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Part I: Background
• What’s the difference between– The world of documents and
information retrieval, and – Databases and query interfaces?
3
Documents vs. DatabasesDocument World• Plenty of small
documents• Usually static • Implicit structure:
section, paragraph,table of contents
• Tagging
Database World• A few large
databases• Usually dynamic• Explicit
structure: schema
• Records
4
Documents vs. Databases (cont’d)
Document World• Human friendly• Content:
form/layout,annotation
• Paradigms:“Save as”,Wysiwyg
• Meta-data:author name,date, subject
Database World• Machine friendly• Content:
schema, data,methods
• Paradigms:Atomicity, Concurrency,Isolation, Durability
• Meta-data:schema description
5
What can be Done with Them
Documents Database
editing
printing
spell-checkingcounting
words retrieving (IR)
searching
updating
clustering
cleaning
querying
adjusting
transforming
6
HTML• Hypertext Markup Language• Used for publishing hypertext on
the World-Wide Web• Designed to describe how a Web
browser should arrange text, images and push-buttons on a page
• Easy to learn, but does not convey structure
• Fixed tag set
7
HTML Example
<HTML><HEAD><TITLE>Welcome to the DBI course</TITLE></HEAD><BODY>
<H1>Introduction</H1><IMG SRC= "dragon.gif" WIDTH="200" HEIGHT="150" >
</BODY></HTML>
Opening tagText (PCDATA)
Closing tag
“Bachelor” tag
Attribute name Attribute value
Opening tagText (PCDATA)
Closing tagAttribute name Attribute value
“Bachelor” tag
8
HTML
• The World-Wide Web is constructed from HTML documents
• We can apply information-retrieval techniques to a set of documents– For example, clustering as Google
does
• How can we apply database techniques to the Web?
9
HTML Pages
• We can– Edit (and put on the Web)– Print (or view with a browser)– Spell-check– Count words– Retrieve (again, with a browser)– Search (with a search engine, for
example)– Cluster
10
How can we Ask Queries?• How can we find automatically the
cheapest flight from Israel to Micronezia, knowing the Web sites of all airlines that have flights to Micronezia?
• How can we find automatically the phone numbers of people that advertised on the Web that they want to sell a car for a price that is not greater than 30,000 IS?
• It can be useful to query data as we do in databases
11
Thin Red Line
• The line between the document world and the database world is not clear
• In some cases, both approaches are legitimate
• An interesting middle ground is data formats – of which XML is an example
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
XML TextXML 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
14
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>
15
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>
16
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>
17
TerminologyThe segment of an XML document between an opening and a corresponding closing tag is called an element
<person> <name> Bart Simpson </name>
<tel> 02 – 444 7777 </tel> <tel> 051 – 011 022 </tel>
<email> bart@tau.ac.il </email> </person>
element
element, a sub-element of
not an element
18
XML Document is a Tree
person
name emailtel tel
Bart Simpson
02 – 444 7777
051 – 011 022
bart@tau.ac.il
Semistructured data models typically put the labels on the edges
19
Mixed Content
An element may contain a mixture of sub-elements and PCDATA
<airline> <name> British Airways </name> <motto> World’s <dubious> favorite</dubious>
airline </motto></airline>
20
Needs for Mixed Content• Mixed-content data is not typically
generated from databases • It is needed for consistency with HTML• For example:
<html><head></head><body>
Why can’t you find <it>dragons</it> in a restaurant?
Because <b>smoking</b> is not allowed</body>
</html>
21
A Complete XML Document<?XML version ="1.0" encoding="UTF-8" standalone="no"?><!DOCTYPE addresses SYSTEM "http://www.cs.huji.ac.il/~dbi/dbi-addresses.dtd"><addresses>
<person><name>Lisa Simpson</name><tel> 02-828-1234 </tel><tel> 054-470-777 </tel><email> lisa@cs.huji.ac.il </email>
</person></addresses>
22
The Header Tag
• <?xml version="1.0“ standalone="yes/no" encoding="UTF-8"?>
• You can leave out the encoding attribute and the processor will use the UTF-8 default
23
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 -->
24
Two Ways of Representing a Relational Database in XML
projects:title budget managedBy
employees:
name ssn age
25
Project and Employee relations in XML
<db> <project> <title> Pattern recognition
</title> <budget> 10000
</budget> <managedBy> Joe
</managedBy> </project> <employee> <name> Joe </name> <ssn> 344556 </ssn> <age> 34 < /age> </employee>
<employee> <name> Sandra </name> <ssn> 2234 </ssn> <age> 35 </age> </employee> <project> <title> Auto guided vehicle
</title> <budget> 70000 </budget> <managedBy> Sandra </managedBy> </project> :</db>
Projects and employees are intermixed
26
<db> <projects> <project> <title> Pattern recognition </title> <budget> 10000 </budget> <managedBy> Joe</managedBy> </project> <project> <title> Auto guided vehicles </title> <budget> 70000 </budget>
<managedBy>Sandra</managedBy>
</project> : </projects>
<employees><employee>
<name> Joe </name>
<ssn> 344556 </ssn>
<age> 34 </age> </employee> <employee>
<name>Sandra</name> <ssn> 2234 </ssn>
<age>35 </age> </employee> : <employees></db>
Employees follow projects
Projects
Employees
27
<db> <projects> <title> Pattern recognition
</title> <budget> 10000 </budget> <managedBy> Joe
</managedBy> <title> Auto guided vehicles
</title> <budget> 70000 </budget> <managedBy> Sandra
</managedBy> : </projects>
<employees> <name> Joe </name> <ssn> 344556 </ssn> <age> 34 </age> <name> Sandra </name> <ssn> 2234 </ssn> <age> 35 </age> : </employees></db>
Or without “separator” tags …
Can be done if it is clearwhere each employeeand each project starts
28
Attributes• An (opening) tag may contain attributes • These are typically used to describe the contents of an element
<entry> <word language = “en”> cheese</word> <word language = “fr”> fromage</word> <word language = “ro”> branza </word> <meaning> A food made … </meaning></entry>
29
Attributes (cont’d)
Another common use for attributes is to express dimension or type
<picture> <height dim= “cm”> 2400 </height> <width dim= “in”> 96 </width> <data encoding = “gif” compression = “zip”> M05-.+C$@02!G96YE<FEC ... </data></picture>
30
Well-Formed Documents
A document that – obeys the “nested-tags” rule,
and – does not repeat an attribute
within a tag
is said to be well-formed
31
<addresses ><person friend="yes">
<name> Jeff Cohen</name><tel> 04-828-1345 </tel><tel> 054-470-778 </tel><email> jeffc@cs.technion.ac.il </email>
</person><person friend="no">
<name> Irma Levy</name><tel> 03-426-1142 </tel><email>irmal@yourmail.com</email>
</person></addresses>
UsingAttributes
32
When to Use Attributes
• It’s not always clear when to use attributes
<person ssno= “123 4589”> <name> L. Simpson
</name> <email> lisa@cs.huji.ac.il </email> ...</person>
<person> <ssno> 123 4589 </ssno> <name> L. Simpson </name> <email> lisa@cs.huji.ac.il </email> ...</person>
33
Using IDs<person id="jeff" friend="yes" knows="irma">
<name> Jeff Cohen</name><tel> 04-828-1345 </tel><tel> 054-470-778 </tel><email> jeffc@cs.technion.ac.il </email>
</person><person id="irma" friend="no" knows="jeff">
<name> Irma Levy</name><tel> 03-426-1142 </tel><email>irmal@yourmail.com</email>
</person>
IDattributes
34
Using IDs<family> <person id=“lisa” mother=“marge” father=“homer”> <name> Lisa Simpson </name> </person>
<person id=“bart” mother=“marge” father=“homer”> <name> Bart Simpson </name> </person> <person id=“marge” children=“bart lisa”> <name> Marge Simpson </name> </person> <person id=“homer” children=“bart lisa”> <name> Homer Simpson </name> </person></family>
35
ODL Schema
class Movie
( extent Movies, key title )
{
attribute string title;
attribute string director;
relationship set<Actor> casts
inverse Actor::acted_In;
attribute int budget;
} ;
class Actor
( extent Actors, key name )
{
attribute string name;
relationship set<Movie> acted_In
inverse Movie::casts;
attribute int age;
attribute set<string> directed;
} ;
36
<db> <movie id=“m1”> <title>Waking Ned
Divine</title> <director>Kirk Jones
III</director> <cast idrefs=“a1
a3”></cast> <budget>100,000</budget>
</movie> <movie id=“m2”> <title>Dragonheart</title> <director>Rob
Cohen</director> <cast idrefs=“a2 a9
a21”></cast> <budget>110,000</budget>
</movie> <movie id=“m3”> <title>Moondance</title> <director>Dagmar
Hirtz</director> <cast idrefs=“a1
a8”></cast> <budget>90,000</budget> </movie> :
class Movie
( extent Movies, key title )
{
attribute string title;
attribute string director;
relationship set<Actor> casts
inverse Actor::acted_In;
attribute int budget;
} ;
37
class Actor
( extent Actors, key name )
{
attribute string name;
relationship set<Movie> acted_In
inverse Movie::casts;
attribute int age;
attribute set<string> directed;
} ;
<db> : <actor id=“a1”> <name>David Kelly</name> <acted_In idrefs=“m1 m3 m78” > </acted_In> </actor> <actor id=“a2”> <name>Sean Connery</name> <acted_In idrefs=“m2 m9 m11”> </acted_In> <age>68</age> </actor> <actor id=“a3”> <name>Ian Bannen</name> <acted_In idrefs=“m1 m35”> </acted_In> </actor> :</db>
38
<db> <movie id=“m1”> <title>Waking Ned
Divine</title> <director>Kirk Jones
III</director> <cast idrefs=“a1
a3”></cast> <budget>100,000</budget>
</movie> <movie id=“m2”> <title>Dragonheart</title> <director>Rob
Cohen</director> <cast idrefs=“a2 a9
a21”></cast> <budget>110,000</budget>
</movie> <movie id=“m3”> <title>Moondance</title> <director>Dagmar
Hirtz</director> <cast idrefs=“a1
a8”></cast> <budget>90,000</budget> </movie> :
<actor id=“a1”> <name>David Kelly</name> <acted_In idrefs=“m1 m3 m78” > </acted_In> </actor> <actor id=“a2”> <name>Sean Connery</name> <acted_In idrefs=“m2 m9 m11”> </acted_In> <age>68</age> </actor> <actor id=“a3”> <name>Ian Bannen</name> <acted_In idrefs=“m1 m35”> </acted_In> </actor> :</db>
40
Document Type Descriptors
• Document Type Descriptors (DTDs) impose structure on an XML document
• There is some relationship between a DTD and a schema, but it is not close – hence the need for additional “typing” systems (XML schemas)
• The DTD is a syntactic specification
41
Example: An Address Book<person>
<name> Homer Simpson </name>
<greet> Dr. H. Simpson </greet>
<addr>1234 Springwater Road </addr>
<addr> Springfield USA, 98765 </addr>
<tel> (321) 786 2543 </tel>
<fax> (321) 786 2544 </fax>
<tel> (321) 786 2544 </tel>
<email> homer@math.springfield.edu </email>
</person>
Mixed telephones and faxes
As manyas needed
As many address lines as needed (in order)
At most one greeting
Exactly one name
42
Specifying the Structure
• name to specify a name element
• greet? to specify an optional (0 or 1) greet
elements
• name, greet? to specify a name followed by an optional greet
43
Specifying the Structure (cont’d)
• addr* to specify 0 or more address lines
• tel | fax a tel or a fax element
• (tel | fax)* 0 or more repeats of tel or fax
• email* 0 or more email elements
44
Specifying the Structure (cont’d)
• So the whole structure of a person entry is specified by
name, greet?, addr*, (tel | fax)*, email*
• This is known as a regular expression
• Why is it important?
45
Regular Expressions
• Each regular expression determines a corresponding finite state automaton• Let’s start with a simpler example:
name, addr*, emailname
addr
This suggests a simple parsing program
46
Another Example
name,address*,(tel | fax)*,email*
name
address
tel
tel
fax
fax
Adding in the optional greet furthercomplicates things
47
Internal DTD For the Address Book
<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE addressbook [ <!ELEMENT addressbook (person*)> <!ELEMENT person (name, greet?, address*, (fax | tel)*, email*)> <!ELEMENT name (#PCDATA)> <!ELEMENT greet (#PCDATA)> <!ELEMENT address(#PCDATA)> <!ELEMENT tel (#PCDATA)> <!ELEMENT fax (#PCDATA)> <!ELEMENT email (#PCDATA)>]>
The name ofthe DTD is
addressbook
“Internal” means that the DTD and theXML Document are in the same file
48
Rest of the Address Book
<addressbook> <person> <name> Jeff Cohen </name> <greet> Dr. Cohen </greet>
<email> jc@penny.com </email> </person></addressbook>
50
Two DTDs for the Relational DB
<!DOCTYPE db [<!ELEMENT db (projects,employees)><!ELEMENT projects (project*)><!ELEMENT employees (employee*)>
<!ELEMENT project (title, budget, managedBy)>
<!ELEMENT employee (name, ssn, age)>...
]><!DOCTYPE db [
<!ELEMENT db (project | employee)*><!ELEMENT project (title, budget,
managedBy)><!ELEMENT employee (name, ssn, age)>...]>
51
Recursive DTDs
<DOCTYPE genealogy [<!ELEMENT genealogy (person*)><!ELEMENT person (name,dateOfBirth,person, -- motherperson )> -- father ...
]>
What is the problem with this?A parser does not notice it!
Each person should have a father and amother. Thisleads to eitherinfinite data ora person thatis a descendentof himself.
52
Recursive DTDs (cont’d)
<DOCTYPE genealogy [<!ELEMENT genealogy (person*)><!ELEMENT person (
name,dateOfBirth,person?, -- motherperson? )> -- father
... ]>
What is now the problem with this?
If a person hasonly a father, how can you tell that he has a father anddoes not havea mother?
53
Some Things are Hard to Specify
Each employee element is to contain name, age and ssn elements in some order
<!ELEMENT employee ( (name, age, ssn) | (age, ssn, name) |
(ssn, name, age) | ... )>
Suppose there were many more fields!
54
Some Things are Hard to Specify (cont’d)
<!ELEMENT employee ( (name, age, ssn) | (age, ssn, name) |
(ssn, name, age) | ... )>
Suppose there were many more fields!
There are n! differentorders of n elements
It is not even polynomial
55
General Definitions of Entities
ANY - tells that the element can have any
content
EMPTY - tells that the element has nocontent
56
Summary of XML regular expressions
• A The tag A occurs• e1,e2 The expression e1 followed
by e2• e* 0 or more occurrences of e• e? Optional – 0 or 1 occurrences• e+ 1 or more occurrences• e1 | e2 either e1 or e2• (e) grouping
57
Deterministic Requirement• If element-type declarations are
deterministic, it is easier• Formally, the Glushkov automaton
is deterministic• The states of this automaton are
the positions of the regular expression (semantic actions)
• The transitions are based on the “follows set”
58
Deterministic Requirement (cont’d)
• The associated automata are succinct
• A regular language may not have an associated deterministic grammar, e.g., <!ELEMENT ndeter
((movie|director)*,movie,(movie|director))>
59
Specifying Attributes in the DTD
<!ELEMENT height (#PCDATA)><!ATTLIST height dimension CDATA #REQUIRED accuracy CDATA #IMPLIED >
The dimension attribute is required The accuracy attribute is optional
CDATA is the “type” of the attribute – it means string, and may take any literal string as a value
60
Specifying ID and IDREF Attributes
<!DOCTYPE family [ <!ELEMENT family (person)*> <!ELEMENT person (name)> <!ELEMENT name (#PCDATA)> <!ATTLIST person
id ID #REQUIRED mother IDREF #IMPLIED father IDREF #IMPLIED children IDREFS #IMPLIED>]>
61
Specifying ID and IDREF Attributes (cont’d)
• The attributes mother and father are references to IDs of other elements
• However, those are not necessarily person elements!
• The mother attribute is not necessarily a reference to a female personReferences to IDs
have no type
62
Some Conforming Data<family> <person id=“lisa” mother=“marge” father=“homer”> <name> Lisa Simpson </name> </person>
<person id=“bart” mother=“marge” father=“homer”> <name> Bart Simpson </name> </person> <person id=“marge” children=“bart lisa”> <name> Marge Simpson </name> </person> <person id=“homer” children=“bart lisa”> <name> Homer Simpson </name> </person></family>
63
Consistency of ID and IDREF Attribute Values
•If an attribute is declared as ID– the associated values must all be distinct (no
confusion)
•If an attribute is declared as IDREF– the associated value must exist as the value
of some ID attribute (no dangling “pointers”)
•Similarly for all the values of an IDREFS attribute
•ID and IDREF attributes are not typed
64
A Useful AbbreviationWhen an element has empty content we can use• <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>
65
An Alternative Specification <?xml version="1.0" encoding="UTF-8"?><!DOCTYPE family [
<!ELEMENT family (person)*><!ELEMENT person (name, mother?, father?, children?)><!ATTLIST person id ID #REQUIRED><!ELEMENT name (#PCDATA)><!ELEMENT mother EMPTY><!ATTLIST mother idref IDREF #REQUIRED><!ELEMENT father EMPTY><!ATTLIST father idref IDREF #REQUIRED><!ELEMENT children EMPTY><!ATTLIST children idrefs IDREFS #REQUIRED>
]>
66
The Revised Data<family>
<person id=“marge"> <name> Marge Simpson </name> <children idrefs=“bart lisa"/>
</person><person id=“homer"> <name> Homer Simpson </name> <children idrefs=“bart lisa"/></person>
<person id=“bart"> <name> Bart
Simpson </name> <mother idref=“marge"/> <father idref=“homer"/>
</person><person id=“lisa"> <name> Lisa Simpson </name></person>
</family>
67
ODL Schema
class Movie
( extent Movies, key title )
{
attribute string title;
attribute string director;
relationship set<Actor> cast
inverse Actor::acted_In;
attribute int budget;
} ;
class Actor
( extent Actors, key name )
{
attribute string name;
relationship set<Movie>
acted_In
inverse Movie::cast;
attribute int age;
attribute set<string> directed;
} ;
68
Schema.dtd
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE db [ <!ELEMENT db (movie+, actor+)> <!ELEMENT movie
(title,director,cast,budget)> <!ATTLIST movie id ID #REQUIRED> <!ELEMENT title (#PCDATA)> <!ELEMENT director (#PCDATA)> <!ELEMENT cast EMPTY> <!ATTLIST cast idrefs IDREFS #REQUIRED> <!ELEMENT budget (#PCDATA)>
The DTD continues in the next slide
69
Schema.dtd (cont’d)
<!ELEMENT actor (name, acted_In,age?, directed*)>
<!ATTLIST actor id ID #REQUIRED> <!ELEMENT name (#PCDATA)> <!ELEMENT acted_In EMPTY> <!ATTLIST acted_In idrefs IDREFS
#REQUIRED> <!ELEMENT age (#PCDATA)> <!ELEMENT directed (#PCDATA)>]>
70
Data <db> <movie id="ohgod"> <title> Oh God!</title> <director> Woody Allen </director> <cast idrefs="burns"></cast> <budget> $2M </budget> </movie> <actor id="burns"> <name> George Burns </name> <acted_In idrefs="ohgod" /> </actor></db>
71
Constraints on IDs and IDREFs
• ID stands for identifier
– No two ID attributes may have the same value (of type CDATA)
• IDREF stands for identifier reference
– Every value associated with an IDREF attribute must exist as an ID attribute value
• IDREFS specifies several (0 or more) identifiers
72
Adding a DTD to the Document• A DTD can be internal
– The DTD is part of the document file
• or external– The DTD and the document are on
separate files– An external DTD may reside
•In the local file system (where the document is)
•In a remote file system
73
Connecting a Document with its DTD
• An internal DTD:<?xml version="1.0"?>
<!DOCTYPE db [<!ELEMENT ...> … ]><db> ... </db>
• A DTD from the local file system: <!DOCTYPE db SYSTEM "schema.dtd">
• A DTD from a remote file system: <!DOCTYPE db SYSTEM "http://www.schemaauthority.com/schema.dtd">
74
Well-formed and Valid Documents
• A document (with or without a DTD) is well-formed if it has– proper nesting of tags and unique attributes
• A valid document conforms to the DTD, i.e.,– the document conforms to the regular-
expression grammar,
– types of attributes are correct, and
– constraints on references are satisfied
75
DTDs vs. Schemas (or Types)• DTDs are rather weak specifications by DB
& programming-language standards– Only one base type – PCDATA– No useful “abstractions”, e.g., sets– IDREFs are untyped – the type of the object
being referenced is not known– No constraints, e.g., child is inverse of parent– No methods– Tag definitions are global
• Some extensions of XML impose a schema or types on an XML document
We may see these later
77
What are Entities?
• An entity is a shortcut to a set of information
• You might think of an entity as being a bit like a macro
• Entities allow dividing a document between some different storage devices
78
Why to Use Entities
• Entities allow sharing data between documents
• Entities save typing• Entities can reduce errors • Entities are easy to update• Entities can act as placeholders for
TBD (to be determined) information
79
Defining Entities• Entities can be defined
– in the local document as part of the DOCTYPE definition
– with a link to external files that contain the entity data (this, too, is done through the DOCTYPE definition)
– in an external DTD
• Define locally when the entity is being used only in one particular document
• Define by a link to an external file when the entity is being used in many documents
80
Kinds of Entities
There are two kinds of entities:• General entities
– For usage in documents
• Parameter entities– For usage in declarations
81
General entities
• The definition of a general entitiy in the DTD
<!ENTITY Name EntityDefinition >
• The usage of the entity in the document is by
&Name;
82
Example<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE mdb [
<!ENTITY bm "bad movie"> <!ELEMENT mdb (movie+)>
<!ELEMENT movie (title,director,cast?,budget)>]><mdb>
<movie id="ohgod" opinion="&bm;"><title> Oh God!</title><director> Woody Allen </director><budget> $2M </budget>
</movie></mdb>
84
Unparsed Entities<!DOCTYPE mdb [
<!NOTATION gif SYSTEM "c:\Program Files\Netscape\Communicator\Program\Netscape.exe"><!ENTITY starpicture SYSTEM "http://www.cs.huji.ac.il/~dbi/figures/star.gif" NDATA gif><!ENTITY bm "bad movie"><!ELEMENT mdb (movie+)><!ELEMENT movie (title,director, budget)><!ATTLIST movie id ID #REQUIRED
opinion CDATA #IMPLIED starimage ENTITY #IMPLIED>
<!ELEMENT title (#PCDATA)><!ELEMENT director (#PCDATA)><!ELEMENT budget (#PCDATA)>
]>Entities are defined
Types are
defined
85
Data
<mdb>
<movie id="ohgod" opinion="&bm;" starimage="starpicture">
<title> Oh God!</title>
<director> Woody Allen </director>
<budget> $2M </budget>
</movie>
</mdb>
86
Parameter Entities• Parameter entities are used only within DTDs• They carry information for use in the markup
declaration
– Internal entities - references are within the DTD
– External entities - references draw information
from outside files
• Parameter Entity declaration:<!ENTITY % Name EntityDefinition >
87
Parameter Entity Example<?xml version="1.0" encoding="UTF-8"?><!ENTITY % essential "name, tel*"><!ELEMENT email (#PCDATA)><!ELEMENT tel (#PCDATA)><!ELEMENT name (#PCDATA)><!ELEMENT person (%essential;, email, advisor?)><!ATTLIST person friend (yes | no) #IMPLIED id ID #REQUIRED knows IDREFS #IMPLIED><!ELEMENT advisor (person)><!ELEMENT addresses (person)*>
88
Defining Entities• Local Definition:
<!DOCTYPE [ <!ENTITY copyright
"Copyright 2000, As The World Spins Corp. All
rights reserved. Please do not copy or use without
authorization. For authorization contact
legal@worldspins.com."> ]>
• Global Definition:<!DOCTYPE [ <!ENTITY copyright SYSTEM
"http://www.worldspins.com/legal/copyright.xml"> ]>
89
Example<?xml version="1.0"><!DOCTYPE [ <!ENTITY copyright "Copyright 2000, As The World Spins Corp. All
rights reserved. Please do not copy or use without authorization. For authorization contactlegal@worldspins.com.">
<!ENTITY trademark SYSTEM "http://www.worldspins.com/legal/trademark.xml">
]>
90
Example (cont’d)<PRESSRELEASE><HEAD>Mini-globe revolutionizes keychain industry
</HEAD><LEAD>Today As The World Spins introduces a new approach to keychains. With the new MINI-GLOBE keys can be kept inside achain, called for upon demand, and stored safely. Never
more will consumers lose a key or stand at a door flipping through a stack of keys seeking the right one.
</LEAD><LEGAL>&trademark;©right;</LEGAL></PRESSRELEASE>
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Name Spaces
• Namespaces are standard DTDs
• More than one namespace can be used in the same XML document– Different elements of a given
document may conform to different namespaces
• Declaring the namespaces– Each namespace is identified by a URI
92
Example• Defining the used namespace
<document xmlns:dbi= 'http://www.cs.huji.ac.il/dbi-schema'>
• Using a tag from the namespace<dbi:A>This is a text of an element A
according to dbi’s definition</A>
• Using a tag not from the namespace<A>This will probably be understood as an
anchor</A>
96
<?XMLversion ="1.0" encoding="UTF-8" standalone="no"?>
<container xmlns:bi="www.cs.technion.ac.il/~oshmu/container.dtd"> <bi:bdb xmlns:bi="www.cs.technion.ac.il/~oshmu/nss.dtd"> <bi:book>
<title> Godzila</title><author>Jeff Cohen </author>
</bi:book><bk:book xmlns:bk="www.cs.technion.ac.il/~oshmu/namespaces.dtd">
<title>A Suitable Boy</title><price currency="US Dollar">22.95</price>
</bk:book> </bi:bdb></container>
97
Using CDATA<HEAD1>
Entering a Kennel Club Member
</HEAD1>
<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"=springer-spaniel">Sir Fredrick of Ledyard's End</NAME>]]>
</EXAMPLE>
We want to seethe text as is,even though
it includes tags
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Summary• XML is a new data format. Its main virtues:
– widespread acceptance – the (important) ability to handle
semistructured data (data without schema)
• DTDs provide some useful syntactic constraints on documents. As schemas they are weak
• How to store large XML documents?• How to query them?• How to map between XML and other
representations?
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