Active XML

1
Active XML
INFO613 XML and Database

• Xiaohua (Davis) Zhou
• College of Information Science Technology
  Drexel University

2
Agenda

• What is Active XML (AXML)
• Why Active XML
• AXML Language System
• Research Issues
• Security issue
• Semantic issue
• Other open questions

3
Sample of AXML

• All of the follow three XML chunks describes the
  present temperature of Denver, the capital of
  Colorado.

4
What is AXML?

• AXML is intentional data
• AXML is dynamic data
• Like dynamic web page, ASP, PHP and JSP
• XML Web Service
• XML document with embedded web service call
• XML document where some particular elements (i.e.
  sc) are interpreted as web service call.

5
Why AXML?

• Users have the freedom to get data when needed.
• More convenient to deal with frequently updated
  data such as weather and quote of stock.
• Flexible for data integration
• Always get first-hand data

6
Contribution of AXML

• AXML Language
• Syntax for web service call
• Merge results of web service call
• AXML System

7
AXML Peer as A Client

• When to activate a web service call?
• Explicit pull
• Based on time frequency
• ltsc frequencydailygtlt/scgt
• Implicit pull
• Data is requested
• Push
• The server decides to push information to client.
• How long the returned date remain valid?
• Based on valid attribute
• ltsc valid1 day modelazygtlt/scgt

8
AXML Peer as A Client (Cont.)

• Where to find its arguments?
• The argument of service call is specified by
  children of sc node.
• What to do with the result?
• The result of a service call is inserted at the
  place of the call (as the sibling of the sc node)

9
AXML Peer as A Server

• Pull query and update service
• Push continuous service
• The client subscribes to a particular push
  service by issuing service call, then the server
  synchronously send a stream of messages as an
  answer.

10
AXML Architecture

• The document store, which provides persistent
  storage for AXML documents,
• The evaluator, whose role is to trigger the
  services calls embedded inside AXML documents and
  to update the latter accordingly.
• The XQuery processor deals with the service
  requests, by evaluating the corresponding
  queries.

11
AXML Implementation

• The X-OQL query processor,
• Apache Tomcat 4.0 Servlet engine,
• Apache Axis toolkit 1.0 for web services,
• The JSTL 1.0 standard tag library

12
Security Issue

• Potential Security Harm
• A call may return AXML which contains service
  calls. This is potentially a very serious
  security hole, that allows for Trojan horse style
  attack.
• Trust mechanism

13
Semantic Issue

• Termination
• Suppose that a service f calls some service g,
  and that similarly g calls f.
• Finiteness
• Confluence
• Suppose that is a single hamburger to distribute
  and that two clients are trying to call the same
  method that grab the hamburger. Then the first
  call succeeds but the second fails.
• Consistency
• The returned XML chunks may not conform to the
  DTD (or XML schema) of the whole document.

14
Other Open Issues

• The construction of a warehouse from Web
  resources based on AXML
• Distribution and replication of fragments of AXML
  documents
• Development of a visual AXML editor
• Building AXML on mass storage systems.
• Optimization of query.

15
References

• http//activexml.net/
• Active XML Primer ftp//ftp.inria.fr/INRIA/Project
  s/gemo/gemo/GemoReport-307.pdf