Post on 17-Oct-2014
description
1
Gegevensbanken“Laatse Les”
Prof. Erik Duval2009 - 2010
Sunday 30 May 2010
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Sunday 30 May 2010
• NoSQL (Met dank aan Steven Noels)
• XML (met dank aan prof. Olivié!)
• over het examen...
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Sunday 30 May 2010
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://en
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Sunday 30 May 2010
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Sunday 30 May 2010
8 http://www.w3c.it/talks/2005/openCulture/slide7-0.html
Sunday 30 May 2010
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://en
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Sunday 30 May 2010
XML is not ...• Extension of HTML
• XHTML is XML-compliant, and extensible
• Just for Web pages
• Useful when data are stored or exchanged
• Concerned with semantics
• XML does not define semantics, just syntax
• Innovative new technology
• Standard, building on existing technology
• Only a hype
• Though also 10
Sunday 30 May 2010
XML is ...• Endorsed by W3C and major companies
• Extensible
• No tag name limitations
• No language limitations
• Human software developer-readable
• Can be processed with basic text tools
• Open standard
• no vendor lock-in (in theory...)
• Easy to implement
• powerful, cheap (free), off-the-shelf XML tools11
Sunday 30 May 2010
• 1969: SGML (Standard Generalized Markup Language)
• Meta-language: describe other languages
• Powerful, but rather complicated
• 1986: ISO standard
• 1992: HTML (HyperText Markup Language)
• Based on SGML
• Simple, but limited
• 1996: Start design of XML
• By World Wide Web Consortium (W3C)
• 1998: Publication of XML 1.012
Sunday 30 May 2010
Design Goals
• Easy to use over the Internet
• Power of SGML
• Simplicity of HTML
• Human-legible
• Easy to create
• Compactness is not an issue
• “The ASCII of the Web”13
Sunday 30 May 2010
XML Basics<Person>
<Name>
<First>Thomas</First>
<Last>Atkinson</Last>
</Name>
<Age>30</Age>
</Person>
• Self-defined, meaningful tags
• Separate data and its representation14
Sunday 30 May 2010
• Language for defining syntax
• Records and fields have explicit boundaries
• parse-able without knowing structure (self-descriptive)
• Unicode support (UTF-8, UTF-16, ...)
• Web-aware
• DTD, ENTITY and Schema can be loaded through URL
• Strictly parsed: no ambiguity (case sensitive!)
• Extensible: namespaces
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Sunday 30 May 2010
<?xml version="1.0” encoding=“UTF-8”?> <!-- processing instruction: XML follows --><!DOCTYPE addressbook SYSTEM "http://www/~koenh/ddml/addressbook.dtd”> <!-- Document Type Declaration... --> <!-- ExternalDTDPointer --><addressbook> <!--root element --> <person first-name="John" family-name="Doe” employee-number="1234"> <contact-info> <email address="Jdoe@home.com"/> </contact-info> <address street="Celestijnenlaan” number="200A"/> </person></addressbook>
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Sunday 30 May 2010
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<H1 align=”center” > a Heading </H1>
attribute
openingtag
openingtag
openingtag
content closing tag
elementelementelementelementelement
Sunday 30 May 2010
• Cfr. HTML markup tags
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<H1 align=”center” > a Heading </H1>
attribute
openingtag
openingtag
openingtag
content closing tag
elementelementelementelementelement
Sunday 30 May 2010
• Cfr. HTML markup tags
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<H1 align=”center” > a Heading </H1>
attribute
openingtag
openingtag
openingtag
content closing tag
elementelementelementelementelement
Sunday 30 May 2010
• Cfr. HTML markup tags
17
<H1 align=”center” > a Heading </H1>
attribute
openingtag
openingtag
openingtag
content closing tag
elementelementelementelementelement
Sunday 30 May 2010
• Cfr. HTML markup tags
17
<H1 align=”center” > a Heading </H1>
attribute
openingtag
openingtag
openingtag
content closing tag
elementelementelementelementelement
Sunday 30 May 2010
• Cfr. HTML markup tags
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<H1 align=”center” > a Heading </H1>
attribute
openingtag
openingtag
openingtag
content closing tag
elementelementelementelementelement
Sunday 30 May 2010
• Cfr. HTML markup tags
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<H1 align=”center” > a Heading </H1>
attribute
openingtag
openingtag
openingtag
content closing tag
elementelementelementelementelement
Sunday 30 May 2010
• Cfr. HTML markup tags
• Major differences:
• Case sensitive
• Proper nesting: No <A> … <B> … </A> … </B>
• Unicode instead of ASCII17
<H1 align=”center” > a Heading </H1>
attribute
openingtag
openingtag
openingtag
content closing tag
elementelementelementelementelement
Sunday 30 May 2010
Vocabularies
• Agreed-upon XML tag sets for specific domain
• Examples
• Chemical Markup Language (CML)
• Business: ebXML, RosettaNet, BizTalk
• Mathematics: MathML
• Multimedia: Synchronized Multimedia Integration Language (SMIL)
• Etc.
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Sunday 30 May 2010
• well-formed: follows XML syntax
• Proper tag and attribute names
• Tags properly closed
• Attributes and text between tags do not contain ‘<‘ (escape with <)
• valid: well-formed and vocabulary
• All elements and their attributes declared in DTD
• Attribute values follow DTD type declarations
• CDATA, ID, IDREF, IDREFS, NMTOKEN, NMTOKENS, enumerated
• Nesting and sequencing of elements follows DTD19
Sunday 30 May 2010
Elements• XML’s container for
• Attributes
• Character data
• Other elements (“child” elements)
• Delimited by opening and closing tags
• Non-empty element: <name>..</name>
• Empty element: <name/>
• Form a simple hierarchic tree
• Root = “document element”20
Sunday 30 May 2010
Attributes and Strings
• Attributes
• Name-value pairs: name=value
• Only strings as value!
• Strings
• Enclosed by ‘...’ or “...”→ replace with ' or "
• Character data
• Any text that is not markup
• ‘&’, ‘<’ and ‘>’ are markup → replace with & < and >
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Sunday 30 May 2010
Document structure
• Prolog (optional)• <?xml version="1.0” encoding=“UTF-8”?>
• version="number" (compulsory)
• encoding="character encoding" (optional)
• Document type declaration• <!DOCTYPE document_element ... >
• Body–The document element
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Sunday 30 May 2010
Another example<?xml version="1.0" standalone="no"?>
<!DOCTYPE BankAccounts ...>
<!-- This is an example XML document -->
<BankAccounts>
<Account accountNr="123-456789-01" use="personal">
<Owners> <Person ID="1258-a8d72-98"> <Name>John Smith</Name></Person>
<Person ID="5842-df5ef-e9"> <Name>Claudia Scott</Name></Person>
</Owners>
<CreditCards><CreditCard number="12345"/></CreditCards>
<Balance Currency="EUR">50000</Balance>
</Account>
...
</BankAccounts> 23
Sunday 30 May 2010
Document Type Definition
<!ELEMENT address EMPTY> <!-- no content, used for attributes only -->
<!ATTLIST address city CDATA #REQUIRED <!-- character data: any string --> <!-- value for that attribute must be present -->
state NMTOKEN #REQUIRED <!-- name token: letters, numbers, ., -, _ and : only -->
number CDATA #REQUIRED street CDATA #REQUIRED>
<!ELEMENT addressbook (person+)> <!-- 1 or more -->
<!ELEMENT contact-info (home-phone|mobile-phone|email)*> <!-- choice --> <!-- o or more -->
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Sunday 30 May 2010
Document Type Definition<!ELEMENT email EMPTY><!ATTLIST email address CDATA #REQUIRED>
<!ELEMENT home-phone EMPTY><!ATTLIST home-phone number CDATA #REQUIRED>
<!ELEMENT job-info EMPTY><!ATTLIST job-info is-manager (yes|no) 'no’ <!-- default -->
emp-type (FullTime|PartTime) 'FullTime’ job-description CDATA #REQUIRED>
<!ELEMENT misc-info (#PCDATA)> <!-- Parsed Character Data: cannot contain subelements -->
<!ELEMENT mobile-phone EMPTY><!ATTLIST mobile-phone number CDATA #REQUIRED>25
Sunday 30 May 2010
Document Type Definition
<!ELEMENT manager EMPTY><!ATTLIST manager empnumber IDREF #REQUIRED> <!-- reference to empnumber of person -->
<!ELEMENT person (contact-info,address, job-info?,manager?,misc-info?)> <!-- sequence --> <!-- zero or one -->
<!ATTLIST person first-name CDATA #REQUIRED middle-initial CDATA #IMPLIED <!-- can, but need not be provided -->
employee-number ID #REQUIRED <!-- can be referred to by manager.empnumber -->
family-name CDATA #REQUIRED>
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Sunday 30 May 2010
namespaces: problem
<widget type="gadget">
<head size="medium"/>
<big><subwidget ref="gizmo"/></big>
<info>
<head><title>Gadget</title></head>
<body><h1>Gadget</h1>
A gadget contains a big gizmo
</body>
</info>
</widget>
Name collision!
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Sunday 30 May 2010
namespaces: approach
• A collection of names, identified by a URI reference, which are used in XML documents as element types and attribute names
•xmlns:prefix="URI"
• URI used only as identifier
• does not need to point to anything
• applies to all nested elements and attributes
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Sunday 30 May 2010
namespaces: example<widget xmlns="http://www.widget.org"
xmlns:xhtml="http://www.w3.org/TR/xhtml1"
type="gadget">
<head size="medium"/>
<big><subwidget ref="gizmo"/></big>
<info><xhtml:head><xhtml:title>Gadget
</xhtml:title></xhtml:head>
<xhtml:body><xhtml:h1>Gadget
</xhtml:h1>A gadget contains...
</xhtml:body></info>
</widget> 29
Sunday 30 May 2010
Another example
<Address><Street>Celestijnenlaan</Street>
<Nr>200A</Nr> <City>Heverlee-Leuven</City> <Country>Belgium</Country></Address>
<Server><Name>www</Name><Address> 134.58.43.1 </Address>
</Server>
?30
Sunday 30 May 2010
Another example (2)
<Address xmlns="www.all.edu/departments"> <Street>Celestijnenlaan</Street> <Nr>200A</Nr> <City>Heverlee-Leuven</City> <Country>Belgium</Country></Address>
<Server xmlns="www.dns.net/servers"> <Name>www</Name> <Address> 134.58.43.1 </Address></Server>
<Department xmlns:edu="www.all.edu/departments" xmlns:dns="www.dns.net/servers"> <edu:Address> <Street>Celestijnenlaan</Street> ... </edu:Address> <dns:Name>www</dns:Name> <dns:Address>134.58.43.1</dns:Address></Department>
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Sunday 30 May 2010
Accessing XML documents
• Manual text file manipulation
• Cumbersome & Error-prone
• Parser
• Simplifies document manipulation
• Ensures proper grammar, well-formedness
• Abstracts content from grammar
• Accessed through standard API
• Document Object Model (DOM)
• Simple API for XML (SAX)32
Sunday 30 May 2010
• DOM parser
• create DOM object tree
• SAX parser
• generates events when elements encountered
• one-pass translation
• no need to keep whole document tree in memory
• Both can be validating or non-validating
• Many available(most freeware, open source)
• ibm xml4j, apache xerces, sun parser, microsoft, datachannel, oracle, ...
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Sunday 30 May 2010
DOM approach
http://java.sun.com/xml/jaxp/dist/1.1/docs/tutorial/overview/3_apis.html#JAXP34
Sunday 30 May 2010
DOM Node Tree
<?xml version="1.0"?><!-- An example XML document -->
<BankAccounts> <Account accountNr="123-456789-01“> <Owner ID="1258-a8d72-98"> John Smith </Owner> <Balance Currency="EUR"> 50000 </Balance> </Account> <Account ...> ...</BankAccounts>
Doc
Com An example XML document
El BankAccounts
El Account
Att accountNr = “123-456789-01”
El Owner = “John Smith”
Att ID = “1258-a8d72-98”
El Balance = “50000”
Att Currency = “Eur”
El Account...
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Sunday 30 May 2010
parsing: DOM
public void print(Node node) {
...
NodeList nlist=node.getChildNodes();
if (nlist != null) {
int l = nlist.getLength();
for (int i=0; i<l; i++) {
print(nlist.item(i));
...
}...}...}36
Sunday 30 May 2010
Dom Benefits & Drawbacks
• Benefits
• W3C Recommendation
• Language- and platform-independent
• Random access
• Intuitive
• Drawback
• Entire object tree in memory37
Sunday 30 May 2010
Simple API for XML (SAX)
• Not an official standard
• Ad-hoc product by XML developers
• Primarily Java API
• Event-based mechanism
• Don’t call the parser, the parser calls you
• No object model in memory
• Programmer must keep state information
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Sunday 30 May 2010
SAX approachht
tp://
java
.sun
.com
/xm
l/jax
p/di
st/1
.1/d
ocs/
tuto
rial
/ove
rvie
w/3
_api
s.ht
ml#
JAX
P
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Sunday 30 May 2010
SAX parsing modelApplication
Parser
ContentHandlernew ContentHandler()
new Parser()
setContentHandler()
parse()
startDocument()
startElement()
characters()
endElement()
endDocument()
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Sunday 30 May 2010
parsing: SAX$xml_parser = xml_parser_create();
xml_set_element_handler($xml_parser,
"startQuestion","endQuestion");
...
xml_parse($xml_parser,$data,feof($fp))
...
function startQuestion($parser,$name,$attrs) {
...if ($name == "QUESTION")
...new Question($attrs["QTEXT"]);
... 41
Sunday 30 May 2010
• Start and end of document
–startDocument()
–endDocument()
• Start and end of element
–startElement(namespace, name, qname, attlist)
–endElement(namespace, name, qname)
• Character data
–characters(char[] ch, int start, int length)
• Processing Instruction
–processingInstruction(target, data)
• No event for comments!42
Sunday 30 May 2010
Another SAX example<?xml version="1.0" standalone="no"?>
<!DOCTYPE BankAccounts ...>
<!-- This is an example XML document -->
<BankAccounts>
<Account accountNr="123-456789-01" use="personal">
<Owners>
<Person ID="1258-a8d72-98"><Name>John Smith</Name></Person>
<Person ID="5842-df5ef-e9"><Name>Claudia Scott</Name></Person>
</Owners>
<CreditCards><CreditCard number="12345"/></CreditCards>
<Balance Currency="EUR">50000</Balance>
</Account>
...
</BankAccounts> 43
Sunday 30 May 2010
public class AvgBalanceCalculator extends DefaultHandler {private double total = 0.0; private int count = 0; private boolean isBalance = false;
public void startElement(String uri, String name, String qname, Attributes atts) {if (name.equals(“Balance")) { isBalance = true; count++; }}
public void characters(char[] ch, int start, int len) throws SaxException {if (isBalance) { String help = new String(ch, start, len); double balance = (new double(help)).doubleValue(); total = total + balance; isBalance = false; }}
public void endDocument() {if (count != 0)
System.out.println(“Average balance is ”+(total/count)); }}
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Sunday 30 May 2010
SAX Benefits & Drawbacks• Benefits
• Suitable when
• parsing large documents
• constructing proprietary object structures
• only small subset of information is needed
• Simple and fast
• Drawbacks
• Read-only
• No random access
• Complex searches messy to program45
Sunday 30 May 2010
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beperkingen van DTDs
• geen typering van tekst elementen en attributen
• alle waarden zijn strings, geen integers, reals, enz.
• ongeordende verzameling van subelementen moeilijk te definiëren
• orde is meestal irrelevant in gegevensbanken
• IDs en IDREFs zijn niet getypeerd
• het DNO attribuut van een EMPLOYEE kan een referentie bevatten aan een andere EMPLOYEE, wat zinloos isvb. <EMPLOYEE SSN="_888665555 " SEX="M" DNO="_888665555 ">
• het DNO attribuut zou als beperking moeten hebben dat het slechts aan een DEPARTMENT kan refereren
Sunday 30 May 2010
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XML Schema
• typering van waarden
• vb. integer, string, enz.
• ook beperkingen op min/max waarden
• types door gebruiker gedefinieerd
• is gespecificeerd in XML syntax,
• meer gestandaardiseerde voorstelling
• is geïntegreerd met namespaces
• en nog andere mogelijkheden
• lijst types, uniciteitsbeperking op sleutels, verwijssleutelbeperkingen, overerving,…
Sunday 30 May 2010
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XSDL
• XML Schema Definition Language
• documenten met suffix .xsd
Sunday 30 May 2010
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XML Schema: voorbeeldXML schema
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">....<xsd:element name="PWORKER" minOccurs="0" maxOccurs="unbounded"> <xsd:complexType> <xsd:sequence> <xsd:element name="HOURS" type="xsd:float"/> </xsd:sequence> <xsd:attribute name="SSN" type="xsd:IDREF" use="required"/> </xsd:complexType></xsd:element>....</xsd:schema>
XML instantie
<PWORKER SSN="_123456789"> <HOURS>7.5</HOURS> </PWORKER>
Sunday 30 May 2010
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XML: eenvoudige types– ingebouwde eenvoudige types
• string, integer, decimal, float, boolean, date, time,…
• <xsd:element name=“gebdat” type=“xsd:date” />
– door gebruiker gedefinieerde eenvoudige types
• gedefinieerd met simpleType element
• restriction element geeft het basistype waarop gesteund is
• <xsd:simpleType name=“salaryRange”> <xsd:restriction base=“xsd:integer”> <xsd:minInclusive value=“25000” /> <xsd:maxInclusive value=“100000” /> </xsd:restriction></xsd:simpleType>
Sunday 30 May 2010
XML: eenvoudige types<xsd:simpleType name=“studentClassificatie”> <xsd:restriction base=“xsd:string”> <xsd:enumeration value=“bachelorstudent” /> <xsd:enumeration value=“masterstudent” /> <xsd:enumeration value=“doctorstudent” /> </xsd:restriction></xsd:simpleType>
<xsd:simpleType name=“deptType”> <xsd:restriction base=“xsd:string”> <xsd:length value=“3” /> </xsd:restriction></xsd:simpleType>
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XPath (example)/COMPANY/EMPLOYEE
ROOT
COMPANY
EMPLOYEE
SSN
_333445555
EMPLOYEE
SSN
_123456789
EMPLOYEE
SSN
_999887777
Sunday 30 May 2010
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/COMPANY/EMPLOYEE
ROOT
COMPANY
EMPLOYEE
SSN
_333445555
EMPLOYEE
SSN
_123456789
EMPLOYEE
SSN
_999887777
Sunday 30 May 2010
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/COMPANY/EMPLOYEE
ROOT
COMPANY
EMPLOYEE
SSN
_333445555
EMPLOYEE
SSN
_123456789
EMPLOYEE
SSN
_999887777
Sunday 30 May 2010
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/COMPANY/EMPLOYEE
ROOT
COMPANY
EMPLOYEE
SSN
_333445555
EMPLOYEE
SSN
_123456789
EMPLOYEE
SSN
_999887777
Sunday 30 May 2010
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/COMPANY/EMPLOYEE
ROOT
COMPANY
EMPLOYEE
SSN
_333445555
EMPLOYEE
SSN
_123456789
EMPLOYEE
SSN
_999887777
Sunday 30 May 2010
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XPath/COMPANY/EMPLOYEE
ROOT
COMPANY
EMPLOYEE
SSN
_333445555
EMPLOYEE
SSN
_123456789
EMPLOYEE
SSN
_999887777
<EMPLOYEE SSN="_123456789" SEX="M“ SUPERSSN="_333445555" DNO="_5">
<FNAME>John</FNAME> <MINIT>B</MINIT>
....</EMPLOYEE>
<EMPLOYEE SSN="_333445555" SEX="M“ SUPERSSN="_888665555" DNO="_5">
<FNAME>Franklin</FNAME> <MINIT>T</MINIT>
<LNAME>Wong</LNAME> <BDATE>08-DEC-45</BDATE>
</EMPLOYEE><EMPLOYEE SSN="_999887777" SEX="F“ SUPERSSN="_987654321" DNO="_4">
<FNAME>Alicia</FNAME>
.....
Sunday 30 May 2010
XML family of technologies
• Xlink: hypertext
• XSL: Extensible Style Sheet Language
• XSL-T Transformation
• Formatting Objects
• Xschema: additional constraints on attribute types
• and more...
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Sunday 30 May 2010
XML applications
• RDF: Resource Description Framework
• infra
• XHTML: eXtensible HTML en HTML5
• XML compliant HTML
• MathML
• SMILE: synchronized multimedia presentation
• Many others
• Chemical Markup Language, Vector Graphics Markup Language, Open Software Description Format, Weather observation, astronomical data, financial data, electronic components, workflow, business cards, real estate, newspaper, classifieds, javadoc, human resource, advertising, architecture ….
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Sunday 30 May 2010
XML Working Groups• XML Coordination
• XML Core
• XSL (XSLT, XSL/FO) -> W3C architecture
• Efficient XML Interchange
• XML Processing Model
• XML Query (XQuery, XPath)
• XML Schema
• Service Modeling Language (SML)64
Sunday 30 May 2010
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More XPath Features• Operator “|” used to implement union
• E.g. //EMPLOYEE[count(DEPENDENT) = 1] | //EMPLOYEE[not(DEPENDENT)]
• gives employees with either 0 or 1 dependents
• “//” can be used to skip multiple levels of nodes
• E.g. /COMPANY//FNAME
• finds any FNAME element anywhere under the /COMPANY element, regardless of the element in which it is contained.
• A step in the path can go to:
parents, siblings, ancestors and descendants
of the nodes generated by the previous step, not just to the children
• “//”, described above, is a short from for specifying “all descendants”
• “..” specifies the parent.
• e.g. : /COMPANY//FNAME/../BDATESunday 30 May 2010
• laat toe om meer algemene queries te formuleren dan XPath
• algemene vorm: FLWOR uitdrukking
FOR < for-variabele > IN < in-uitdrukking >
LET < let-variabele > := < let-uitdrukking >
[ WHERE < filter-uitdrukking > ]
[ ORDER BY < orde-specificatie > ]
RETURN < uitdrukking >
• opm: FOR en LET kunnen alleen of samen voorkomen66
XQuery
Sunday 30 May 2010
67
• Q1: voornaam en familienaam van alle werknemers die meer dan 70000 verdienen
• FOR $x IN doc(www.company.com/info.xml)// employee [employeeSalary > 70000] / employeeNameRETURN < res > $x / firstName, $x / lastName </ res >
• alternatief:FOR $x IN doc(www.company.com/info.xml)company / employeeWHERE $x / employeeSalary > 70000RETURN < res > $x / employeeName / firstName, $x / employeeName / lastName </ res >
Sunday 30 May 2010
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• Q3: voornaam en familienaam van alle werknemers die meer dan 20 uur op project nummer 5 werken, met dat aantal uren
• FOR $x IN doc(www.company.com/info.xml)/ company / project [projectNumber = 5] / projectWorker ,$y IN doc(www.company.com/info.xml) / company / employeeWHERE $x/hours > 20.0 AND $y.ssn = $x.ssnRETURN < res > $y / employeeName / firstName, $y / employeeName / lastName,$x / hours </ res >
Sunday 30 May 2010
The End...
Bedankt!Vragen...?
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Sunday 30 May 2010
NoSQL
• non-relational
• distributed
• open source
• horizontally scalable
• “web scale”
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Sunday 30 May 2010
NoSQL
• non-relational
• distributed
• open source
• horizontally scalable
• “web scale”
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• schema free
• easy replication
• simple API
• BASE (not ACID)
Sunday 30 May 2010
Systems
• Core: Hadoop, HBase, Cassandra, Hypertable, ...
• Docs: CouchDB, MongoDB, Riak, Terrastore, ...
• Key-Value, tuple: Amazon SimpleDB, Azure, ...
• Graph: Neo4J, Bigdata, InfoGrid, HyperGraph, ...
• Object: Versant, Perst, ZODB, ...
• Grid: GigaSpaces, Hazelcast, ...
• XML: Tamino, eXist, Mark Logic, Xindice, ...
• ...71 http://nosql-databases.org/
Sunday 30 May 2010
nosql
• Google BigTable
• Amazon Dynamo
• Open source: HBase
• Cassandra: last.fm, FaceBook
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Sunday 30 May 2010
nosql: why
• big data sets:
• Digg green badge: 3 TB
• Facebook inbox: 50 TB
• eBay overall data: 2 PB
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http://about.digg.com/blog/looking-future-cassandra
Sunday 30 May 2010
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http://about.digg.com/blog/looking-future-cassandra
Sunday 30 May 2010
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http://about.digg.com/blog/looking-future-cassandra
14 seconds
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75http://about.digg.com/blog/looking-future-cassandra
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Text
http://www.slideshare.net/oemebamo/database-sharding-at-netlog-presentation
Sunday 30 May 2010
no attempt to ACID
• Atomicity
• Consistency
• Isolation
• Durability
• trade ACID off in favor of high availability
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Sunday 30 May 2010
query
• associative array, key-value pair
• XQuery
• SPARQL
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Sunday 30 May 2010
Vragen...?
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