Dr. Alexandra I. Cristea acristea/ CS 253: Topics in Database Systems: C1.
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Dr. Alexandra I. Cristea
http://www.dcs.warwick.ac.uk/~acristea/
CS 253: Topics in Database Systems: C1
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Lecturers
• Alexandra I. Cristea
• Hugh Darwen: hughdarwen@gmail.com
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Schedule• Usual:
– Tue 13-14, CS104– Thu 13-14, CS104– Fri 13-14, CS104
• Exceptions:– Others: TBA: check forum, website, course
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Slides
• Thanks to:– W3C courses– Others: mentioned directly
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Contact
• Forum:
http://forums.warwick.ac.uk/wf/browse/forum.jsp?fid=2194 • IF (and ONLY IF) a question is personal, you
might address it to AIC, HD – FORMAT: subject of email should contain ‘CS253’
and topic of the email (otherwise it will be filtered out)
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Course site(s):
• Current:– http://www.dcs.warwick.ac.uk/~acristea/courses/CS
253/
– Will contain current slides, as taught at the course– Will contain notifications: check BEFORE & AFTER
the course
• Official:– http://www.dcs.warwick.ac.uk/undergraduate/modules/cs253
.html
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Content: Topics1. XML
2. XML Query languages
3. Temporal Data – Hugh Darwen
4. SQL: Missing Info without Nulls – Hugh Darwen
5. SQL: Concurrency
6. SQL: The “Askew Wall” – Hugh Darwen
7. Q&A, Exam preparation
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Books & Material• Online material from W3C and W3C schools a.o. (as
mentioned in the slides and notes check also the notes in the powerpoints)
• H. Darwen, An Introduction to Relational Database Theory, ISBN 978-87-7681-500-4 Bookboon
• Korth and Silberschatz, Database System Concepts, McGraw-Hill,1991.
• Ullman J D, Principles of Database Systems (Vols 1 and 2), Computer Science Press,1988.
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Purpose of this course
• A selection of topics related to databases
• A more modern view on current database implementation & research
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Overlaps and sequencing
• Form: optional
• Prerequisites – CS252: Fundamentals of Database Systems
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Organization of the course• 7.5 CATS• CS, CSE, CBS, Mathematics• ~ 15 1-hour lectures• Exam at the end: 2 hours• Rules of the game:
– Read also comments on the slides and additional reading material.
– Presence is optional, but beware: slides-only are NOT ENOUGH to learn from for the exam; you need to participate, take your own notes, so self-study!
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Scope of CS 253
• A selection of topics on current database systems,• As well as a selection of topics not covered in the
fundamental course part
• What this course is not:– This course is not an exhaustive course on database
topics– This course has no seminars or practical part, so it is
based on lectures and self-study only
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XML
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XML history
• Inception: circa 1996
• The Extensible Markup Language (XML) became a W3C Recommendation 10. February 1998.
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What is XML?• XML stands for EXtensible Markup
Language • XML was designed to describe data • XML is more of a standard and
supporting structure than a standalone programming language
• XML is a markup language much like HTML – wrong!: meta-language
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How does XML work?
• XML tags are not predefined. You must define your own tags
• XML uses a Document Type Definition (DTD) or an XML Schema to describe the data
• XML with a DTD or XML Schema is designed to be self-descriptive
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XML is Free and Extensible• XML tags are not predefined. You must
"invent" your own tags.• The tags used to mark up HTML documents
and the structure of HTML documents are predefined. The author of HTML documents can only use tags that are defined in the HTML standard (like <p>, <h1>, etc.).
• XHTML is XML but not vice-versa.
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XML does not DO anything• XML was created to structure, store and to send
information
<note> <to>John</to> <from>Jane</from>
<heading>Reminder</heading> <body>Don't forget the book!</body>
</note>
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Main Difference XML, HTML• XML was designed to carry data.• XML is not a replacement for HTML.
XML and HTML were designed with different goals:– XML was designed to describe data and to focus on what
data is.
– HTML was designed to display data and to focus on how data looks.
• HTML is about displaying information, while XML is about describing information.
• Syntax: XML is well formed, just like XHTML
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XML is a Complement to HTML
• XML is not a replacement for HTML.– In future Web development it is most likely
that XML will be used to describe the data, while HTML will be used to format and display the same data.
• XML is a cross-platform, software and hardware independent tool for transmitting information.
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Benefits XML• extensibility and structured nature of XML
allows it to be used for communication between different systems
• from one source of XML-based information you can format and distribute it via a multitude of different channels – XSL files act as templates, allowing a single
stylesheet to be used to format multiple pages or the same content for multiple distribution channels
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XML in Future Web Development
• XML is starting to be everywhere.
• the XML standard has been developed quickly and a large number of software vendors have adopted it.
• XML might be the most common tool for all data manipulation and data transmission.
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XML Can be Used to Create New Languages• XML is the mother of WAP and WML.
– WAP: standard for web browser for mobile devices
– The Wireless Markup Language (WML), used to markup Internet applications for handheld devices like mobile phones, is written in XML.
• And many others …
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• Question: When should I use XML?
• Answer: When you need a buzzword in your resume.
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Viewing XML• to view XML documents hierarchically or view
their output, you need an XML parser and processor.
• there are a number of these tools available:• See examples at: • http://www.stylusstudio.com/xml_download.html • http://www.w3schools.com/xml/xml_parser.asp • Please note, however: XML was not designed to
display data.
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The basic XML flow
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XML Rules1. Every start-tag must have a matching end-tag.
2. Tags cannot overlap. Proper nesting is required.
3. XML documents can only have one root element.
4. Element names must obey the following XML naming conventions: a) Names must start with letters or the "_" character.
Names cannot start with numbers of punctuation characters.
b) After the first character, numbers and punctuation characters are allowed.
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XML Rules (cont.)
c) Names cannot contain spaces. d) Names should not contain the ":" character as it is a
"reserved" character. e) Names cannot start with the letters "xml" in any
combination of case. f) The element name must come directly after the "<" without
any spaces between them.
5. XML is case sensitive. 6. XML preserves white space within text. 7. Elements may contain attributes. If an attribute is
present, it must have a value, even if it is an empty string "".
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Spot the error!
<?xml version="1.0" encoding="ISO-8859-1"?>
<note date=12/11/2002>
<to>Tove</to>
<from>Jani</from>
</note>
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Spot the error!
<?xml version="1.0" encoding="ISO-8859-1"?>
<note date="12/11/2002">
<to>Tove</to>
<from>Jani</from>
</note>
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With XML, CR / LF is converted to LF
• Windows: CR + LF
• Unix: LF
• Macintosh: CR
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There is Nothing Special About XML
• plain text w XML tags
• Software that can handle plain text can also handle XML.
• In an XML-aware application, the XML tags can be handled specially: – Visibility,– Functional meaning, etc.
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Is this an error?
<note>
<to>Tove</to>
<from>Jani</from>
<body>Don't forget me this weekend!</body>
</note>
<heading>Reminder</heading>
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XML Elements have Relationships
• Elements are related as parents and children.
• Root element / Parents
• Children / Siblings
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Elements• An element consists of all the information from the
beginning of a start-tag to the end of an end-tag including everything in between.
• E.g. from (X)HTML, all of the following would be the equivalent of one element, named h1:
<h1>This is a heading.</h1> – Where, <h1> is the start tag, </h1> is the end tag, and the
content is in between.
• Each XML document has a root element within which all other elements are nested.
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Examples
• See at:– http://www.intranetjournal.com/articles/200
402/ij_02_10_04a.html– http://prolearn.dcs.warwick.ac.uk/caf/gipfB
egIntAdv.xml– Search more by yourself and familiarize
yourself with the syntax!
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XML Attributes
• XML elements can have attributes.
• From HTML you will remember this: <IMG SRC="computer.gif">
• The SRC attribute provides additional information about the IMG element.
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Attributes versus Elements
• <person sex="female"> <firstname>Anna</firstname> <lastname>Smith</lastname> </person>
• <person> <sex>female</sex> <firstname>Anna</firstname> <lastname>Smith</lastname> </person>
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Comments
• same as in any other languages with line(s) of code whose sole purpose is to provide the developer, and anyone reading the code in the future, information about the code.
<!-- all the comments go in here -->
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XML Validation: Well Formed-ness
• An XML document is well formed, if all the XML rules are obeyed.
(with 7 XML rules as defined in slides 27-28)
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XML declaration
• Every XML document begins with a declaration (not mandatory, good practice)
<?xml version=“1.0”?> • Or, using optional attributes:<?xml version=“1.0” encoding=“UTF-16” standalone=“yes”?>
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Document Type Definition (DTD)
• which tags and attributes are allowed,
• where they can be placed, and
• whether or not they can be nested within a given document.
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Document Type Declaration (DOCTYPE)
• <!DOCTYPE MovieCatalog SYSTEM "movie_catalog.dtd">
Root document element
URL to DTD(external subset via a system identifier)
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Internal vs External DTD declaration
Internal:
<!DOCTYPE foo [ <!ENTITY greeting "hello"> ]>
External, public:
<!DOCTYPE html PUBLIC "//W3C//DTD HTML 4.01//EN” >
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Valid XML Documents
• A "Valid" XML document is a "Well Formed" XML document, which also conforms to the rules of a Document Type Definition (DTD):
<?xml version="1.0" encoding="ISO-8859-1"?>
<!DOCTYPE note SYSTEM "InternalNote.dtd">
<note> <to>Tom</to> <from>Jane</from> <heading>Reminder</heading> <body>Don't forget me this weekend!</body>
</note>
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Validator
• http://xmlvalidator.new-studio.org/
• Also at: http://validator.w3.org/#validate_by_input
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Internal DTD<?xml version="1.0"?> <!DOCTYPE note [ <!ELEMENT note (to,from,heading,body)> <!ELEMENT to (#PCDATA)> <!ELEMENT from (#PCDATA)> <!ELEMENT heading (#PCDATA)> <!ELEMENT body (#PCDATA)> <!ATTLIST body lang CDATA "EN"> ]> <note> <to>Tove</to> <from>Jani</from> <heading>Reminder</heading> <body>Don't forget me this weekend!</body> </note>
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External DTD
<!ELEMENT note (to,from,heading,body)>
<!ELEMENT to (#PCDATA)>
<!ELEMENT from (#PCDATA)>
<!ELEMENT heading (#PCDATA)>
<!ELEMENT body (#PCDATA)>
>> saved as file note.dtd
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XML Schema (XSD)
• XML Schema is an XML based alternative to DTD.
• W3C supports an alternative to DTD called XML Schema:http://www.w3.org/XML/Schema
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Displaying your XML Files with CSS?• It is possible to use CSS to format an XML document.• Example:• XML file: The CD catalog• style sheet: The CSS file• product: The CD catalog formatted with the CSS file• Below is a fraction of the XML file. The second line,
<?xml-stylesheet type="text/css" href="cd_catalog.css"?>, links the XML file to the CSS file
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Displaying XML with XSL
• XSL is the preferred style sheet language of XML.
• XSL (the eXtensible Stylesheet Language) is far more sophisticated than CSS.
• examples:– View the XML file, the XSL style sheet, and
View the result.
<?xml version="1.0" encoding="ISO-8859-1"?> <?xml-stylesheet type="text/xsl" href=“simple.xsl"?>
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XML Conclusions• We have learned:
– XML history– What it is– How it works– Differences to (X)HTML– XML flow– XML Rules– XML Elements, Relationships, Attributes,
Comments– Well-formed-ness concept– XML supporting frame: XML Schema or DTD– Generics on displaying XML
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Why an XML Editor?• XML Schema to define XML structures and data
types • XSLT to transform XML data • SOAP to exchange XML data between applications • WSDL to describe web services • RDF to describe web resources • XPath and XQuery to access XML data • SMIL to define graphics • Altova's XMLSpy
– 30 days free trial– http://www.altova.com/products/xmlspy/xsl_xslt_editor.html
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• Next:– We look at how to access elements and
attributes inside the XML– This can be done via …
– XPATH
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