9/25/08 IEEE ICWS 2008

High-Performance XML Parsing and Validation with Permutation Phrase Grammar Parsers

Wei Zhang & Robert van Engelen

Department of Computer Science

Florida State University

IEEE ICWS 2008 29/25/08

Presentation Overview

Schema-specific Parsers Related Work PTDX: Table-Driven XML Parser with

Permutation Phrase Grammar Performance Conclusion

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Schema-specific parsers Compile-time vs. Run-time Parsers

Compile-time parsing and validation approaches use specialized compilation techniques to generate customized parsers from schemas

Run-time approaches use generic drivers( or engines) and grammar-like representation of schemas

Blocking vs. non-blocking Parsers Blocking parsers may suspend the entire program for sufficient

XML content received. E.g. recursive based parsers Non-blocking parsers always control the program and buffered

data can be incrementally supplied Time-efficient vs. Space-efficient Parsers

Time efficient but encoding many states Space efficient but with backtracking

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Related Work [Van Engelen, 2001]

The earliest work on schema-specific LL(1) recursive descent parser w/ namespace support and validation

[Van Engelen, 2004] Two-level DFA integrating parsing and validation

[Chiu et al., 2004] Using nondeterministic generalized automata to

merge all aspects of low-level parsing and validation

[Reuter, 2003] Using Cardinality-Constraint Automaton (CCA) to

perform schema-aware validation

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Related Work (Cont’d) [Kostoulas et al., 2006]

An efficient parser generator that translates XML schema into a parser either in C or Java

[Matsa, 2007]Schema-directed interpretive XML parser

using special purpose byte-codes. [Zhang et al., 2006]

A table-driven approach parsing and validating in a single pass

Generator that translates schema in C

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PTDX: Table-Driven XML Parser with Permutation Phrase Table-driven grammar-based parser

Extended LL(1) grammar with permutation phrase support Parsing table is constructed from extended LL(1) permutation

grammar Run-time parser

Generic parsing engine (2-stack PDA) Both time and space efficient

Predictive parsing Integrating parsing and validation into a single pass No buffering Operating on tokens Main stack size growing in depth of XMLdata Auxiliary stack size growing in number of elements of <xs:all>,

<xs:attribute> Non-blocking parser

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Constructing PTDX Tables

XML Schemas Mapping

Rules

Extended LL(1) Permutation Phrase

Grammar

LL(1)Parsing Table

TokenTable

ActionTable

Note: actions are generated from schemas to perform type-checking verification although some validation constraints are incorporated in grammar productions.

Note: actions are generated from schemas to perform type-checking verification although some validation constraints are incorporated in grammar productions.

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Mapping Rules Define translation from schema

components to LL(1) grammar productions Preserve structural constraints Map Free-ordered schema components

(<xs:all>, <xs:attribute>) to permutation grammar

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Mapping Example

<complexType name=“T”> <all> <element name=“a” type=“string” minOccurs=“0”/>

<element name=“b” type=“string”/> <element name=“c” type=“string”></all> </complexType>

T → << A || B || C >>

A → bA CD eA

A → ε

B → bB CD eB

C → bC CD eC

Note: bA and eA representing tokens of starting and closing element “a” Respectively; CD representing token of CDATA

Note: bA and eA representing tokens of starting and closing element “a” Respectively; CD representing token of CDATA

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Permutation Phrase

A permutation phrase is a grammatical phrase that specifies a syntactic construct as any permutation of a set of constituent elements.

E.g., the permutation phrase

<< a || b || c >>

recognizes language {abc, acb, bac, bca, cab, cba}

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Two-stack PDA for Parsing Permutation Phrase

<< a || b || c>>

abc

top

Main stack Aux stack

b c aInput:

bctop

Main stack

a

Aux stack

b c aInput:

actop

Main stack Aux stack

b c aInput:

top

1 2 3

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Two-stack PDA for Parsing Permutation Phrase (Cont’d)

<< a || b || c>>

Main stack Aux stack

4 5 6

ctop

Main stack

a

Aux stack

top

b c aInput:

atop

Main stack Aux stack

b c aInput: b c aInput:

Note: All optional constituent elements are left on auxiliary stackonce all non-empty elements have been parsed. Note: All optional constituent elements are left on auxiliary stackonce all non-empty elements have been parsed.

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PTDX ArchitectureHot-swappableHot-swappable

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Schema-directed Scanner Optimized by schema

E.g., scanning a specific tag name is more efficient than scanning the generic string then doing comparison

Tokenizer Breakes XML message into token stream

Token Defined by element names, attribute names,

enumeration values Classified as starting tags and closing tags Normalized namespace binding

<namespace, tag_name>

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Experiment Settings

Test environment 3.0 GHz, 2GB RAM, Linux 2.6.20-1.2320, GCC 4.1.1 with option

-02 Memory-resident message Randomly arranged free ordered elements

Compared with Validation parsers

gSOAP 2.7 Xerces 2.7.0 pTDX flex based parser

Non-validation parsers Expat 2.0.1 DFA-based parser

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Test Cases

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Performance: comparison of validating and non-validating parsers

Bett

er

perf

orm

ance

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Performance: effect of number of elements in <xs:all> of PTDX parser

Bett

er

perf

orm

ance

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Performance: runtime and compile time memory usage comparison(32 <xs:all> elements)

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Conclusion

Free ordered constraints can be parsed and validated efficiently using a 2-stack PDA

Table-driven permutation phrase grammar parsing technique is time and space optimal

Table-driven approach offers flexible framework for dealing with schema evolvement