Tamino a DBMS Designed for XML

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Tamino a DBMS Designed for XML

• Dr. Harald Schoning
• Presenter Wenhui Li
• University of Ottawa
• Instructed by
• Dr. Mengchi Liu
• Carleton University

2
Abstract

• Who?- Software AG
• What?- XML database management system
• When?
• 1999 the first time unveiled
• 2004 June Tamino XML Server 4.2
• Why?
• management and transfer of structured and
  unstructured data
• completely designed for XML

3
Industry Background

• XML is becoming prevailing for data processing in
  the internet.
• Early goals of Tamino
• Easy data exchanging
• Evolution trend
• Storing, managing, publishing and exchanging XML
  documents
• Business modeling

4
Industry Background contXML support in
databases

• Oracle XML Developers Kit
• SQL Server 2000
• DB2 XML Extender

5
Limitations of XML support via traditional RDBMS
or ORDB

• XML is not well-structured like RDB,ORDB or OODB
• Storing and querying XML is possible but not
  feasible in these DB systems

6
Two Modeling approaches

• Data-centric documents
• Regular structure
• Order does not matter
• No mixed content
• Document-centric documents
• less regular structure
• significance of the order
• mixed content

7
Why dont use relational DB

• XML documents can have schematic information
  (DTD), but they are not required to.
• classical database handling objects of a
  predefined type, cannot be applied in XML

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Why doesnt use XML itself?

• XML is just a markup language, it does not
  contain processing facilities on its own
• querying a set of XML documents is outside the
  scope of the XML recommendation
• Therefore, comes the Tamino!

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What does Tamino do?

• Whats Tamino (the 1st slide)
• Store XML documents, HTML files and GIF images,
  etc.
• Retrieve them in a set-oriented manner, with
  sophisticated query facilities

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Taminos architecture
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The schema of XML documents

• XML support schematic information, but it differs
  from the classical databases
• DTD have a couple of deficiencies (e.g. data
  type)
• W3C working group is developing an XML schema
  description language
• However, DTD is the only standard schema at
  present

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XML schema vs. RDB and OODB schema

• In RDB or OODB, the schema is created before the
  instances can be stored
• Instances must conform to the declared schema
• In XML database, each instance declares a schema
  on its own.
• for XML documents, grouping of objects of
  homogeneous structure into (pre-defined) tables
  or classes doesnt work

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Query and Index of XML schema

• Queries operate on sets
• Indexes are defined on the basis of a common
  schema
• For the purpose of querying, arbitrary objects
  could be grouped to sets
• Index definition also requires at least a common
  subset in the structure

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Schema handling in Tamino

• Grouping documents by open content model
  user-directed document grouping
• Documents grouped into collections
• Within a collection, declare several document
  types
• For each document type define a common schema
  (open content model)
• For each document, Tamino assigns one of the
  document type

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Type Assignment

• Assignment is based on the root element type
• Document must match the schema of the document
  type assigned, but might have additional
  elements/attributes
• In a document type, documents might differ
  considerably
• If no appropriate document type, document is
  stored without any schema checking

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Tamino schema example
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Document accepted by Tamino

• ltCity Inhabitants138000gt
• ltNamegtDarmstartlt/Namegt
• ltAdditiongtThe city of art nouveaudlt/Addtiongt
• ltMonument Height39mgt
• ltNamegtLanger Ludwiglt/Namegt
• ltLocationgt
• ltNamegtLuisenplatzltNamegt
• ltMapIndexgtM5lt/MapIndexgt
• lt/Locationgt
• lt/Monumentgt
• lt/Citygt

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Is an element/attribute should be modeled?

• an index will be defined on this
  element/attribute
• the element/attribute is to be mapped to an
  external data source or to a server extension
• dedicated access rights will be defined on the
  element/attribute
• the presence / multiplicity of the element is to
  be enforced
• one of the above conditions hold for a child of
  the element

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Indexing of Tamino

• value-based indexes
• well known from traditional database systems
• used to accelerate the search
• exactly address the data object
• names need not be unique within a DTD

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Example of value-based index

• value-based indexes
• data-centric view
• lt!ELEMENT City (Name, Inhabitants, Monument)gt
• lt!ELEMENT Monument (Name, Description)gt
• lt!ELEMENT Inhabitants (PCDATA)gt
• lt!ELEMENT Name (PCDATA)gt
• lt!ELEMENT Description (PCDATA)gt

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Indexing of Tamino (cont)

• text indexing
• document-centric view
• limit the scope to a specific part of the
  document
• the scope might span element content

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Example of text index

• text indexing
• document-centric view
• ltstatementgt
• ltauthorgt
• ltfirstnamegtHaraldgtlt/firstnamegt
• ltlastnamegtSchoninglt/lastnamegt
• lt/authorgt
• lttextgt
• XltitalicgtMlt/italicgtL and XltitalicgtSlt/italicgtL
  
• are ltstressedgtverylt/stressedgt important
• lt/textgt
• lt/speechgt

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Indexing of Tamino (cont)

• structural index
• If multiplicity permits the omission of elements
• or if no DTD is known
• Example
• in a database of all European cities
• search all those cities which have an element
  called beach

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Querying XML documents

• Currently, there is no standardized query
  language
• XPath allows positioning within a single document
• XPath fits well the needs of retrieval in
  data-centric environments
• document-centric environments need a more
  content-based retrieval facility
• Tamino also supports full text search

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Expectation for XML processor

• W3CXML recommendation specifies the handling of
  entities, comments and processing instructions.
• User Tamino, leave comments intact, no
  processing instruction evaluated, leave entity
  references unresolved.
• User the output of a Tamino query should match
  the specification of an XML processor.

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Why dont leave entities unresolved?

• In case result is a set of (parts of) matching
  documents
• This result DTD must include all different entity
  declarations of the original document
• Definition of the entity might differ from
  document to document
• So, for the same entity name, entities are
  renamed, and the entity references are changed
  accordingly.

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problems of external entities

• These entities can change without the database
  system knowing about this
• Thus, the values of external entities must not be
  included in indexes
• Example
• lt!ENTITY mysubject SYSTEM
• http//www.softwareag.com/hottopic.xmlgt
• ...
• lttickergtTodays hot topic mysubjectlt/tickergt
• Checking the current contents of the external
  entity lead to unacceptable response times.

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Relational Databases and XML

• major (object-) relation database systems include
  some forms of XML support
• The simplest form is to generate XML documents
  for existing relational data.
• But, real database handling of XML requires that
  XML data can be stored and retrieved
• Two approaches

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XML support approach(1)

• Map the XML document is to relational tables and
  their columns
• Markup is ignored on storage, and reconstructed
  on retrieval
• advantage of this approach
• the contents of an XML document can be handled
  with traditional SQL

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XML support approach(1) cont

• Shortcomings
• The sequence information lost
• ltOrder CustomerId567 Date12- 12-2000gt
• ltItem ProductID 17 Quantity2/gt
• ltItem ProductIDl6 Quantity9/gt
• ltItem ProductID 19 Quantity8/gt
• lt/Ordergt
• The retrieval of the order
• ltOrder CustomerId567 Date12-12-2000gt
• ltItem ProductID 16 Quantity9/gt
• ltItem ProductID 17 Quantity2/gt
• ltItem ProductID 19 Quantity8/gt
• lt/Ordergt

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XML support approach(1) cont

• Data-centric documents sequence might not matter,
  it does for document-centric
• this approach loses all comments and processing
  instructions
• mixed content cannot be stored easily in this
  model

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XML support approach(2)

• Leaves the XML document intact and stores it in a
  large text field (BLOB)
• Or even outside the database
• Text search is possible
• Can limit a certain text-based condition

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XML support approach(2) cont

• Limitations
• no structure-aware combinations are possible
• Value-based search is not supported on these text
  fields
• IBM solution side tables
• But, direct manipulation of side tables destroys
  the consistency of the database
• Security can be defined on document level only,
  but not on elements or attributes

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Summary

• Tamino was designed with particular attention to
  the XML
• Schema handling for XML is different from
  relational databases does
• In Schema handling, external entities cause
  conceptual problems
• value-based indexes are useful for XML, as well
  as text index and structural index
• Comments and processing instructions should be
  preserved when documents are stored
• The result of a query against an XML database
  should be XML

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QA

• Thanks!