An Extension to XML Schema for Structured Data Processing

1
An Extension to XML Schema for Structured Data
Processing

• Presented by Jacky Ma
• Date 10 April 2002

2
Presentation Outline

• The Problems
• Research Objectives
• The Schema Extension MMX
• MMX Query System
• Discussion
• Conclusion

3
The Problems

• Mapping XML data into relational tables
• Not natural to XML structure
• Efficient, but may not be a effective method
• Legacy application-specific structured data
• Similar modeling but proprietary implementation
• Not interoperable, and difficult to maintain
• Lack of modular design and thus difficult to
  combine to form more complex data structure
• Meta-data can facilitate wide range of needs,
  while XML Schema is solely used for physical data
  validation nowadays

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Research Objectives

• To facilitate more effective searching and
  storing of XML contents by making use of
  meta-data (XML Schema)
• Propose a data-oriented model to allow different
  storage mechanism, processing model, and query
  model on XML contents

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Our Approach MMX

• Use meta-data to map XML data into structured
  data objects
• Define the structured data models conceptually
  and link the models to XML document structure
  syntactically
• Meta-data is defined as an extension of XML
  Schema
• The extension is called MMX (Multi Model XML)

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Program Driven vs. Data Driven
Information for processing is hard-coded in
program
Program Driven
MMX!
Data Driven
Processing instruction is hard-coded in data?!
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A Glance of XML Data
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A Glance of The Linked Schema
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Schema Extension

• The extended schema is associated with a
  namespace
• The extended schema goes within a schema element,
  like lttreeelementgt in the example
• lttreeelementgt specify a single structure object
  instance
• Name association for elements and attributes
• Class hierarchies
• lttreeelementgt -gt lttreeinternalgt -gt
  lttreeleafNodegt
• finally to the structure specified in
  lttreeleafNodeValuegt
• Additional properties in ltrootNodeAttrgt,
  ltinternalNodeAttrgt and ltleafNodeAttrgt
• Schema writer has to know the structure model
  specification, while the XML writer only needs to
  know the given schema

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Modeling

• For an instance of MMX data object
• As an encapsulated information object only
  accessible from the root, thus as a single tree
  node
• As a mapping from root node, query method and
  query parameters to the value at leaf nodes
• Leaf nodes may contain any valid XML content, as
  long as defined in the Schema
• I.e. may contain another MMX data object
• A query is modeled as a 3-dimension tuple
• accessing-node, query-method, query-parameters
• Accessing-node is specified by XPath
• Query-method is specified in String Value
• Query-parameters is multi-dimension depends on
  the current model

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Modeling (2)
A
Tree(1) is accessible frompoint A, occasionally,
a query (e.g. A, spatial-search,(3, 5),
assuming Tree(1) will accept spatial-search
with two coordinates) may return point B as
answer, either by XPath of B or the XML subtree
of B. From this point B, user may drill down
the tree by issueanother query on Tree(2).
Tree (1)
B
Tree(2)
XML Elements..
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Query with and without MMX

• From the original XML data, we could not assume
  the semantics of the data
• We can ONLY do XML-based query such as XPath
• We can do the spatial query ONLY IF we can map
  the data into a R-Tree
• After mapping the data into R-Tree
• Spatial Queries
• Give me the point at (2,7)
• Give me the point nearest to (4,4)
• Nearest Neighbor Search
• Give me the point nearest to Franklin

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Processing

• Users might not know the type of the node (and
  not necessary to know). They are interested in
  what they can do
• Users retrieved the list of possible operation by
  issuing a LIST-OPERATION method to the root
  element of a MMX object
• Possible operations may include queries, updates,
  and other model-specific operations

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MMX Query System

• To show that the schema, modeling, and processing
  of MMX extension is workable
• To illustrate how it assists in querying XML data
• To facilitate as the platform for testing the
  implementation of arbitrary structured models
• Implement with JDK1.4

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System Design
Clients
XML
DOM
MMXDocument
Node Data
Schema
MMX Element
ParseSchema
FetchClasses
AbstractMMX Element
The Abstract Class defines common interface that
have to be implement in each MMX Element such as
LIST-OPERATION, QUERY, BUILD, etc.
Extends class
(Partly)Defines

VP-Tree
X-Tree
R-Tree
R-TreeSchema
Maps
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Discussions - Pros

• Compatible with the relational approach, and
  supersedes that.
• Modular design promotes reusability and
  maintainability
• XML flatten the legacy structured data to make
  them text-editable, easy to transport and process
  by different systems

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Discussion - Cons

• There is no generic syntax to precisely describe
  all kinds of structures models
• The size of XML file is often larger than legacy
  data file
• Each structure model needs additional
  implementation effort
• Schema specification become longer and longer
  quickly as number of supported model increases

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Conclusion

• Propose a representation to encapsulate data
  structures
• Describe XML data with the Schema conceptually as
  well as syntactically
• Map legacy structure models into Schema, and map
  XML data to the structure models by the Schema
• Structured data repository with increased
  interoperability, reusability, and
  transportability

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QA