XML and Information Processing

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XML and Information Processing
T.B. RajashekarNational Centre for Science
InformationIndian Institute of ScienceBangalore
560 012(raja_at_ncsi.iisc.ernet.in)
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XML and Information Processing

• Objective of the presentation
• Current web information architecture and HTML
  limitations
• Solution XML (Extensible Markup Language)
• SGML, XML and HTML
• XML components and examples
• XML DTD
• XML applications and vocabularies
• XML and bibliographic information
• Related specifications and standards
• XML resources

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Objective of the Presentation

• To explain a few key concepts related to XML
• To indicate relevance of XML for information
  processing
• To point to related resources

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Current Web Information Architecture
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Limitations of HTML

• Lets look at two typical HTML examples portion
  of a full text paper and a journal TOC (springer
  toc, libaut.htm)
• Mixes data with presentation
• HTML carries only the layout of the document
  not its semantic structure identification and
  extraction of structural elements is very
  difficult poor quality searches
• Has restricted set of tags mostly to do with
  presentation cannot be extended by authors
• Data exchange between applications/ services is
  not possible
• Weak support for validation (now overcome with
  XHTML)

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XML Extensible Markup Language

• XML is specifically designed for the web and as a
  data interchange format
• XML is a simplified subset of Standard
  Generalized Markup Language (SGML)
• Overcomes limitations of HTML with several
  additional advantages
• Formally ratified as a W3C standard in February
  1998
• Specification provides a set of grammar and
  syntax rules for semantically describing the
  structure of data
• Mark the structure of an object (document,
  database entry, etc.) and use this for sharing
  and processing.

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XML Extensible Markup Language

• ASCII of the Web OS independent create once
  and use in different ways
• Quality searching
• Can search for field-based content, not just any
  content
• computer (name/model) price lt 700
• Enables data interchange and sharing between
  applications
• Limitation of XML Does not convey meaning of
  structural elements applications have to
  achieve this also through common XML
  vocabularies

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XML Design Goals

• XML shall be usable over the Internet
• XML shall support a variety of applications
• XML shall be compatible with SGML
• It shall be easy to write programs that process
  XML documents
• Optional features in XML shall be kept to the
  absolute minimum, ideally zero (compatibility)
• XML documents should be human-legible and
  reasonably clear
• Design of XML should be prepared quickly
• Design of XML shall be formal and concise
• XML documents shall be easy to create

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SGML, HTML and XML

• XML is a compromise between the non-extensible,
  limited capabilities of HTML and the full power
  and complexity of SGML
• Claimed to be better than SGML
• 80 of capabilities, 20 of complexity
• Small enough to be supported by browser vendors
• Explicitly includes hyper linking
• Supports style sheets
• Better than HTML
• Extensible (can create your own tags)
• Tags identify content e.g. item and its price

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XML Document Structure
Three Components

• Prolog
• XML Declaration
• Document Type Declaration (optional)
• Processing instructions and comments

• Document Body
• One or more elements, in the form of a
  hierarchical tree, some of which may contain data
• Processing instructions and comments

• Epilog (optional)
• Processing instructions and comments

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XML Document Structure

• All XML documents start with the XML declaration
  lt?xml version"1.0"?gt
• DTD (Document Type Definition) (part of document
  type declaration in prolog), provides the
  vocabulary for the XML documents, and defines
  the document hierarchy, elements, tags and
  syntactic rules for the document structure
• DTD can accompany XML documents or reside outside
  the documents
• Lets take an example and see the two
  possibilities, using IE browser (version 5.0 or
  above) (adbook.xml)

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XML Document With External DTD

• lt?xml version"1.0"?gtlt!DOCTYPE addressbook
  SYSTEM "adbook.dtd"gtltaddressbookgt ltperson
  id"B.WALLACE" gender"male"gt ltnamegt
  ltfamilygtWallacelt/familygt
  ltgivengtBoblt/givengt lt/namegt
  ltemailgtbwallace_at_megacorp.comlt/emailgt
  ltlink manager"C.TUTTLE"/gt lt/persongt
  ltperson id"C.TUTTLE" gender"female"gt
  ltnamegtltfamilygtTuttlelt/familygtltgivengtClairelt/givengt
  lt/namegt ltemailgtctuttle_at_megacorp.comlt/email
  gt ltlink subordinates"B.WALLACE"/gt
  lt/persongtlt/addressbookgt

XML Declaration
Root element
Body
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DTD Stored in adbook.dtd File
lt!-- DTD for a simple address book --gt lt!ELEMENT
addressbook (person)gt lt!ELEMENT person
(name,email,link?)gt lt!ATTLIST person id ID
REQUIREDgt lt!ATTLIST person gender (malefemale)
IMPLIEDgt lt!ELEMENT name (family,given)gt lt!ELEMENT
family (PCDATA)gt lt!ELEMENT given
(PCDATA)gt lt!ELEMENT email (PCDATA)gt lt!ELEMENT
link EMPTYgt lt!ATTLIST link manager IDREF IMPLIED
subordinates IDREFS IMPLIEDgt
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XML Document With Accompanying DTD
lt?xml version"1.0"?gtlt!DOCTYPE addressbook
lt!ELEMENT addressbook (person)gtlt!ELEMENT
person (name,email,link?)gtlt!ATTLIST person id
ID REQUIREDgtlt!ATTLIST person gender
(malefemale) IMPLIEDgtlt!ELEMENT name
(family,given)gtlt!ELEMENT family
(PCDATA)gtlt!ELEMENT given (PCDATA)gtlt!ELEMENT
email (PCDATA)gtlt!ELEMENT link EMPTYgtlt!ATTLIST
link manager IDREF IMPLIED subordinates IDREFS
IMPLIEDgtgt
XML Declaration
DTD
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XML Document With Accompanying DTD
ltaddressbookgt ltperson id"B.WALLACE"
gender"male"gt ltnamegt
ltfamilygtWallacelt/familygt
ltgivengtBoblt/givengt lt/namegt
ltemailgtbwallace_at_megacorp.comlt/emailgt
ltlink manager"C.TUTTLE"/gt lt/persongt
ltperson id"C.TUTTLE" gender"female"gt
ltnamegtltfamilygtTuttlelt/familygtltgivengtClairelt/givengt
lt/namegt ltemailgtctuttle_at_megacorp.comlt/email
gt ltlink subordinates"B.WALLACE"/gt
lt/persongtlt/addressbookgt
Body
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Do We Need a DTD?

• DTD is not mandatory for XML documents
• Lets try this out (use adbook.xml)
• Why do we need DTD then?
• DTD defines the vocabulary for a specific class
  of documents (e.g. reports, theses) - document
  hierarchy, elements, tags and syntactic rules for
  the document structure
• Essential for information exchange between
  applications and services
• Forms the basis for validating the correctness of
  XML documents
• Lets see another example IOP DTD and XML
  files.

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Do We Need a DTD?
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Inside an XML Document (File)

• An XML document file contains one and only one
  document root element
• Root element contains one or more documents
• Document content is marked up using user defined
  elements (tags) and element attributes
• Document content may also contain entity
  references (replacement text, external
  references, etc.).
• Document content may also contain comments and
  processing instructions

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Elements

• XML documents contain data marked up with user
  defined tags
• These tags are referred as elements
• Elements can contain other elements should be
  properly nested
• Consists of a start-tag/end-tag pair, along with
  the enclosed content (tag pairs are essential in
  XML)
• Delimited by lt and /gt charactersltemailgtbwalla
  ce_at_megacorp.comlt/emailgt
• Allows for empty tags elements with no enclosed
  content marked up using trailing
  slashltnamegtRavi Vermaltbr/gtlt/namegt

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Elements

• Element attributes
• Elements, including empty elements, may have
  attributes associated with them
• These are name, value pairsltbookgtlttitle
  languageEnglishgtRoad Aheadlt/titlegtltprice
  currencyEurogt420.12lt/pricegtlt/bookgt
• Values are always in quotes (single or double)
• Any number of attributes
• Element names are case sensitive

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Elements

• Element identifiers XML allows unique
  identifiers to elements, as the value of some
  attributeltstate idTNgt ltsnamegtTamil
  Nadult/snamegtlt/stategtltcity idCHNgtltcnamegtChen
  nailt/cnamegtltstate-of idrefTN/gtlt/citygt

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Text

• PCDATA (parsed character data)
• XML documents store data as text, as a string of
  characters
• No distinction is made between numeric and
  character values
• Noted as PCDATA (parseable character data)
• Text data may not contain reserved characters
  (lt,gt,,,). Entity references must be used to
  represent these (e.g. lt for lt)
• CDATA
• Used for storing data that may contain the
  delimiters
• Delimited by lt!CDATA and gt

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Entity References

• Entity references within XML documents
• Delimited by and
• Internal entity reference
• Simple macros used for defining replacement text
  in XML documents (e.g. edi for Electronic
  Data Interchange)
• External entity references
• Referred entity lies outside the XML document
  (e.g. database)
• Parameter entity references
• Used in DTD allow grouping of components for
  easy reference (e.g. pe to include elements A,
  B and C.
• Delimited by and

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Comments and Processing Instructions

• Comments
• Text strings delimited by lt!-- and --gt
• Can be found anywhere in the XML document
• Processing instructions
• Messages for processing applications
• Examplelt?myprog sortalpha?gt

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Inside XML DTD

• DTD defines the document hierarchy in terms of
  the elements, elements themselves and their
  syntactic structure, entities and rules for their
  usage
• This is used for validating XML documents
  Examplelt!--DTD for Books--gtlt!ENTITY cright
  "169"gtlt!ELEMENT books (book)gtlt!ELEMENT book
  (title, isbn, authors, description?,price)gtlt!ELEM
  ENT title (PCDATA)gtlt!ATTLIST title lang
  (englishfrench) REQUIREDgtlt!ELEMENT isbn
  (PCDATA)gtlt!ELEMENT authors (PCDATA)gtlt!ELEMENT
  description (PCDATA)gtlt!ELEMENT price
  (PCDATA)gtlt!ATTLIST price curr (RsDollar)
  IMPLIEDgt

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Well Formed and Valid XML Document

• Well formed XML documents must be syntactically
  correct. What does this mean?
• There is only one Root element and it contains
  the documents content
• Match start-tags with end-tags (except for empty
  element tag)
• Nested elements never overlap
• Attributes are unique and values are in quotes
• Only entity references permitted are amp for
  , lt for lt, gt for gt, apos for , and
  quot for .

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Well Formed and Valid XML Document

• Valid XML documents
• Valid XML documents are well-formed XML documents
  which include an XML declaration and document
  type declaration
• Valid documents must also adhere to the DTD

Lets look at an example using sample Medline
XML document
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Rendering of XML

• How can we view XML documents on the Web?
• XML is about data, not presentation
  presentation has to be handled separately
• This can be handled using CSS (Cascading Style
  Sheets) and XSLT (Extensible Stylesheet Language
  Transformations)
• CSS and XSLT can be used for rendering XML
  documents on the Web
• IE 5.0 supports viewing XML document trees and
  HTML rendering using CSS
• Lets see a CSS example (syllabus2)

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Creating and Processing XML Documents

• XML documents can be created using any text
  editor
• XML editors and browsers are also available (e.g.
  Softquads Xmetal, XMLSPY)
• Complete publishing solutions are also available
  (e.g. Cocoon in Java)
• Computers (applications) can exchange XML data
  and process these using DTD for extraction and
  validation
• API specifications are also available for
  simplifying XML document processing (e.g. W3Cs
  DOM specification)
• Most RDBMS packages have begun to support import/
  export of SQL database content in XML format

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XML Applications and Vocabularies

• XML has found rapid use in a large number of
  domains
• Domain-specific vocabularies (DTDs and processing
  tools, techniques, practices) have been developed
• Mathematics MathML
• Chemistry CML
• Instruments Markup Language IML
• BioInformatics Sequence Markup Language (BSML)
• E-Books Specs developed by Open eBook forum
• Medicine Health Level 7
• Business/e-commerce eXML, BizTalk
• Mobile communications - WML

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XML and Bibliographic Information

• XML appears to be made for documentary
  information (bibliographic or full text) since
  document content is already structured XSLT can
  be used for viewing, transforming and presenting
  the content in different ways
• Several bibliographic databases are now available
  in XML (e.g. Medline, MARC)
• Journal publishers are also embracing XML (e.g.
  IOP)
• Digital publishing Books and other full-text
  documents mark-up once and view differently
• e.g. Tobacco war book in escholarship website
  in the California Digital Library
• Interoperability among digital libraries OAI
  initiative in using MARC XML for interoperability
  among DLs

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Related Specifications and Standards

• XSL (Extensible Stylesheet Language) way to
  specify stylesheets with XML for presentation
  and rendering (formatting) also a language for
  conversion of documents with different DTDs
• XLL (Extensible Linking Language) XML linking
  and addressing linking language (XLink) and
  addressing language (XPointer)
• XHTML Formulation of HTML 4.0 as an XML 1.0
  application Extensible HyperText Markup Language
• XQL XML oriented query language (under
  formulation)
• XML Schema Schema language for supporting user
  defined data types (e.g. integers) something
  not possible with DTD

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Related Specifications and Standards

• DOM (Document Object Model) XML documents will
  be manipulated by web applications, for request
  parsing and building responses. DOM is an API for
  this. Specifies a set of objects and interfaces
  for manipulating HTML and XML documents. DOM
  provides a tree-structured view of the document
  enabling XML parsers to construct a tree of
  objects in memory.
• Namespaces Web applications may need to work
  with different XML documents having different
  DTDs these might use same element names for
  different entities and different names for same
  entity name collisions and heterogeneity.
  Namespaces specification is expected to resolve
  this problem.

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XML Resources

• www.oasis-open.org/cover/ (Robin Covers SGML/XML
  page)
• www.xml.com
• www.ucc.ie/xml/ (XML FAQ and links to other
  topics related to XML)
• www.w3.org/XML/
• IBM Developerworks www.ibm.com/developer/xml/
• Microsoft XML Developer Center
  msdn.microsoft.com/xml/default.asp
• XML4Lib A discussion forum related to XML use on
  librarieshttp//sunsite.berkeley.edu/XML4Lib/