Basic Technologies - (Unicode, URIs, Namespaces, XML)

Basic Technologies(Unicode, URIs, Namespaces, XML)

Camilo Thorne

Room 00.012Institut fur Maschinelle Sprachverarbeitung

Universitat Stuttgart+49 (0) 711 685-81369

[email protected]

Semantic Web, SS 2017(based on slides by W. Kessler)

C. Thorne (IMS Stuttgart) Basic Technologies SemWeb, SS 2017 1 / 35

[email protected]

The Semantic Web Stack [W3C, Tim Berners-Lee]

URI Unicode, UTF-8

XML, XMLSchema, Namespaces

RDF

SPARQLRDFS

Ontology, OWL

Logic, Rules

Proof

En

cryp

tion

Dig

ital

Sig

nat

ure

s

Trust

User Interface, Software Agents


Outline

1 Recap

2 Unicode: One Character Set to Represent Them All

3 URIs: Unique Resource Identifiers

4 XML: eXtensible Markup Language

5 XML Namespaces

6 XML Schema: Defining XML in XML

7 Summary

8 References


Outline

1 Recap




5 XML Namespaces


7 Summary

8 References


Recap on Modeling Basics

Pinpoint entities, concepts, relations, states of affairs and constraintsmentioned in the following text, and build a formal representation:

Frames were proposed by Marvin Minsky in the paper “A Frame-work for Representing Knowledge.” Frames consist of slots andvalues. Frames are the primary data structure used in AI framelanguages. Frames are similar to class hierarchies in object-oriented languages, but their design goals are different.


Outline

1 Recap




5 XML Namespaces


7 Summary

8 References


Unicode

First computers only “spoke” English and stored the characters with 7bit, the first bit of a byte is 0→ ASCII: A is 01000001

With the first bit set to 1, we can encode “other” stuff→ e.g., in Latin-1: A is 01000001, a is 11100100

You have to know the encoding to display a text correctly which isoften not specified anywhere – this is madness!

Since 1987, there have been attempts to create one character set forevery existing writing system

In 1991 the first Unicode standard was published

Unicode maps each character to a (abstract, hexadecimal) codepoint: A is U+0041, a is U+00E4


UTF-8: An Encoding for Unicode

The way to store a character in bits/bytes is not part of the Unicodestandard

There are many encodings for Unicode, the most widely used isUTF-8

UTF-8 is a variable length encoding and stores Unicode code pointsin one or up to six bytes (up to 6× 8 = 48 bits)

Code points 0-127 are stored in one byte, so that text using onlyEnglish characters looks the same in ASCII and UTF-8

B Examples:

Character Unicode UTF-8

A U+0041 01000001

a U+00E4 11000011 10100100

e U+20AC 11100010 10000010 10101100


UTF-8: An Encoding for Unicode

The way to store a character in bits/bytes is not part of the Unicodestandard

There are many encodings for Unicode, the most widely used isUTF-8

UTF-8 is a variable length encoding and stores Unicode code pointsin one or up to six bytes (up to 6× 8 = 48 bits)

Code points 0-127 are stored in one byte, so that text using onlyEnglish characters looks the same in ASCII and UTF-8

B Examples:

Character Unicode UTF-8

A U+0041 01000001

a U+00E4 11000011 10100100

e U+20AC 11100010 10000010 10101100


Quiz: Unicode

Which of these statements are true?

A) Unicode is an encoding

B) UTF-8 is an encoding

C) One character uses at most 2 byte in UTF-8 encoding

D) There are Unicode code points for Egyptian Hieroglyphs

E) Everybody uses UTF-8 encoding per default today

F) Documents you hand in during this course should use UTF-8


Outline

1 Recap




5 XML Namespaces


7 Summary

8 References


Unique Resource Identifiers (URIs)

“Everything has a URI”

The URI is a unique identifier for a specific resource, i.e., no tworesources can have the same URI in the same domain

One resource can have several URIs, e.g., I have a URI that refers tome as a teacher and one that refers to me as a singer

A URI could be anything, it can be a URL (Unified Resource Locator,or Web address), but not all URIs are URLs

A URI does not necessarily enable access to a resource


URI Examples

For us, URIs will always look like URLs, e.g.,http://www.example.org/#JohnSmith.

URIs have two parts:

Namespace http://www.example.org/#

Local name JohnSmith

We can define prefixes for namespaces and abbreviate URIs withprefix:LocalName.

We will define ex as prefix for the example namespace, sohttp://www.example.org/#JohnSmith is abbreviated asex:JohnSmith


Quiz: URIs

Which of these statements are true?

A) Two different URIs can never refer to the same object.

B) Two different objects can have the same URI.

C) All URIs are URLs.

D) INwOXOz96UQOU is a valid URI.

E) URIs must be assigned by the W3C to be valid.


INwOXOz96UQOU

Outline

1 Recap




5 XML Namespaces


7 Summary

8 References


XML: eXtensible Markup Language

W3C Recommendation since 1998 (first draft 1996).

Markup-language based on tags.

XML separates content from formatting.

XML documents are meant to be understood by bothhumans and computers.

XML as a format for exchanging data became far more common thanoriginally intended.


XML vs. HTML

Both are markup-languages based on tags.

In both languages tags may be nested.

In XML all tags must be closed(every opening tag <tag> must have a closing tag </tag>).HTML allows tags that are not closed.

In XML users define their own tags,HTML has predefined tags.

XML separates content from formatting,HTML does not.


XML Syntax – Prologue and Root Element

<?xml version="1.0" encoding="UTF-8"?>

<pets>

...

</pets>

The first line in any XML file is the XML declaration and specifiesXML version and character encoding.

There is only one outermost element in the document(called the root element).


XML Syntax – Elements

<pet>

<name>Fifi</name>

<petType>Dog</petType>

<dateOfBirth></dateOfBirth>

</pet>

Elements represent the “things” the document talks about.

An element consists of an opening tag with its name, a closing tagand the element’s content between the tags.

The content may be text, other elements, or nothing.

If there is no content, then the element is called empty and can beabbreviated like this: <dateOfBirth />.


XML Syntax – Example


<pets>



<pet>

<name>Fifi</name>



<owner>

<name>Jane Doe</name>

<city>Heretown</city>

</owner>

</pet>

</pets>


XML as a Tree


<pets>


<pet>

<name>Fifi</name>



<owner>



</owner>

</pet>

<pet>

<name>Fluffy</name>

...

</pet

</pets>

pets

pet

name: FifipetType: DogdateOfBirth: –owner

name: Jane Doecity: Heretown

pet

name: Fluffy. . .

. . .


XML as a Tree


<pets>


<pet>

<name>Fifi</name>



<owner>



</owner>

</pet>

<pet>

<name>Fluffy</name>

...

</pet

</pets>

pets

pet

name: FifipetType: DogdateOfBirth: –owner

name: Jane Doecity: Heretown

pet

name: Fluffy. . .

. . .


Quiz: XML

Find the errors in this XML document:


<fruits>

<fruit>

<fruit name>Orange</fruit name>

<price>3.15</pricePerKilo>

<amount>0.570<amount/>

<priceTotal>1.57</priceTotal>

<origin>Germany<producer>Bioland Mauck</origin></producer>

</fruit>

</fruits>

<customer>

<name>John</name><name>Smith</name>

<customerid>7271</customerID>

</customer>


Outline

1 Recap




5 XML Namespaces


7 Summary

8 References


Combining XML Documents

Doc 1 describes books, <title> refers to booktitle:

<book>

<title>Max und Moritz</title>

<author>Wilhelm Busch</author>

</book>

Doc 2 describes people, <title> refers to academic degree:

<person>

<title>Prof. Dr. med.</title>

<name>Friedrich Busch</name>

</person>

XML documents can import things from various sources→ “name clashes” are inevitable.


XML Namespaces

Namespaces define a set of element names used in one document andserve to disambiguate elements with the same name from differentsources

Namespaces can be used in tags with <prefix:elementName>

B Using the namespace books for document 1, people for document 2solves the disambigation problem:

<books:title>Max und Moritz</books:title>

is clearly different from

<people:title>Prof. Dr. med.</people:title>


XML Namespaces

Namespaces define a set of element names used in one document andserve to disambiguate elements with the same name from differentsources

Namespaces can be used in tags with <prefix:elementName>

B Using the namespace books for document 1, people for document 2solves the disambigation problem:

<books:title>Max und Moritz</books:title>

is clearly different from

<people:title>Prof. Dr. med.</people:title>


Example with Namespaces


<ex:pets

xmlns:ex="http://www.example.org/#"

xmlns:cust="http://www.examplecustomers.org/people/#" >


<ex:pet>

<ex:name>Fifi</ex:name>

<ex:petType>Dog</ex:petType>

<ex:dateOfBirth></ex:dateOfBirth>

<ex:owner>

<cust:name>Jane Doe</cust:name>

<cust:city>Heretown</cust:city>

</ex:owner>

</ex:pet>

</ex:pets>


Quiz: Namespaces

Given the following namespace prefixes:

PREFIX ex: <http://www.example.org/#>

PREFIX bsp: <http://www.example.org/#>

PREFIX ims: <http://www.ims.uni-stuttgart.de/#>

Which URIs refer to http://www.example.org/#SemanticWeb?

A) http://www.example.org/SemanticWeb

B) ex:SemanticWeb

C) bsp:SemanticWeb

D) ex#SemanticWeb

E) ims:SemanticWeb


Outline

1 Recap




5 XML Namespaces


7 Summary

8 References


XML Schema: Defining XML in XML

XML Schema offers a language for defining the syntactic structure ofXML documents1

This means an XML Schema defines which types of elements andattributes are allowed in which places inside an XML document

XML Schema provides a set of predefined data types that are widelyused

1An older, less powerful method for doing this is by using DTDsC. Thorne (IMS Stuttgart) Basic Technologies SemWeb, SS 2017 28 / 35

XML Schema Data Types

PREFIX xsd: <http://www.w3.org/2001/XMLSchema/#>

Some predefined data types:

Text xsd:string, . . .

Numbers xsd:int, xsd:integer, xsd:nonNegativeInteger,xsd:positiveInteger, . . .

Decimals xsd:decimal, xsd:float, xsd:double, . . .

Dates xsd:date, xsd:dateTime, . . .

Boolean xsd:boolean

URIs xsd:anyURI

B Used to type elements


Example XML Schema




<schema

xmlns:xsd="http://www.w3.org/2001/XMLSchema/#"

xmlns:hello="http://example.com/HelloWorld/#"

targetNamespace="http://example.com/HelloWorld/#">

<xsd:complexType="employee"

<xsd:sequence>

<xsd:element name="name" type="xsd:string">

<xsd:attribute name="email" type:"xsd:string">

</xsd:element>

<xsd:element name="id" type="xsd:integer"/>

<xsd:element name="income" type="xsd:string"/>

</xsd:sequence>

</xsd:complexType>

</schema>


Example XML File




<hello:employee

xmlns:hello="http://example.com/HelloWorld/#"

<hello:name hello:email="[email protected]">

John Doe

</hello:name>

<hello:id/>

<hello:income>28,000,000</hello:income>

</hello:employee>


Outline

1 Recap




5 XML Namespaces


7 Summary

8 References


Summary: Semantic Web Basis Technologies

Unicode is a mapping from writing characters of any writing systemto abstract code points.

UTF-8 is an encoding for unicode code points.

A URI is a unique identifier for a specific resource.

XML is a format for exchanging data between applications.

XML has no predefined tags, for exchanging data applications have toagree on a common vocabulary (a set of tags with specified meaning).

Namespaces serve to disambiguate XML elements from differentsources and make URIs more readable.

XML Schema describes the syntax of XML documents and providesa set of common data types.


Outline

1 Recap




5 XML Namespaces


7 Summary

8 References


Suggested Reading

Pascal Hitzler, Markus Krotzsch, Sebastian Rudolph and York Sure.Semantic Web. Grundlagen. Springer textbook, 2008. (Chapter 2)

Pascal Hitzler, Markus Krotzsch and Sebastian Rudolph. Foundationsof Semantic Web Technologies. Chapman & Hall/CRC, 2009.(Appendix A)