O N T O P E D I A. The Identity of Everything. Subject Identity. Steve Pepper. INF5909,

Transcription

1 Subject Identity Steve Pepper INF5909,

2 Agenda Merging in Topic Maps The Importance of Identity The Topic Maps Approach to Identity The Identity Crisis of the Web Published Subjects (Subject-centric Computing)

3 Merging in Topic Maps An Example of Knowledge Federation

4 Merging topic maps Topic Maps can be merged automatically Arbitrary topic maps can be merged into a single topic map This cannot be done with databases or XML documents Merging enables many advanced applications Information integration across repositories Sharing and reusing taxonomies Automated content aggregation Distributed knowledge management Global knowledge federation Merging made possible by subject identity

5 Principles of merging By definition: Every topic represents exactly one subject The goal: Every subject represented by exactly one topic name 1. When two topic maps are merged, topics that represent the same subject should be merged to a single topic 2. When two topics are merged, the resulting topic has the union of the characteristics of the two original topics name name T occurrence occurrence association role association role association role name T occurrence name...and Merge the resulting the two topics has together... association the union role of the original characteristics (Demo of merging in the Omnigator ) A second topic (in another topic map) about the same subject

6 The vision of seamless knowledge Starting with ITU in 2001, Norway has seen an explosion in the number of portals that are based on Topic Maps Today there are dozens, especially in the public section As the number of portals multiplies, the amount of overlap increases The potential for integration is staggering Take these three portals as an example: forskning.no (Research Council web site aimed at young adults) forbrukerportalen.no (Norwegian Consumer Association) matportalen.no (Biosecurity portal of the Department of Agriculture)

7 Genetically modified food at forskning.no

8 Genetically modified food at Forbukerrådet Terefe Badenod

9 Genetically modified foodstuffs at Matportalen

10 Three portals one subject one virtual portal with seamless navigation in all directions

11 The Importance of Identity

12 Identity and knowledge federation Knowledge federation requires subject-based merging subject subject

13 The big challenge is Knowing when we re talking about the same thing the real world the computer domain

14 Humans get by using names But names are ambiguous (homonyms) Humans disambiguate using (a) context and (b) negotiation Many names have the same referent (synonyms) Humans can generally handle this Computers can t at least not without our help... Computers need a simpler mechanism Local identifiers (database keys, XML IDs, controlled vocabularies, code sets, etc.) work OK in closed systems but not across systems or domains (e.g. the code nor ) Open and multilingual systems need global identifiers

15 Requirements on global identifiers The mechanism as a whole should be open and democratic: top-down solutions won t work scaleable: the number of potential subjects is open-ended easy to adopt: based on existing tools and methods The identifiers themselves should be easy for humans to use: locate, create, interpret, apply given a subject, find an identifier (if one exists) given a subject, create an identifier given an identifier, find out what subject it identifies given an identifier, attach it to the information in question efficient for computers to use: comparison of identifiers lexical comparison simplest avoid normalization, network access, other computation

16 Some proposed solutions URL based proposals For web documents HTTP URIs (URLs) address = identifier For resources in general Source: SemWeb community URIs for arbitrary resources (esp. classes og properties) Published Subjects Source: Topic Maps community Continuation of SemWeb practice Non-URL based proposals URN (RFC 1737) Uniform Resource Names XRI (OASIS) Extensible Resource Identifiers Domain specific ISBN (books) DOI ( digital objects ) GUID & UUID UPC & EAN RFID (what else is out there?)

17 The Topic Maps Approach to Identity Direct identification (subject locators) Indirect identification (subject identifiers)

18 Subjects and topics Topics are surrogates, or proxies (inside the computer) for the ineffable subjects that you want to talk about, such as Puccini, love, these slides, or the second law of thermodynamics A subject in the real world (referent) T A topic in the computer domain (symbol)

19 Topics and subjects Topics represent subjects By definition every topic represents exactly one subject The goal when merging is to ensure that every subject is represented by exactly one topic (the collocation objective) A subject can be anything you want ISO definition: A subject is any thing whatsoever, whether or not it exists or has any other specific characteristics, about which anything whatsoever may be asserted by any means whatsoever. Some examples... (Tosca) (Puccini) (Lucca) (Madame Butterfly)

20 The identity of subjects Topics exist in order to allow us to talk about subjects The relationship between the two is sometimes called intentionality We need to know exactly which subject a topic represents That is, we need to establish its subject identity The collocation objective depends on knowing when applications are talking about the same thing Lucca Puccini Tosca Madame Butterfly

21 Subject locators (These slides) O N T O P E D I A Subject Identity Steve Pepper pepper.steve@gmail.com INF5909, Sometimes the subject is an information resource (like these slides) subject It exists somewhere within the computer system It has a location and can be addressed, e.g. The address of such an addressable subject can be used to unequivocably establish the subject s identity An address used in this way to identify a subject directly is called a subject locator But most subjects are not information resources subject locator Puccini, Tosca, love, subject-centric computing, Outside the computer domain and cannot be addressed directly... topic

22 Subject identifiers Life, the Universe and Everything subject The identity of most subjects can only be established indirectly An information resource can provide an indication of the subject s identity to a human Such a resource is called a subject descriptor* A subject descriptor has an address, even though the subject it indicates does not Computers can use the address of the subject descriptor to establish identity Such addresses are called subject identifiers Subject descriptors and subject identifiers represent the two faces of the human-computer dichotomy * also known as subject indicator The Topic Map Domain The Computer Domain Puccini topic subject identifier Giacomo Puccini, Italian composer, b. Lucca 22nd Dec 1858, d. Brussels, 29th Nov Best known for his operas, of which Tosca is the most... subject descriptor

23 A dual mechanism The subject is identified by a URL The URL is called a subject identifier topic Giacomo Puccini subject identifier subject The URL is the address of a web page The web page describes the subject such that a human can know what subject is referred to This web page is called a subject descriptor Giacomo Puccini Italian composer, b. Lucca 22nd Dec 1858, d. Brussels, 29th Nov Best known for his operas, of which Tosca is one of the most popular and well-known. subject descriptor Machines use the identifier The link is not resolved. Instead simple lexical comparison is used. If the strings are identical, the subject is deemed to be the same and the topics are merged. Humans use the descriptor By inspecting the web page the person responsible for assigning the identifier can be sure that it does not refer to, say, Giacomo s grandfather Domenico (who was also a composer of operas)

24 Summary of the TM approach Allows both direct and indirect identification of subjects Direct identification is for information resources addressable subjects only subject locators (orig. subject addresses) Indirect identification is for anything both addressable and non-addressable subjects subject identifiers and subject descriptors (orig. subject indicators) There is also a construct called item identifier used under the covers for mapping between syntax and internal representation

25 The Identity Crisis of the Web Also known as the httprange14 issue

26 Identity crisis Article on XML.com September 2002 by Kendall Clark Based on a review of the work of the W3C s Technical Architecture Group (TAG) Architectural Principles of the World Wide Web Part of a larger discussion in the Web community What do HTTP URIs identify? (Tim Berners-Lee) Disambiguating RDF Identifiers (Sandro Hawke) Four Uses of a URL (David Booth) Web Proper Names (Harry Halpin & Henry S. Thompson)

27 The problem in a nutshell: What do URIs identify? Sandro Hawke: To date, RDF has not been clear about whether a URI like identifies the W3C or a web page about the W3C. Throughout RDF, strings like are used with no consistent explanation of how they relate to the web. Why is this important? Because without clarity on this issue The challenge of the Semantic Web cannot be solved Web services cannot be implemented in a scaleable manner Ontologies and taxonomies will not be reusable The goal of Global Knowledge Federation is unreachable The problem of Infoglut will never go away

28 Introducing Eric Miller Formerly of OCLC: Dublin Core, RDF Later Technical Lead of the W3C s Semantic Web Activity I see both RDF as well as Topic Maps working toward enabling the Semantic Web

29 A simple example (1) RDF Primer Example 1: RDF/XML Describing Eric Miller <rdf:rdf xmlns:rdf=" xmlns:contact=" <contact:person rdf:about=" <contact:fullname>eric Miller</contact:fullName> <contact:mailbox <contact:personaltitle>dr.</contact:personaltitle> </contact:person> </rdf:rdf>

30 A simple example (2) Person Eric Miller Dr.

31 Resolving the URI Clicking on this URL displays the following document <?xml version="1.0"?> <rdf:rdf xmlns:rdf=" xmlns=" <Person rdf:about=" <rdf:value>eric Miller, <mailbox /> <fullname>eric Miller</fullName> <personaltitle>semantic Web Activity Lead</personalTitle> <company>w3c World Wide Web Consortium</company> <phone> </phone> </Person> </rdf:rdf> April 2nd 2002 dc:creation-date Now let s add some DC metadata to this document

32 Encoding the metadata in RDF Ex2: RDF/XML Describing the document about EM <rdf:rdf xmlns:rdf=" xmlns:dc=" <rdf:description rdf:about=" <dc:creator>eric Miller</dc:creator> <dc:creation-date>2002/06/04</dc:creation-date> </rdf:description> </rdf:rdf> Person Dr. dc:creation-date Document about April 2nd 2002 Eric Miller / Eric Miller dc:creator

33 The cause of the problem URIs are being used for two distinct purposes To identify information resources To identify the thing that an information resource describes or indicates And we don t know the difference!

34 Problem recognized in W3C Architectural Principles of the World Wide Web: 2.2. Uses of URIs The two primary uses of URIs are (1) To compare identifiers and (2) Dereference a URI (that is, as identifiers and as addresses) Consistent use of URIs It is confusing and costly when people use the same URI to refer to different resources (i.e., where there is some inconsistency in usage compared to the authoritative meaning of the resource). Suppose company A uses to refer to CoolCompany's home page, while company B uses to refer to CoolCompany. Company A then buys company B, but when they try to merge their databases, they cannot due to this inconsistent usage of the URI.

35 Original solution (2003) was ineffectual handwaving: Consistent use of URIs Good practice: Consistent URIs: Indiscriminate use of a URI undermines its value and interferes with people who rely on it. In fairness, individuals in the Web and RDF communities have proposed solutions Larry Masinter: tdb URN namespace ( Thing Described By ) Sandro Hawke: Distinguish between page mode and subject mode David Booth: Distinguish between names, concepts, web locations, and documents Not taken seriously by the W3C (There is also the hash/slash proposal)

36 How the situation came about In the Beginning the Web was a web of information resources URIs (Uniform Resource Identifiers) originally called UDIs (Uniform Document Identifiers) Name changed to avoid narrow interpretation of document But resources were still information resources Most important kind of URI was the URL the Uniform Resource Locator A locator is the address of something (e.g., an information resource) An address is a fairly robust way of identifying something So URLs started to be regarded as identifiers All of this worked fine until someone had the bright idea of using URLs to identify things that were not information resources...

37 Redefining resource Imperceptibly, resource acquired a new meaning No longer just an information resource Came to mean anything whatsoever Practice codified in RFC 2396 in August 1998 A resource can be anything that has identity. Familiar examples include an electronic document, an image, a service (e.g., "today's weather report for Los Angeles"), and a collection of other resources. Not all resources are network "retrievable"; e.g., human beings, corporations, and bound books in a library can also be considered resources. (RFC 2396) This was a mistake Because it obscures a fundamental ontological feature of the Web that information resources have special significance

38 Information resources are special They have locations within the system A document has an address, a location Any information resource has an address The address can be used to identify the resource But nothing else has an address Eric Miller does not have a location within the computer system This fundamental ontological fact is recognized in Topic Maps Direct identification vs. indirect identification Not recognized in RDF, or the Web Architecture in general

39 URIs as resource identifiers subject locator

40 URIs as arbitrary subject identifiers subject descriptor

41 httprange14: The TAG s resolution Agreed on 15 Jun 2005: The TAG provides advice to the community that they may mint "http" URIs for any resource provided that they follow this simple rule for the sake of removing ambiguity: If an "http" resource responds to a GET request with a 2xx response, then the resource identified by that URI is an information resource; If an "http" resource responds to a GET request with a 303 (See Other) response, then the resource identified by that URI could be any resource; If an "http" resource responds to a GET request with a 4xx (error) response, then the nature of the resource is unknown. This resolution (known as the 303 hack ) has not ended the debate...

42 Published Subjects

43 Published Subjects In order for identifiers to be reused, they must made publicly available A subject identifier that has been made available for use outside one particular application is called a published subject identifier (PSI) Its descriptor is called a published subject descriptor (PSD) Anyone can publish PSI sets Adoption of PSI sets will be an evolutionary process based on trust It will lead to greater and greater interoperability between topic map applications, between Topic Maps and RDF, and across information and knowledge management in general Check out (under development)

44 What is Published Subjects? An extremely simple mechanism (or convention) for defining and sharing globally unique identifiers for arbitrary subjects The identifier is an HTTP URI (i.e. a URL) It s called a published subject identifier (PSI) It resolves to a web page The contents of this page convey the identity of the subject in a form that is human-interpretable This pages is called a published subject descriptor* (PSD)

45 The advantages of PSIs URLs (HTTP URIs) are easier to use than, e.g. URNs The resolution mechanism is now very widely supported The PSI / PSD duality is simple and useful Makes it possible for users to understand the publisher s intentionality Open and democratic Anyone can create a PSI no top-down supervision Common sets of PSI can emerge through consensus based on Trust in the publisher (stability, longevity) Degree of adoption in particular communities

46 A little terminologi Topic Maps standard (1999) Public Subjects Public Subject Descriptor XTM 1.0 (2001) Published Subject Indicator (PSI) OASIS PubSubj TC (2003) Published Subject Indicator (PSI) Published Subject Identifier (PSID) W3C Call for Action (2006) Public Resource Identifier (PRI) Public Resource Descriptor (PRD) Current usage PSI abbreviation for the identifier Confusion identifier / indicator My proposal Published Subject Identifier (PSI) Published Subject Descriptor (PSD) Rationale PSI most often used for the identifier Term indicator a little too opaque Identifier and indicator too similar One abbreviation for two different terms leads to confusion

47 Proposed definitions Published Subjects a paradigm for creating globally unique identifiers for arbitrary subjects published subject a subject for which a published subject identifier has been published published subject identifier (PSI) a HTTP URI that was created explicitly for the purpose of serving as the identifier for some subject published subject descriptor (PSD) an information resource to which a published subject identifier resolves and whose purpose is to convey to a human the identity of the subject thus identified, i.e. the intentionality of the publisher of the PSI

48 OASIS PubSubj TC (oppdatert) Requirements A PSI must be a URI A PSI must resolve to a PSD A PSD must explicitly state its PSI Recommendations A PSD should provide human-readable metadata A PSD may provide machine-readable metadata Human-readable and machine-readable metadata should be consistent but need not be equivalent A PSD should indicate its intended use as a PSD A PSD should identify its publisher

49 Frequently Asked Questions What happens if two people create PSIs for the same subject? This will happen, but it s no catastrophe Over time, stable sets of PSIs will emerge as de facto standards In the interim, mapping between PSIs (or between PSI sets) is simple With structured information, batch updates of identifiers is easy How do I go about finding a PSI? As of today there are no registries or lookup services We envisage an open, distributed system based on, or similar to, UDDI What if I disagree with assertions made by the publisher? Doesn t matter. You aren t being asked to agree! The assertions are only there to give you sufficient indication of the identity of the subject to be able to decide if it s the same subject as the one you re interested in.

50 Discussion points Should we only use HTTP URIs? Only HTTP URIs have a widely supported resolution mechanism What form should the URI take? Readability, use of fragment identifiers, queries, etc. Are Wikipedia URLs suitable? If so, what about other sources, e.g. Ethnologue What information should a PSD contain? Content of descriptor itself, metadata What kinds of discovery mechanism could be used? Registries, search engines,... What is the role of the PSI server? In addition to published the PSD, what services might it offer? Norwegian terminology publisert tema, publisert temaidentifikator, publisert temadeskriptor?