Interoperability and XML

1
Interoperability and XML

• David Nelson/Sue Patience
• CAT
• May 2005

2
Objectives

• To investigate issues surrounding
  interoperability
• To gain a basic understanding of XML and its
  developments related to database systems
• To gain a basic understanding of the use of XML
  towards achieving interoperability

3
Interoperability

• IEEE (1990) Definition
• the ability of two or more systems or components
  to exchange information and to use the
  information that has been exchanged
• IEEE Standard Computer Dictionary A Compilation
  of IEEE Standard Computer Glossaries
• Current simple solutions
• mediation
• transformation

4
Features

• Exchange of messages and requests
• Use of each others functionality
• Client-server abilities
• Distribution
• Operate multiple systems as single unit
• Communication despite incompatibilities
• Extensibility and evolution

5
The Problems and Difficulties

• Different data models
• There can be major semantic differences even
  within the same data model
• Properties may be called by different names
• Different data types may be used
• What about recreating local defined functions?

6
The Problems and Difficulties

• All this implies we know where they are and we
  have a physical means of getting to them
• Databases are by their nature protectors of
  data, they do not share easily
• Many (particularly legacy systems) do not have
  any form of web interface
• Most databases are security protected
• Databases do not advertise their services to the
  web

7
Some Simple Problems 1

• Differing schema
• author char(50) author_surname char(50)
• author_inits char(10)
• title varchar(300) title varchar(200)
• keyword set(char(30)) keywd array(8) (char(30))
• - both are valid schema in SQL2003
• also A.N.Other, A N Other, Other N A, ...

8
Some Simple Problems 2

• Homogeneous Models
• the same information may be held as attribute
  name, relation name or a value in different
  databases
• e.g. library fines
• as a dedicated relation Fine(amount,
  borrowed_id)
• as an attribute Loan(id, isbn, date_out, fine)
• or as a value Charge(1.25, fine)

9
Complex Problems

• Heterogeneous models
• Need to relate model constructions to one
  another, for example
• relate classes in object-oriented to user-defined
  types in object-relational
• Or even more problematic, to tables in a
  relational database
• All problems are magnified at this level!

10
Extensible Markup Language (XML)

• A simplified version of SGML, designed
  specifically for Web documents
• a meta-language to create customised tags which
  provide functionality not available in HTML
• links can point to multiple documents
• links can be bi-directional
• links to relative objects
• broken into
• stylesheet (XSL standard)
• document type definition (DTD) for well-formed
  documents
• document data

11
Sample XML Database

• lt?xml version 1.0 encoding UTF-8
  standaloneyes?gt
• lt?xmlstylesheet type text/xsl
  hrefstaff_list.xsl?gt
• lt!DOCTYPE STAFFLIST SYSTEM staff_list.dtdgt
• ltSTAFFLISTgt
• ltSTAFF branchNo B005gt
• ltSTAFFNOgtSL21lt/STAFFNOgt
• ltNAMEgt
• ltFNAMEgtJohnlt/FNAMEgtltLNAMEgtWhitelt/LNAMEgt
• lt/NAMEgt
• ltPOSITIONgtManagerlt/POSITIONgt
• lt/STAFFgt
• ltSTAFF branchNoB003gt
• lt/STAFFLISTgt

12
Sample DTD

• lt!ELEMENT STAFFLIST (STAFF)gt
• lt!ELEMENT STAFF (NAME, POSITION, DOB?, SALARY)gt
• lt!ELEMENT NAME (FNAME, LNAME)gt
• lt!ELEMENT FNAME (PCDATA)gt
• lt!ELEMENT LNAME (PCDATA)gt
• lt!ELEMENT POSITION (PCDATA)gt
• lt!ATTLIST STAFF branchNo CDATA IMPLIEDgt

13
Sample StyleSheet

• lt?xml version 1.0?gt
• ltxslstylesheet xmlnsxsl http//www.w3.org/TR/
  WD-xslgt
• ltxsltemplate match /gt
• lthtmlgtltbodygt
• ltcentergtlth2gtDreamHome Estate agentslt/h2gtlt/center
  gt
• lttable border 1 bgcolor ffffffgt
• lttrgt
• ltthgtstaffNolt/thgt
• --- repeat for other column headings
• ltxslfor-each selectSTAFFLIST/STAFFgt
• lttrgtltxslvalue-of-selectSTAFFNO/gtlt/tdgt
• lttrgtltxslvalue-of-selectNAME/FNAME/gtlt/tdgtlt/t
  rgt
• lt/xslfor-eachgtlt/tablegtlt/bodygtlt/htmlgt
• lt/xsl-stylesheetgt

14
Benefits of XML

• Simplicity
• Open standard and platform/vendor-independent
• Extensibility
• Reuse
• Separation of content and presentation
• Improved load balancing
• Due to client side processing

15
Benefits of XML

• Support for integration of data from multiple
  sources
• Ability to describe data from a wide variety of
  applications
• More advanced search engines
• XQuery
• New opportunities

16
XML Schema

• ltxsdgroup-name STAFFTYPE
• ltxsdelementnameSTAFFgt
• ltxsdcomplexTypegt
• ltxsdsequencegt
• ltxsdelement name STAFFNO
  typeSTAFFNOTYPE/gt
• ltxsdelement name NAMEgt
• ltxsdcomplexTypegt
• ltxsdsequencegt
• ltxsdelement name FNAMEgt
  type xsdstring/gt
• ltxsdelement name LNAMEgt
  type xsdstring/gt
• lt/xsdsequencegt
• lt/xsdcomplexTypegt
• ...

17
XQuery

• A query language for XML
• e.g. List the staff at branch B005 with a salary
  greater than 15000
• FOR S IN document(staff_list.xml)//STAFF
• WHERE S/SALARY gt 15000 AND
• S/_at_branchNo B005
• RETURN S/STAFFNO

18
Storing XML in a Relational Database

• Three approaches
• Fine Grained
• Course Grained
• Medium Grained

19
Fine Grained Approach

• Good for queries which need to inspect/manipulate
  specific elements in the XML document
• Not good for queries which manipulate (e.g.
  retrieve/store) the entire document

Child
Element ( parent)
Document
CharData
Attribute
20
Course Grained Approach

• One table
• Best for queries which manipulate whole document
• e.g. retrieve/store a document
• Worst for queries which manipulate elements
• e.g. retrieve children of a tag

21
Medium Grained Approach

• A compromise between fine and course grained
• Slice document tree up into sections
• Store sub-sections using a course grained
  approach
• Good for both types of queries

22
XML RDF

• Resource Description Framework
• XML Schema defines a grammar
• therefore we have all the problems shown
  previously (e.g. names)
• RDF provides a way to encode domain models
• an infrastructure that enables the encoding,
  exchange and reuse of structured meta-data (W3C)
• Defines semantics, syntax and structure
• this is what we need for interoperable systems

23
RDF Data Model

• RDF Data Model consists of three objects
• Resource
• anything that can have a URL
• Property
• a specific attribute which is used to describe a
  resource
• Statement
• a combination of a resource, a property and a
  value
• e.g. The Author of http//www.dreamhome.co.uk/
  staff_list.xml is John White

24
Summary

• XML is being increasingly used in data models,
  data transmission and data integration
• Interoperability is the key issue and a major
  research area in database systems
• XML and RDF have the potential as a stepping
  stone to achieving this

25
Further Reading

• Connolly and Begg
• chapter 29 (sections 29.1, 29.2 and 29.3)
  discusses XML and its related technologies
• Graves
• Designing XML Databases, Prentice Hall.
• XML Tutorial
• www.w3cschools.com/xml
• RDF introduction (Idiots Guide!)
• http//archive.dstc.edu.au/RDU/reports/RDF-Idiot/