

pattern node”>

<xsl:copy>

</xsl:copy>

</xsl:template>

<xsl:template match=“XPath of a

pattern node”>

<xsl:copy/>

</Parent addition node>

</xsl:template>

Mapping to XSLT

(No continuing process to

descendant of pattern)

<xsl:template match=“XPath of its

own position”>

<xsl:copy>

<xsl:apply-template>

</xsl:copy>

</Parent addition node>

</xsl:template>

Addition

node in

Parent

Mapping to XSLT

(Continuing process to

descendant of pattern)

TYPE

<xsl:apply-template select=“XPath of

lower pattern”/>

</Addition node>

Mapping to XSLT

(No continuing process to

descendant of addition node)

Additio

n node

Mapping to XSLT

(Continuing process to descendant

of addition node)

TYPE

<xsl:apply-template select=“XPath of

lower pattern”/>

</Addition node>

Mapping to XSLT

(No continuing process to

descendant of addition node)

Additio

n node

Mapping to XSLT

(Continuing process to descendant

of addition node)

TYPE

<xsl:template match=“XPath of its

own position”>

<xsl:apply-templates/>

</Data of Changed node>

</xsl:template>

<xsl:template match=“XPath of

its own position”>

</xsl:template>

Change

<xsl:template match=“XPath of its

own position”>

<xsl:apply-templates/>

</xsl:template>

<xsl:template match=“XPath of

its own position”>

</xsl:template>

Delete

No template

Mapping to XSLT

(No continuing process to

descendant of pattern)

<xsl:template match=“XPath of its

own position”>

<xsl:copy>

<xsl:apply-templates/>

</xsl:copy>

</xsl:template>

Accordance

Mapping to XSLT

(Continuing process to

descendant of pattern)

TYPE

<xsl:template match=“XPath of its

own position”>

<xsl:apply-templates/>

</Data of Changed node>

</xsl:template>

<xsl:template match=“XPath of

its own position”>

</xsl:template>

Change

<xsl:template match=“XPath of its

own position”>

<xsl:apply-templates/>

</xsl:template>

<xsl:template match=“XPath of

its own position”>

</xsl:template>

Delete

No template

Mapping to XSLT

(No continuing process to

descendant of pattern)

<xsl:template match=“XPath of its

own position”>

<xsl:copy>

<xsl:apply-templates/>

</xsl:copy>

</xsl:template>

Accordance

Mapping to XSLT

(Continuing process to

descendant of pattern)

TYPE

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