Indexing
• The syntax for creating a index is:
• CREATE [UNIQUE] INDEX index_name
ON table_name (column1, column2,...
column_n)
[ COMPUTE STATISTICS ];
• Why do we need index?
1
Normalisation
• Normalisation can be considered as a
process for reducing redundancies and
eliminating insertion/deletion/updation
anamolies
• What is wrong with EMP_DEPT?
2
XML
XML material is a modified version
from Dr.Sagiv’s slides
3
XML vs. HTML
• HTML is a HyperText Markup language
– Designed for a specific application,
namely, presenting and linking hypertext
documents
• XML describes structure and content
(“semantics”)
– The presentation is defined separately
from the structure and the content
4
An Address Book as
an XML document
<addresses>
<person>
<name> Donald Duck</name>
<tel> 414-222-1234 </tel>
<email> donald@yahoo.com </email>
</person>
<person>
<name> Miki Mouse</name>
<tel> 123-456-7890 </tel>
<email>miki@yahoo.com</email>
</person>
</addresses>
5
Main Features of XML
• No fixed set of tags
– New tags can be added for new
applications
• An agreed upon set of tags can be used
in many applications
– Namespaces facilitate uniform and
coherent descriptions of data
• For example, a namespace for address books
determines whether to use <tel> or <phone>
6
Main Features of XML (cont’d)
• XML has the concept of a schema
– DTD and the more expressive XML
Schema
• XML is a data model
– Similar to the semistructured data model
• XML supports internationalization
(Unicode) and platform independence
(an XML file is just a character file)
7
XML is the Standard for
Data Exchange
• Web services (e.g., ecommerce) require
exchanging data between various
applications that run on different
platforms
• XML (augmented with namespaces) is
the preferred syntax for data exchange
on the Web
8
XML is not Alone
• XML Schemas strengthen the data-modeling
capabilities of XML (in comparison to XML with
only DTDs)
• XPath is a language for accessing parts of
XML documents
• XLink and XPointer support cross-references
• XSLT is a language for transforming XML
documents into other XML documents
(including XHTML, for displaying XML files)
– Limited styling of XML can be done with CSS alone
• XQuery is a lanaguage for querying XML
documents
9
The Two Facets of XML
• Some XML files are just text documents with
tags that denote their structure and include
some metadata (e.g., an attribute that gives
the name of the person who did the
proofreading)
– See an example on the next slide
– XML is a subset of SGML (Standard Generalized
Markup Language)
• Other XML documents are similar to
database files (e.g., an address book)
10
XML can Describe
the Structure of a Document
• <book year="1994">
<title>TCP/IP Illustrated</title>
<author>
<last>Stevens</last>
<first>W.</first>
</author>
<publisher>Addison-Wesley</publisher>
<price>65.95</price>
</book>
11
XML Syntax
W3Schools Resources on XML Syntax
12
The Structure of XML
• XML consists of tags and text
• Tags come in pairs <date> ... </date>
• They must be properly nested
– good
<date> ... <day> ... </day> ... </date>
– bad
<date> ... <day> ... </date>... </day>
(You can’t do <i> ... <b> ... </i> ...</b> in HTML)
13
A Useful Abbreviation
Abbreviating elements with empty contents:
• <br/> for <br></br>
• <hr width=“10”/> for <hr width=“10”></hr>
For example:
<family>
<person id = “lisa”>
<name> Lisa Simpson </name>
<mother idref = “marge”/>
<father idref = “homer”/>
</person>
...
</family>
Note that a tag
may have a set
of attributes,
each consisting
of a name and
a value
14
XML Text
XML has only one “basic” type – text
It is bounded by tags, e.g.,
<title> The Big Sleep </title>
<year> 1935 </ year> – 1935 is still text
• XML text is called PCDATA
– (for parsed character data)
• It uses a 16-bit encoding, e.g., \&\#x0152 for
the Hebrew letter Mem
15
XML Structure
• Nesting tags can be used to express
various structures, e.g., a tuple
(record):
<person>
<name> Lisa Simpson</name>
<tel> 02-828-1234 </tel>
<tel> 054-470-777 </tel>
<email> lisa@cs.huji.ac.il </email>
</person>
16
XML Structure (cont’d)
• We can represent a list by using the
same tag repeatedly:
<addresses>
<person> … </person>
<person> … </person>
<person> … </person>
<person> … </person>
…
</addresses>
17
XML Structure (cont’d)
<addresses>
<person>
<name> Donald Duck</name>
<tel> 04-828-1345 </tel>
<email> donald@cs.technion.ac.il </email>
</person>
<person>
<name> Miki Mouse</name>
<tel> 03-426-1142 </tel>
<email>miki@yahoo.com</email>
</person>
</addresses>
18
Terminology
The segment of an XML document
between an opening and a corresponding
closing tag is called an element
element
element,
a sub-element of
<person>
<name> Bart Simpson </name>
<tel> 02 – 444 7777 </tel>
<tel> 051 – 011 022 </tel>
<email> bart@tau.ac.il </email>
</person>
not an element
19
An XML Document is a Tree
person
name
tel
tel
email
Bart Simpson
051 – 011 022
02 – 444 7777
bart@tau.ac.il
Leaves are either empty or contain PCDATA
20
Mixed Content
An element may contain a mixture of subelements and PCDATA
<airline>
<name> British Airways </name>
<motto>
World’s <dubious> favorite</dubious>
airline
</motto>
</airline>
21
The Header Tag
• <?xml version="1.0" standalone="yes/no"
encoding="UTF-8"?>
– Standalone=“no” means that there is an
external DTD
– You can leave out the encoding attribute and
the processor will use the UTF-8 default
22
Processing Instructions
<?xml version="1.0"?>
<?xml-stylesheet href="doc.xsl" type="text/xsl"?>
<!DOCTYPE doc SYSTEM "doc.dtd">
<doc>Hello, world!<!-- Comment 1 --></doc>
<?pi-without-data?>
<!-- Comment 2 -->
<!-- Comment 3 -->
23
Using CDATA
<HEAD1>
Entering a Kennel Club Member
</HEAD1>
We want to see
the text as is,
even though
it includes tags
<DESCRIPTION>
Enter the member by the name on his or her papers. Use the
NAME tag. The NAME tag has two attributes. Common (all in
lowercase, please!) is the dog's call name. Breed (also in all
lowercase) is the dog's breed. Please see the breed reference
guide for acceptable breeds. Your entry should look something
like this:
</DESCRIPTION>
<EXAMPLE>
<![CDATA[<NAME common="freddy" breed"=springerspaniel">Sir Fredrick of Ledyard's End</NAME>]]>
</EXAMPLE>
24
Well-Formed XML Documents
• An XML document (with or without a DTD) is
well-formed if
– Tags are syntactically correct
– Every tag has an end tag
– Tags are properly nested
– There is a root tag
An XML document
must be well formed
– A start tag does not have two occurrences of the
same attribute
25
Representing relational
databases
A relational database for school:
student:
course:
id
name
gpa
001
002
…
Joe
Mary
…
3.0
4.0
…
enroll:
id
cno
001
001
002
…
331
350
331
…
cno
title
credit
331
350
…
DB
Web
…
3.0
3.0
…
26
XML representation
<school>
<student id=“001”>
<name> Joe </name>
<gpa>
3.0 </gpa>
</student>
<student id=“002”>
<name> Mary </name>
<gpa>
4.0 </gpa>
</student>
<course cno=“331”>
<title> DB </title>
<credit>
3.0 </credit>
<credit>
3.0 </credit>
</course>
<course cno=“350”>
<title> Web </title>
</course>
27
XML representation
<enroll>
<id> 001 </id>
</enroll>
<enroll>
<id> 001 </id>
</enroll>
<enroll>
<id> 002 </id>
</enroll>
</school>
<cno>
331 </cno>
<cno>
350 </cno>
<cno>
331 </cno>
28