XEM:%20Managing%20the%20Evolution%20of%20XML%20Documents

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XEM Managing the Evolution of XML Documents

• Author Hong Su, Diane Kramer. Li Chen, Kajal
  Claypool and Elke A. Rundensteiner
• Presented by Li Shuhong
• Fall 2001 CS401
• Nov. 20, 2001

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Motivation

• XML has become increasingly popular as the data
  exchange format over the Web. DTDs assume a
  similar role as types in programming languages
  and schemata in database systems
• Many systems utilize the given DTD to construct a
  fixed relational schema. This schema can serve as
  structure based on which to populate the XML
  documents that conform to this DTD
• Change is a fundamental aspect of persistent
  information and data-centric system. Most of the
  current XML management systems dont provide
  enough support for these changes.

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Motivating Example of XML Changes

• lt!ELEMENT article (title, author,
  related-work?)gt
• lt!ELEMENT title (PCDATA)
• lt!ELEMENT author (name)gt
• lt!ATTLIST author id ID REQUIREDgt
• lt!ELEMENT name (firstrname, lastname)gt
• lt!ELEMENT firstname (PCDATA)
• lt!ELEMENT lastname (PCDATA)
• lt!ELEMENT related-work (monogragh)gt
• lt!ELEMENT monograph (title, editor)gt
• lt!ELEMENT editor, EMPTYgt
• lt!ATTLIST editor name CDATA IMPLIEDgt
• ltarticlegt
• lttitlegtXML Evolution Managerlt/titlegt
• ltauthor id dkgt
• ltnamegt
• ltfirstnamegtDianelt/firstnamegt
• ltlastnamegtDianelt/lastnamegt
• lt/namegt

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Example

• Removal of lteditor name Won Kimgt
• XML change support system would need to verify
  that
• 1. A new valid DTD.
• 2. Change all old XML documents to conform to the
  changed DTD
• Result of the example this change leads to a DTD
  change, requiring no changes of the underlying
  XML data.
• Problems with XML Management System
• To updates the code, the users must be aware of
  underlying storage system and the mapping
  mechanism between XML, DTD, and their underlying
  storage model in order to prevent the errors of
  mismatch of desired XML transformation and the
  actual system change.

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XML data Model The DTD Data Model

• XML is composed of nested tagged elements,
  attributes, and sub-elements. It may have an
  associated schema, and DTD.
• Document Type Definition(DTD) allows for
  properties or constraints to be defined on
  elements and attributes.
• A DTD can be modeled as graph, G (N, p, l),
  where N is the set of nodes, p is the parent
  function representing the edges in the graph, and
  l is the labeling function representing a tuple
  of nodes properties.

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Graph Representation of Article.dtd
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Taxonomy and Semantics of XML Change Primitives

• Present the taxonomy of XML change primitives and
  define their semantics. Those primitives fall
  into two categories
• 1. pertaining to the DTD.
• 2. pertain to XML data.
• The primitives have the following
  characteristics
• Complete
• Minimal each primitive is atomic
• Sound consistency, integraty
• Example
• changeQuant(monograph, 1,2,?)
• destroyDataEl(article/related-work/monograph1/e
  ditor)

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Advantages

• Identify the lack of generic support for change
  in XML management systems.
• Provide a system to specify changes both at the
  DTD and XML data level
• Introduce the notion of constraint checking to
  ensure structural consistency.
• Express desired transformation independent of the
  underlying storage system.
• Describe a working XML Evolution Management
  prototype system MARROW
• Disadvantages
• This systems only allows simple pre-defined
  schema evolution operation