use of attribute grammars to construct xml translators supervisor: prof. john hurst presenter:...

Use of Attribute Grammars to Construct XML translators

Supervisor: Prof. John HurstSupervisor: Prof. John Hurst

Presenter: Nishan Jayasinghe Presenter: Nishan Jayasinghe

Project AimProject Aim

Existing XML Translator XSLTExisting XML Translator XSLT

Translator Writing TechniquesTranslator Writing Techniques

The Translators & Difficulties Encountered The Translators & Difficulties Encountered

What Was Learnt?What Was Learnt?

Future Work and ConclusionFuture Work and Conclusion

Overview

Project Aim Can we translate XML using attribute grammars?Can we translate XML using attribute grammars?

Is it simpler to translate XML with attribute Is it simpler to translate XML with attribute grammars compared to existing solutions?grammars compared to existing solutions?

Is it possible to create a simpler specification Is it possible to create a simpler specification language that represent attribute grammar language that represent attribute grammar computations?computations?

Existing XML Translator Most popular method for translating XML is XSLT Most popular method for translating XML is XSLT XML document and specification are used by XSL XML document and specification are used by XSL

processor to do the translationprocessor to do the translation

AdvantagesAdvantages Disadvantages Disadvantages Simple to update and Simple to update and maintain the XSLT maintain the XSLT specificationsspecifications Reuse specification using Reuse specification using by including other by including other specificationsspecifications

XSLT sXSLT specification pecification syntax is complicatedsyntax is complicated

Translator Writing Techniques

Subset of stages involved in constructing a compilerSubset of stages involved in constructing a compiler Lexical AnalysisLexical Analysis Syntax AnalysisSyntax Analysis Semantic AnalysisSemantic Analysis

Why use these techniques?Why use these techniques? These techniques have been applied to other These techniques have been applied to other

translator writing taskstranslator writing tasks Development time and effort shorterDevelopment time and effort shorter

Lexical Analysis

Break up input document into tokensBreak up input document into tokens Using Regular ExpressionUsing Regular Expression

<name> XML for Beginners </name><name> XML for Beginners </name>

StartName : <name>StartName : <name>

DATA :DATA : [A-Za-z]+[A-Za-z]+

EndName : </name>EndName : </name>

Syntax Analysis

Describes the document structureDescribes the document structure Using Context Free GrammarUsing Context Free Grammar

<book><book>

<name> XML for Beginners </name><name> XML for Beginners </name>

<author> J. Smith </author><author> J. Smith </author>

</book></book>

book: startBook name author endBook .book: startBook name author endBook .

name: startName DATA endName .name: startName DATA endName .

author: startAuthor DATA endAuthor .author: startAuthor DATA endAuthor .

Semantic Analysis Describes computations that should occur given a Describes computations that should occur given a

particular contextparticular context Using Attribute GrammarUsing Attribute Grammar

<name> XML for Beginners </name> <name> XML for Beginners </name>

Title: XML for BeginnersTitle: XML for Beginners UsingUsing

RULE: name ::= startName DATA endName COMPUTERULE: name ::= startName DATA endName COMPUTE

name.output = Concatenate( “Title:”, name.output = Concatenate( “Title:”, DATA);DATA);

END; END;

Input

(XML document)

Lexical Analysis Syntax Analysis Semantic Analysis

Output

(translated document)

Document Processing

The Translators

It is possible to translate XML documentsIt is possible to translate XML documents Created two translatorsCreated two translators

XML to HTMLXML to HTML

XML to TEXXML to TEX

Our HTML Translator Output

XSLT Output

Our TEX Translator Output

XSLT Output

Display On a web browser

Difficulties Encountered We found that the translators can not deal with the We found that the translators can not deal with the

following XSLT featuresfollowing XSLT features White space characters outside the character White space characters outside the character

data sections data sections

Changing of document structure from input Changing of document structure from input documentdocument

Length and complexity of CodeLength and complexity of Code

Code Size Example

XSLT Counting

<xsl:template match="enumerate"> <xsl:variable name=“depth" select="count(ancestor::enumerate)"/></xsl:template>

Attribute Grammar

ATTR depth: int INH;

RULE: document ::= DocType article COMPUTE document.depth = 0;END;

SYMBOL enumerate COMPUTE INH.depth = ADD(INCLUDING (enumerate.depth,document.depth), 1);END;

What Did We Learn? Writing Attribute Grammar translator is very time Writing Attribute Grammar translator is very time

consuming compared with XSLTconsuming compared with XSLT Difficult to learn some conceptsDifficult to learn some concepts The amount of code required for simple The amount of code required for simple

translator is not worth the efforttranslator is not worth the effort

But is possible to automatically generate (given But is possible to automatically generate (given the DTD) specifications using a simple algorithm the DTD) specifications using a simple algorithm forfor Lexical Analysis specificationLexical Analysis specification Syntax Analysis specificationSyntax Analysis specification

Algorithm for DTD to Lexical Specifications

<!ELEMENT book (name, author)><!ELEMENT book (name, author)>

<!ELEMENT name (#PCDATA)><!ELEMENT name (#PCDATA)>

<!ELEMENT author (#PCDATA)><!ELEMENT author (#PCDATA)>

Lexical Tokens

startBook : <book>

endBook : </book>

startName : <name>

endName : </name>

startAuthor : <author>

endAuthor : </author>

PCDATA : [A-Za-z]+

Algorithm for DTD to Syntax Specifications

<!ELEMENT book (name, author)><!ELEMENT book (name, author)>

<!ELEMENT name (#PCDATA)><!ELEMENT name (#PCDATA)>

<!ELEMENT author (#PCDATA)><!ELEMENT author (#PCDATA)>

Context Free Grammar

book : startBook name author endBook

name : startName PCDATA endName

author : startAuthor PCDATA endAuthor

Future Work Due to a lack of timeDue to a lack of time we could not create a we could not create a

specification language that can be used instead specification language that can be used instead of attribute grammars by usersof attribute grammars by users

Implement other XSLT functions such as sortImplement other XSLT functions such as sort

Try extending the automatic generation of Try extending the automatic generation of specifications to other types of document specifications to other types of document formatsformats

Conclusion We were able to translate XML documents using We were able to translate XML documents using

attribute grammarsattribute grammars

We were able to reduce most of the time required We were able to reduce most of the time required for developing attribute grammar translator using for developing attribute grammar translator using automatically generated specificationsautomatically generated specifications

It is clear at the moment XSLT is much simpler It is clear at the moment XSLT is much simpler specification language from writing translations specification language from writing translations