Peer-to-Peer Data Integration with Active XML Tova Milo Tel-Aviv - - PowerPoint PPT Presentation

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Tova Milo – Tel Aviv University

Peer-to-Peer Data Integration with Active XML

Tova Milo

Tel-Aviv University

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Tova Milo – Tel Aviv University

Active XML - Outline

Introduction Active XML

• Active XML documents
• Active XML services

Novel issues

• Exchanging Active XML data
• Querying Active XML data
• Distribution and replication
• Security and Access control

Active XML Peers

• The peer as a client
• The peer as a server
• Theoretical foundations

Applications Conclusion

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Introduction

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Distributed data management in P2P Information is everywhere

services XML XML services XML XML XML XML services XML services XML Web Web service Web service Data warehouses Databases Web sites PC, PDA, cell phones, home appliances, cars…

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The golden triangle

• f distributed data management

XML

• a standard for data representation & exchange

Query languages

• XPath, XQuery

Web services

• standards for distributed computing
• Activation of methods on remote servers

XQuery XPath XML Web services

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What is Active XML (AXML)?

AXML is a declarative language for distributed information management and an infrastructure to support this language, in a peer-to-peer framework.

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Active XML

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Active XML documents

XML documents with embedded calls to Web services

Intensional

• Some of the data is given explicitly
• Some is given intensionally

(i.e. the means to acquire data when needed are given)

Dynamic

• If the external sources change, the same document will provide

different information

• Reaction to world changes

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Not a new idea in databases, nor on the Web

Mixing calls to data is an old idea

• Procedural attributes in relational systems
• Basis of Object-oriented Databases

In HTML world

• Sun’s JSP, PHP+MySQL

Calls to Web services inside XML documents

• Macromedia FLEX, Apache Jelly, Microsoft XAML

What is new is the exploitation of the idea…

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A sample AXML document

<?xml version=“1.0” ?> <newspaper> <title>Le Monde</title> <date>06/10/2003</date> <call svc=“Yahoo.GetTemp”> <city>Paris</city> </call> <call svc=“TimeOut.GetEvents”> exhibits </call> </newspaper>

GetTemp city “Paris” newspaper title date “06/10/2003” “Le Monde” GetEvents “Exhibits”

AXML documents may contain calls:

• to any existing Web services

(e-bay.net, google.com…)

• to any AXML Web services

(to be defined)

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Materialization

We will see later that:

• Replacing the call by its result is not the only option
• Calls are not necessarily RPC-style synchronous invocations

<?xml version=“1.0” ?> <newspaper> <title>Le Monde</title> <date>06/10/2003</date> <call svc=“Yahoo.GetTemp”> <city>Paris</city> </call> <call svc=“TimeOut.GetEvents”> exhibits </call> </newspaper>

GetTemp city “Paris” newspaper title date “06/10/2003” “Le Monde” GetEvents “Exhibits”

• temp

“16° C”

SOAP call

<temp>16°C</temp>

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AXML Web services

Parameters: AXML data Result: AXML data

Distribute computations: by sending as parameters data containing service calls, one can delegate some work to other peers Partial computations: by returning data containing service calls, one can give to the receiver the control

• f these calls

Great flexibility

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Calling an AXML service

<?xml version=“1.0” ?> <newspaper> <title>Le Monde</title> <date>06/10/2003</date> <call svc=“TimeOut.GetEvents”> exhibits </call> </newspaper>

newspaper title date “06/10/2003” “Le Monde” GetEvents “Exhibits”

<temp>16°C</temp>

exhibits GetExhibits “Paris” City

• temp

“16° C”

SOAP call (still…)

Materialization is a recursive process Termination is an issue

<exhibits> <call svc=“Yahoo.GetExhibits”> <city>Paris</city> </call> </exhibits>

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Novel issues

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Active XML - Outline

Introduction Active XML

• Active XML documents
• Active XML services

Novel issues

• Exchanging Active XML data (SIGMOD’03, PODS’05)
• Querying Active XML data
• Distribution and replication
• Security and Access control

Active XML Peers

• The peer as a client
• The peer as a server
• Theoretical foundations

Applications Conclusion

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To call or not to call ?

GetEvents “Exhibits” newspaper title date “Le Monde” “06/10/2003” GetTemp city “Paris” temp “16° C”

• Materialization can be performed

by the sender, before sending a document

• r by the receiver, after receiving it

GetEvents “Exhibits” newspaper title date “Le Monde” “06/10/2003” GetTemp city “Paris” temp “16° C”

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Why control the materialization of calls?

For added functionality, e.g.

• Intensional data allows to get up-to-date information

For security reasons or capabilities, e.g.

• I don’t trust this Web service/domain
• I don’t have the right credentials to invoke it
• It costs money
• Maybe the receiver doesn’t know Active XML!

For performance reasons, e.g.

• A proxy can invoke all the services on behalf of a PDA

… and many more reasons you can think of!

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We extend XML Schema, with intensional types: XMLSchemaint

How to control it? Using types

Casting algorithms use signatures of services: WSDLint

... ...

r

... ... ... ... ...

g f q

...

Capabilities ACL Cost ... Sender

data exchange Schema

f q g

Capabilities ACL Cost ... Receiver

g g g g g g q q q f f r r

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Rewritings

The Goal:

Given

• an AXML document d
• a schema s

Can we rewrite d so that it matches s?

Safe rewriting: one that for sure leads to s (we know without making any call) Possible rewriting: one that possibly leads to s (depending on the answers of the services)

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Results

The general problem is undecidable [MSS04] Restrictions on the considered rewritings

• Left-to-right: No “going back and forth”
• K-depth: bound on the nesting of function calls

(Search space still infinite but finitely representable)

Under these restrictions

• We have algorithms to find safe/possible rewritings
• They are PTIME (for deterministic schemas)
• We can also do it between schemas

Implementation

• first demo at VLDB 2003 (customizable news syndication)

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Active XML - Outline

Introduction Active XML

• Active XML documents
• Active XML services

Novel issues

• Exchanging Active XML data
• Querying Active XML data (SIGMOD’04, PODS’05)
• Distribution and replication
• Security and Access control

Active XML Peers

• The peer as a client
• The peer as a server
• Theoretical foundations

Applications Conclusion

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Querying AXML Data

Given a (tree pattern) query:

/newspaper[temp > 18°C]/exhibits//exhibit[location=“Le Louvre”]

Materialize the document? Call only the services that may contribute data to the query answer.

The problem: Lazy evaluation of service calls To call or not to call, this time when evaluating a query

GetTemp city “Paris” newspaper title getDate “Le Monde” GetEvents “Exhibits” exhibits GetExhibits “Paris” City temp “19° C”

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Lazy evaluation

Difficulties:

• Calls can be found everywhere in the document
• May appear dynamically (as a result of previous calls)
• May become (ir)relevant due to previous invocations
• Need to take signatures of calls into consideration

Possible approach: modify the query processor

• Trigger the calls found on the way
• Not so great:

– Computation is blocked – Optimization opportunities are lost

Our solution:

• Drives queries that find the relevant calls (recursively)
• Use service signatures to prune irrelevant calls
• Parallel call invocations
• Pushing queries to capable external sources

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Tova Milo – Tel Aviv University

Active XML - Outline

Introduction Active XML

• Active XML documents
• Active XML services

Novel issues

• Exchanging Active XML data
• Querying Active XML data
• Distribution and replication
• Security and Access control

Active XML Peers

• The peer as a client
• The peer as a server
• Theoretical foundations

Applications Conclusion

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Active XML peers

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Distributed data management in P2P

services XML XML services XML XML XML XML services XML services XML Web Web service Web service

AXML AXML AXML

AXML AXML AXML AXML

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What is an AXML peer ?

Repository: manages persistent AXML data Client: uses (AXML) Web services to dynamically enrich data Server: easy (declarative) definition of AXML services

AXML peer soap

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Global architecture

• AXML

XML AXML AXML

AXML store

service descriptions

AXML engine Query engine

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Tova Milo – Tel Aviv University

Active XML - Outline

Introduction Active XML

• Active XML documents
• Active XML services

New issues

• Exchanging Active XML data
• Querying Active XML data
• Distribution and replication
• Security and Access control

Active XML Peers

• The peer as a client
• The peer as a server
• Theoretical foundations

Applications

• P2P auctions
• News syndication
• Other applications

Conclusion

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Managing persistent AXML data

“Our newspaper should have its temperature information refreshed daily. New exhibits should be fetched every week and archived for 6 months” Service call results enrich the document (calls can be kept for possible future reuse) Main issues:

• When to activate a service call? (pull/push, implicit/explicit)
• What to do with its result? (add/replace/merge)

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Example: AXML document with control attributes

<?xml version=“1.0” ?> <newspaper> <title>Le Monde</title> <date>06/10/2003</date> <call svc=“Yahoo.GetTemp” mode=“lazy” valid=“1 day” merge=“replace” > <city>Paris</city> </call> <call svc=“TimeOut.GetEvents” mode=“every Monday morning” valid=“6 months” merge=“append”> exhibits </call> </newspaper>

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Providing declarative AXML services

Services can be defined by queries or updates over the AXML documents of the repository (XQuery, XPath, Xupdate) Users can subscribe to services Services can be composed (BPEL4WS)

Which (lazy) service calls may contribute to the answer?

let service GetExhibitsByLocation($loc) be for $a in document(“newspaper.xml")/newspaper/exhibits, $b in $a//exhibit where $b@name=$loc return <exhibits> {$b} </exhibits>

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Active XML - Outline

Introduction Active XML

• Active XML documents
• Active XML services

New issues

• Exchanging Active XML data
• Querying Active XML data
• Distribution and replication
• Security and Access control

Active XML Peers

• The peer as a client
• The peer as a server
• Theoretical foundations (PODS’04, PODS’05)

Applications Conclusion

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Applications

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Demos

Peer-to-peer auctions (VLDB 2002 demo)

• Discovery of new peers/auctions through intensional answers

RSS News syndication (VLDB 2003 demo)

• Customization of services through schemas + news subscriptions

Decentralized management of patient data (VLDB 2004 demo)

• Use AXML to coordinate the integration of data

and privacy enforcement services in a uniform way

Querying Business Processes (VLDB 2005 demo)

• Use AXML to model and query BPEL specifications

Others…

A powerful framework for the fast development

• f distributed, data-centric applications.

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Other applications

Dynamic warehouse on food risk management (E.dot)

• Use AXML as the platform for the warehouse definition,

construction and maintenance

Network configuration (SWAN)

• Consider using AXML exchange of information to

configure hardware/software components

Software distribution (EDOS)

• Consider using AXML to customize distributions and

keep your view of the software fresh

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Conclusion

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AXML documents and services

A simple paradigm… …that allows for new, powerful features

• Intensional parameters and results:

AXML documents can be exchanged

• Support for continuous services (streams of answers)
• Control over the exchange of AXML data
• Lazy query evaluation

AXML implementation goes Open Source (ObjectWeb consortium)

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Thanks: Serge Abiteboul, Omar Benjelloun, Ioana Manolescu, Bernd Amann, Jerome Baumgarten, Bogdan Cautis, and many others…