1oreilly enterprise java conference, 2001an introduction to rdf

1An Introduction to RDF O’Reilly Enterprise Java Conference, 2001


Facilities to put machine-understandable data on the Web are becoming a high priority for many communities. The Web can reach its full potential only if it becomes a place where data can be shared and processed by automated tools as well as by people. For the Web to scale, tomorrow's programs must be able to share and process data even when these programs have been designed totally independently. The Semantic Web is a vision: the idea of having data on the web defined and linked in a way that it can be used by machines not just for display purposes, but for automation, integration and reuse of data across various applications.


History


What is the Web, Really ?

• Millions upon millions of computers all using the same communications protocol

TCP/IP

HTTP

HTML

HTMLDEPARTMENT OF MATHEMATICS AND COMPUTER SCIENCESAN JOSE STATE UNIVERSITYSPRING 2000 COLLOQUIUM SERIES, PART IIEach talk with be on a Thursday at 3:00 p.m. in MacQuarrie Hall 523 Please join us for refreshments beforehand, at 2:30 p.m., in MacQuarrie Hall 210Parking available in the Seventh Street Garage at South Seventh and San Salvador Streets, San Jose, CAApril 6 Zvezdelina Stankova-Frenkel, Mathematics, Mills College

From Desargues to Modern Algebraic GeometryWe will look at some classical plane geometry . . . mathematics.


The Evolution of Web Technology

• HTML 1.0 became 2.0 became ... 4.0

• Cascading style sheets and other formatting and layout standards defined by W3C

• Proprietary technologies such as Shockwave and PDF invented


The Implicit Assumptions

• Point to point (direct) communication

• The primary task of a web server is to deliver information to a human who is asking for that information– Key points: to a human, already asking for

information


The First Business Opportunity

• “The Web is like mail-order”

• Put Catalogs on the web– Easy to update– Easy to link in auxiliary information

• “People who bought that also bought …”

• Availability information

• In many cases, simply putting an “HTML front end” on existing systems


Leads to Another Opportunity

• Catalogs prime the pump– Easy to understand application that is

compelling– Side-effect: lots of information is now available

on the internet

• How do we take advantage of it ?– Automate existing processes– Enable new applications


HTML is a Problem

• It’s a markup language based on document structure– Most tags are visual, about presentation– HTML solves document-level navigation

problems, for humans– Lots of information encoded in images

• Fundamentally, the wrong idea.


eXtensible Markup Language (XML)

• Basically, a language for defining markup languages

• Key idea: separate data from presentation information

• Replace HTML with two things• A domain specific markup language (defined in XML)

• A map from that markup language to HTML (defined using XSL)

Split Data <SEASON><YEAR>1998</YEAR><LEAGUE><LEAGUE_NAME>National League</LEAGUE_NAME><DIVISION><DIVISION_NAME>East</DIVISION_NAME><TEAM><TEAM_CITY>Atlanta</TEAM_CITY><TEAM_NAME>Braves</TEAM_NAME><PLAYER><SURNAME>Malloy</SURNAME><GIVEN_NAME>Marty</GIVEN_NAME><POSITION>Second Base</POSITION><GAMES>11</GAMES><GAMES_STARTED>8</GAMES_STARTED><AT_BATS>28</AT_BATS><RUNS>3</RUNS><HITS>5</HITS><DOUBLES>1</DOUBLES>.....

Meaning!

From: The XML Bible by Harold

From Presentation<HTML xmlns:xsl="http://www.w3.org/TR/WD-xsl"><HEAD><TITLE> <xsl:for-each select="SEASON"> <xsl:value-of select="YEAR"/> </xsl:for-each> Major League Baseball Statistics</TITLE></HEAD><BODY> <xsl:for-each select="SEASON"> <H1 ALIGN="CENTER"> <xsl:value-of select="YEAR"/> Major League Baseball Statistics </H1>

Formatting!


What is the Web, XML Version

• HTML is a tag language, defined using XML– One of many tag languages (and the likely

target for XSL transformations)

TCP/IP

HTTP

XML

XHTML Special Purpose Tag Languages


XML Has Lots of Problems

• Everything bottoms out in strings

• DTD’s provide simple structure at the level of “documents”– Very simple inter-document structure– No provisions for intra-document structure

• No support for versioning

The VISA DTD<!ELEMENT Invoice (InvoiceHeader, InvoiceDetails+, InvoiceSummary)><!ATTLIST Invoice sectorUsageVersion CDATA #IMPLIED > <!ELEMENT InvoiceHeader (InvoiceType, InvoiceStatus, TaxTreatment, DiscountTreatment?, InvoiceTreatment, InvoiceNumber, InvoiceDate, TaxPointDate?, Currency, Party, Party, Party*, Payment?, PONum?, DeliveryNoteNum?, Ref*, Date*, GenText*)><!ELEMENT InvoiceType EMPTY><!ATTLIST InvoiceType stdValue (380|381) "380"

stdName (UNTDID:1001) "UNTDID:1001"> 

<!ELEMENT InvoiceStatus EMPTY><!ATTLIST InvoiceStatus stdValue (9|10|53) "9"

stdName (UNTDID:1225) "UNTDID:1225">

<!ELEMENT TaxTreatment EMPTY><!ATTLIST TaxTreatment stdValue (NIL|GIL|NLL|GLL|NON) "NLL"

stdName (VISA:TAXT) "VISA:TAXT">

<!ELEMENT DiscountTreatment EMPTY><!ATTLIST DiscountTreatment stdValue (UN|UG|TN) "UG"stdName (VISA:DSCT) "VISA:DSCT"> <!ELEMENT InvoiceTreatment EMPTY><!ATTLIST InvoiceTreatment stdValue (P|EP|E) "P"stdName (VISA:INVT) "VISA:INVT">

It Gets Worse

<!ATTLIST InvoiceTreatment stdValue (P|EP|E) "P"stdName (VISA:INVT) "VISA:INVT">



<!ELEMENT InvoiceNumber (#PCDATA)>

<!ELEMENT InvoiceDate (#PCDATA)>

<!ELEMENT TaxPointDate (#PCDATA)>


The Accompanying Prose

• The DTD is 4 pages

• The manual is 182 pages

The aim of this Guide is to provide sufficient information about the XML Invoice Document to enable its implementation. It documents the file structure, the business usage of the elements, and all the elements and attributes in detail.


RDF


Goal: The Semantic Web

• Different sites each maintain small amounts of information

• Sites need to refer to each other’s information with full semantic integrity– Information is maintained by owners and

referred to by other sites– Information should be accessible, and coherent,

in very small chunks


Needed: Precision

• Need the ability to specify things like dates, times, and monetary amounts

• Compile in those VISA comments– The more of this we can do, the less

programmer-hours are needed

• Ultimately, most web-based computation will not involve a browser


Needed: Granularity

• Saying things at the “page” level is too coarse grained

• Small chunks of data necessary– And ability to aggregate into larger chunks

important


Use Classes and Instances

• Objects are a natural way to represent information

• A web page can contain hundreds of instances, each with its own URI

• Hard part is figuring out how to do this in a way that works on the web


Start with Resources

• A resource is a thing you talk about (can reference)

• Everything is a resource

• Resources have URI’s


How to say things in RDF

• Small set of canonical tags • Use XML syntax to define vocabularies• Information asserted via triples

– Assertions require three things:• Subject: What the assertion is about (always a resource)

• Property: A property whose value is being asserted (always a resource)

• Object: The value of the property (either a resource or a primitive value)


Important Tags

• rdf:Description

• rdfs:Class

• rdfs:Property

• rdf:type

• rdfs:subClassOf

• rdfs:domain

• rdfs:range

Defining a Class

<?xml version='1.0' encoding='ISO-8859-1'?><rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/TR/1999/PR-rdf-schema-19990303#" xmlns:rdfutil="http://www.w3.org/rdfutil#" xmlns:bill="http://www.grosso.org/rdfexample#">

<rdf:Description rdf:ID="MotorVehicle"> <rdf:type resource="http://www.w3.org/TR/1999/PR-rdf-schema-19990303#Class"/> <rdfs:subClassOf rdf:resource="http://www.w3.org/TR/1999/PR-rdf-schema-19990303#Resource"/></rdf:Description>

An Instance of Motor Vehicle

<?xml version='1.0' encoding='ISO-8859-1'?><rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:rdfs="http://www.w3.org/TR/1999/PR-rdf-schema-19990303#" xmlns:rdfutil="http://www.w3.org/rdfutil#" xmlns:bill="http://www.grosso.org/rdfexample#">

<rdf:Description rdf:ID="MyChevy"> <rdf:type resource= bill:MotorVehicle /></rdf:Description>

Resources Define Tags

<rdfs:Class ID="MotorVehicle"> <rdfs:subClassOf rdf:resource="http://www.w3.org/TR/1999/PR-rdf-schema-19990303#Resource"/> </rdfs:Class>

<bill:MotorVehicle ID=MyChevy/>


Classes

• Object-oriented notion

• There are classes, arranged in a taxonomy (with subclass relationships)

• Instances can be instances of more than one class

Adding a Property <rdf:Description rdf:ID="rearSeatLegRoom"> <rdf:type resource="http://www.w3.org/TR/1999/PR-rdf-schema-19990303#Property"/> <rdfs:domain rdf:resource="#MotorVehicle"/> <rdfs:range rdf:resource="http://www.w3.org/TR/xmlschema-2/#integer"/> </rdf:Description>

<rdfs:Property ID=”rearSeatLegRoom"> <rdfs:domain rdf:resource="#MotorVehicle"/> <rdfs:range rdf:resource="http://www.w3.org/TR/xmlschema-2/#integer"/> </rdfs:Property>

Setting Property Values

<rdf:Description rdf:ID=MyChevy><bill:rearSeatLegRoom> 47 </bill:rearSeatLegRoom>

</rdf:Description>


Properties

• Similar to fields (data members, attributes...)• Big difference: they’re first class objects

– Defined independently of classes

– Asserted independently of classes• Classes don’t come with a set of data members• Other people (other pages) can assert properties about

your classes and instances without your knowledge or permission


The Web of Knowledge

Corning Fiberglass has a product catalog

Home Appliances Defines things like

“Blender”

Sears has an on-line store that uses (and extends) both of these

as standard vocabularies





The Web of Knowledge

Public OpinionAnd RatingsTerminology


Home Appliances. Defines things like

“Blender”

Sears has an on-line store that uses (and extends) both of these

as standard vocabularies




Consumer Reports uses the product catalogs and

attaches more informationto them


What is the Web, RDF Version

• Usually called “The Semantic Web”

TCP/IP

HTTP

XML

RDF and RDF-Schema

Schema Schema Schema

Instances Instances


Further Information

• http://www.w3.org/RDF/

• http://www.w3.org/2001/sw/

• http://www.semanticweb.org/

• http://www.mozilla.org/rdf/doc/

• http://www.xml.com/pub/a/2001/01/24/rdf.html

• http://xml.coverpages.org/rdf.html


Programmatic Resources

• Protege (http://www smi.stanford.edu/projects/protege)

• RDF DB (http://web1.guha.com/rdfdb/)• Redland (http://www.redland.opensource.ac.uk/)• Java API

(http://www-db.stanford.edu/~melnik/rdf/api.html)

• Squish (http://swordfish.rdfweb.org/rdfquery/)


High Profile Uses

• Electric Power Industry (http://www.langdale.com.au/XMLCIM.html)

• DMOZ (http://www.dmoz.org/)

• Epinions (http://www.epinions.com)

• DAML (www.daml.org)

1oreilly enterprise java conference, 2001an introduction to rdf

Documents

rdf rdf

rdf slide

rdf xml

information slide

rdf history slide

rdf facilities

xsl slide

versioning slide