II. XML Data Management

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II. XML Data Management
A XML refresher using material from
A. Silverschatz and M. Sapossnek B - XML-Data
Management (1) Query languages XPATH,
XQuery, SQLX C - Mapping XML data to
databases - Native XML Data management

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What is XML?

• Acronym for eXtensible Markup Language
• Syntax for structuring data and documents in
  human-readable form
• THE "Syntax of the WEB"
• Meta language for defining languages
• Bases of many extensions
• Namespaces
• Stylesheets
• Hyperlinks
• Schemata
• Standardized by W3Chttp//www.w3.org/TR/REC-xml

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What XML is Not..

• No protocol
• Language for describing data
• Used as data format in protocols
• Protocols may be syntactically defined by XML
• No programming languagebut
• XML documents may contain code fragments
• New languages allow for XML code as part of the
  language (Xen, a MS extension of C )
• Some XML extensions with superimposed PL
  semantics,rule semantics in XSLT
• No magic semantics
• Interpretation by humans, applications,
  standards derived from XML

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Why XML?

• not a question any more, since widely adopted
• Simple
• Extensible
• Easy to process
• Easy to generate
• Data interchange critical for networked
  applications

"XML will be the ASCII of the Web basic,
essential, unexciting" Tim Bray
... it is already
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XML example

• Pre-XML representation of data
• XML representation of the same data

PO-1234,CUST001,X9876,5,14.98
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XML example

• Graphical representation

PURCHASE_ORDER
PO_NUM
Cust_ID
QUNTY
PO-1234
CUST001
XML documents - tree structured - Data an
metadata in the same document (as
opposed to RDBS)
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XML Usage

• Two basic types of XML usage
• Document centric (document oriented)
• structuring a digital document, including logical
  layout
• primary focus of SGML - predecessor of XML
• Data centric
• Description of data in a self describing form for
  later processing
• Distinction not totally clear
• See purchase order example If typical document
  characteristic included (company addr.,customer
  addr, date, , company logo) it would be a
  document oriented usage of XML

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Document centric XML documents example
ltProductgt ltNamegtVariabler Maulschlüssellt/Namegt
ltDevelopergt Full Fabrication Labs, Inc.
lt/Developergt ltSummarygt Großer, verstellbarer
Schraubenschlüssellt/Summarygt ltDescriptiongt
ltParagtDer Engländer besteht aus erstklassigem
Stahl und besitzt einen gummierten
Handgriff. Die Maulgröße liegt zwischen 0
und 32 mm. lt/Paragt ltParagtSie können.....
lt/Paragt ltListgt ltItemgt ltLink
URL"Order.html"gt Bestellen lt/Linkgtlt/Itemgt
ltItemgt ltLink URL"Wrenches.htm"gt Andere Werkzeuge
ansehen lt/Linkgt lt/Itemgt ltItemgt
ltLink URL"catalog.zip"gt Den Katalog
herunterladen lt/Linkgt lt/Itemgt lt/Listgt
ltParagt Der Schraubenschlüssel kostet 15.33 Euro
inkl. MWSt. Wenn Sie jetzt bestellen,
erhalten Sie zusätzlich unsere wertlose
Hobbybastler-Fibel.lt/Paragt lt/Descriptiongt lt/Pro
ductgt
TypicalLong text elements
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Data centric XML documents example
ltOrdersgt ltSalesOrder SONumber"12345"gt
ltCustomer CustNumber"543"gt
ltCustNamegt ABC Industrieslt/CustNamegt
ltStreetgt 123 Main St.lt/Streetgt
ltCitygtChicagolt/Citygt ....
lt/Customergt ltLine LineNumber"1"gt
ltPart PartNumber"123"gt
ltDescriptiongt ltpgtltbgt Turkey
wrenchlt/bgtltbr /gt Stainless
steel, one-piece construction,
lifetime guarantee.lt/pgt
lt/Descriptiongt ltPricegt9.95lt/Pricegt
lt/Partgt
ltQuantitygt10lt/Quantitygt lt/Linegt
....... lt/SalesOrdergt lt/Ordersgt
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XML Syntax

• One, and only one, root element
• Sub-elements must be properly nested
• A tag must end within the tag in which it was
  started
• Attributes are optional
• Attribute values must be enclosed in or
• No data type but 'string'
• Processing instructions optional
• XML is case-sensitive
• lttaggt and ltTAGgt are not the same type of element

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Why hierarchical "data model"?

• Hierachies (nesting) in data bases? Why not?
• REDUNDANCY!
• Multiple items, customers, occur multiple times
  in different orders
• Normalization replaces redundancies by foreign
  keys
• OO / OR Data bases??
• Nesting useful in data transfer
• External application does not have access to
  foreign key / to database.

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XML Attributes vs Elements

• Distinction between subelement and attribute
• In the context of documents
• attributes are part of markup
• subelement contents part of the basic document
  contents
• In the context of data representation
  difference not clear, but confusing
• Same information can be represented in two ways
• ltaccount account-number A-101gt
• .
• lt/accountgt
• ltaccountgt ltaccount-numbergt A-101
  lt/account-numbergt
• lt/accountgt
• Suggestion use attributes for identifiers of
  elements use subelements for
  contents

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How to use XML data?

• Basic Idea

Applicationwith XML-Generator
DOM SAX
Receiving application
XML-Parser
Standard- Interfaces
How does application know about - syntactical
correctness - data semantics ?
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Correct or not correct ?
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Correctness of XML documents

• Syntactic correctness
• Conformance to XML syntax
• Document structured according to XML syntax is
  well-formed
• Compare Syntax checker for program
• Semantic correctness
• Given Meta level description of XML documents
  Document Type Definition (DTD) or XML Schema
• Document is valid with respect to DTD (Schema)
  if all definitions and restrictions have been
  fulfilled
• No DTD allowed, applications must know, what is
  meant
• What is semantics??
• Interpretation of tags is a matter of humans
  and/or the application program ltxyzgt could
  mean "book title" or "first name" or

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XML Namespaces

• Part of XMLs extensibility
• Allow autonomous users to differentiate between
  tags of the same name (using a prefix)
• Frees author to focus on the data and decide how
  to best describe it
• Allows multiple XML documents from multiple
  authors to be merged

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Namespace

• Examples
• No prefix all elements belong to same namespace

ltBOOK xmlnsbkhttp//www.bookstuff.org/bookinfo
gt ltbkTITLEgtAll About XMLlt/bkTITLEgt
ltbkAUTHORgtJoe Developerlt/bkAUTHORgt ltbkPRICE
currencyUS Dollargt19.99lt/bkPRICEgt
ltBOOK xmlnshttp//www.bookstuff.org/bookinfogt
ltTITLEgtAll About XMLlt/TITLEgt ltAUTHORgtJoe
Developerlt/AUTHORgt
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DTD and XML schema

• Type of XML document defined as
• DTD - not expressible in XML syntax
• XML schema
• Document Type Definition (DTD)
• Does not constrain types all values are
  strings in XML
• Syntax
• lt!ELEMENT elem (subelement-spec)gt
• lt!ATTLIST elem (attribute-specs) gt

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DTD elements and attributes

• Example (element decl)
• lt!ELEMENT depositor (customer-name
  account-number)gt
• lt!ELEMENT customer-name (PCDATA) gt
• lt!ELEMENT account-number (PCDATA) gt
• Subelements
• names of elements
• PCDATA (parsed character data), i.e., character
  strings
• EMPTY (no subelements) or ANY (anything can be a
  subelement)
• Subelement specification may have regular
  expressions
• lt!ELEMENT bank ( ( account customer
  depositor))gt
• Notation
• alternatives
• 1 or more occurrences ?
  "?" 0 or one
• 0 or more occurrences

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DTD example

• lt!DOCTYPE bank
• lt!ELEMENT bank ( ( account customer
  depositor))gt
• lt!ELEMENT account (account-number
  branch-name balance)gt
• lt!ELEMENT customer (customer-name
  customer-street customer-city)gt
• lt!ELEMENT depositor (customer-name
  account-number)gt
• lt!ELEMENT account-number (PCDATA)gt
• lt!ELEMENT branch-name (PCDATA)gt
• lt!ELEMENT balance (PCDATA)gt
• lt!ELEMENT customer-name (PCDATA)gt
• lt!ELEMENT customer-street (PCDATA)gt
• lt!ELEMENT customer-city (PCDATA)gt
• gt

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DTD attributes

• Attribute specification for each attribute
• Name
• Type of attribute
• CDATA
• ID (identifier) or IDREF (ID reference) or IDREFS
  
• more on this later
• Whether
• mandatory (REQUIRED) has a default value
  (value),
• or neither (IMPLIED)
• Examples
• lt!ATTLIST account acct-type CDATA checkinggt
• lt!ATTLIST customer
• customer-id ID REQUIRED
• accounts IDREFS REQUIRED gt

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DTD attribute ID

• At most one attribute of type ID per element
• ID attribute value of each element in an XML
  document must be distinct
• ID attribute value is object identifier
• attribute of type IDREF must contain the ID value
  of an element in the same document
• attribute of type IDREFS contains a set of (0 or
  more) ID values. ID value must contain the ID
  value of an element in the same document
• ID, IDREF, IDREFS do not designate a particular
  domain (no type!)

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DTD declaration

• External DTD-declarationlt?xml version"1.0"gtlt!DO
  CTYPE bank SYSTEM "http//www.x-ag.de/banks.dtd"gt
  ltbankgt ... lt/bankgt
• Internal DTD-declarationlt!DOCTYPE custDesc
  lt!ELEMENT custDesc (PCDATA)gt gtltcustDescgt
  consumer rights protagonist lt/custDescgt
• Mixed usagelt!DOCTYPE bank SYSTEM
  "http//www.x-ag.de/banks.dtd" lt!ATTLIST bank
  Descr CDATA REQUIREDgtgtltbank Descr" mostly
  private customers and ATM"gt ... lt/bankgt

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DTD limits

• No typing of text elements and attributes
• All values are strings, no integers, reals, etc.
• Difficult to specify unordered sets of
  subelements
• Order is usually irrelevant in databases
• (A B) allows specification of an unordered
  set, but
• Cannot ensure that each of A and B occurs only
  once
• How to express a, b and c in arbitrary order?
  lt!ELEMENT a ((b,c,d) (c,b,d) (b,d,c), ...)gt
  
• IDs and IDREFs are untyped
• The owners attribute of an account may contain a
  reference to another account, which is
  meaningless
• owners attribute should ideally be constrained to
  refer to customer elements

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XML Schema

• XML Schema (XSD) much more expressible Schema
  language compared to DTD schemas
• Typing of values
• E.g. integer, string, etc
• constraints on min/max values
• User defined types
• specified in XML syntax, unlike DTDs
• More standard representation, but verbose
• namespace support
• Many more features
• List types, uniqueness and foreign key
  constraints, inheritance Ability to map to RDB,
• significantly more complicated than DTD syntax
• Use of XSD recommended

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ltxsdschema xmlnsxsdhttp//www.w3.org/2001/XMLSc
hemagt ltxsdelement namebank typeBankType/gt lt
xsdelement nameaccountgtltxsdcomplexTypegt
ltxsdsequencegt ltxsdelement
nameaccount-number typexsdstring/gt
ltxsdelement namebranch-name
typexsdstring/gt ltxsdelement
namebalance typexsddecimal/gt
lt/xsdsquencegtlt/xsdcomplexTypegt lt/xsdele
mentgt .. definitions of customer and depositor
. ltxsdcomplexType nameBankTypegtltxsdsquencegt
ltxsdelement refaccount minOccurs0
maxOccursunbounded/gt ltxsdelement
refcustomer minOccurs0 maxOccursunbounded
/gt ltxsdelement refdepositor
minOccurs0 maxOccursunbounded/gt lt/xsdsequen
cegt lt/xsdcomplexTypegt lt/xsdschemagt
XSD example (from Silverschatz)
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Using XML

• Data exchange ?
• Data management
• Store, retrieve, query large document sets
  efficiently
• Today's solutions
• Mapping to RDB / ORDB / OODB
• "Native" XML data management (not necessarily
  very different from storing in conventional DB)
  
• Standardized data description different
  extensions and applications
• Bioinformatic Sequence Markup Language (BSML)
• MathML
• Scalable Vector Graphics (SVG).. And many, many
  more
• Ressource Description in the web (RDF)

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Using XML RDF with XML syntax
RDF-Modell
www.me.de/fritz
Homepage
Fritz Müller
Creator
Many of these triples form a graph
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Using XML

• Layout of documents?
• XML documents have logical structure
• Layout structure needed for output
• Use transformation language to describe device
  specific transformations

Transformation into all kinds of languages
(HTML, pdf, ) on all kinds of devices
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XML transformation

• XSLT The language used for converting XML
  documents into other forms
• Describes how the document is transformed
• Expressed as an XML document (.xsl)
• Template rules
• Patterns match nodes in source document
• Templates instantiated to form part of result
  document
• XPath for querying, sorting, etc.
• XSL-FO language for describing layout
• XSL XSLT XPATH XSL-FO

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XML transformation example (1)

• Document

ltsalesgt ltsummarygt ltheadinggtScootney
Publishinglt/headinggt ltsubheadgtRegional Sales
Reportlt/subheadgt ltdescriptiongtSales
Reportlt/descriptiongt lt/summarygt ltdatagt
ltregiongt ltnamegtWest Coastlt/namegt
ltquarter number"1" books_sold"24000" /gt
ltquarter number"2" books_sold"38600" /gt
ltquarter number"3" books_sold"44030" /gt
ltquarter number"4" books_sold"21000" /gt
lt/regiongt ... lt/datagt lt/salesgt
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XML transformation example (2)

• XSL style sheet - mapping to HTML

ltxslparam name"low_sales" select"21000"/gt ltBODY
gt lth1gtltxslvalue-of select"//summary/heading"/gt
lt/h1gt ... lttablegtlttrgtltthgtRegion\Quarterlt/thgt
ltxslfor-each select"//data/region1/quarter"gt
ltthgtQltxslvalue-of select"_at_number"/gtlt/thgt
lt/xslfor-eachgt ... ltxslfor-each
select"//data/region"gt lttrgtltxslvalue-of
select"name"/gtlt/thgt ltxslfor-each
select"quarter"gt lttdgtltxslchoosegt
ltxslwhen test"number(_at_books_sold lt
low_sales)"gt colorredlt/xslwhengt
ltxslotherwisegtcolorgreenlt/xslotherwisegtlt/xs
lchoosegt ltxslvalue-of select"format-number
(_at_books_sold,',')" /gt lt/tdgt
... lttdgtltxslvalue-of
select"format-number(sum(quarter/_at_books_sold),
',')"/gt
XPath expression XPath query language on doc
trees
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XML transformation example (2)

• The result