lis512 lecture 6

1. lis512 lecture 6 identifiers, dublin core and RDF

2. identifiers • When you are maintaining your information on your own, you don't exchange it, you don't need to worry about identifiers. • Identifiers come into play when you try to communicated to another party that • you are talking about the some thing as before or • the other party and you mean the same thing.

3. keys • We have already seen keys in a database. • A key is simply a column in a table that is unique in for each line in in the table. • A key is simply a field in a record that is unique for each record in a table.

4. identifier • An identifier is something a bit different. • When two records have the same identifier, they are about the same thing. • Being about the same thing calls the philosophers into the room. • Things become pretty messy. • Discussion on identifiers is often very confused, even among experts.

5. example • Record 1 • Name: Thomas Krichel • Homepage: http://wotan.liu.edu/home/krichel • Record 2 • Name: Thomas Krichel • Homepage: http://openlib.org/home/krichel • Are they about the same person?

6. a person homepage finder • Imagine a home page finder. • Ask it what the homepage of Thomas Krichel is. • It may say that there are two Thomas Krichels with two different homepages. • If there is only one, the service is wrong.

7. work to do • If we have two records that look like we describe the same person, we try to unite them. • In a practical scenario, we most of the time have a first Thomas Krichel. • When the other Thomas Krichel comes along, we check, make a decision if it is the same person, then update the homepage setting.

8. human labour • To find out if a person is the same as another person is something that no computer can do. • We need a person to verify this. • Identity can only be controlled by a person. • Worst: two people may differ on what “same person” means.

9. identifier • The identifier is a special field that we keep constant over time as long as the record is about the some thing. • When we get our first record about Thomas Krichel, we have • Name: Thomas Krichel • Homepage: http://openlib.org/home/krichel • Identifier: tk1

10. changes to the record • Thomas gets married • Name: Thomas Lechirk • Homepage: http://openlib.org/home/krichel • Identifier: tk1 • Later, he decides to change his hompage • Name: Thomas Lechirk • Homepage: http://openlib.org/home/lechirk • Identifier: tk1

11. problem • Since he is now know as Thomas Lechirk, should he not be given an identifier tl1? • Well in general, the resultion of this question depends on the enviroment that we are operating in. • Changing the identifier would destroy its value.

12. value of the identifier • If you change the identifier every time you change the record, it is useless. • The value of the identifier is that is long-lived. • With a good idenifier, users will still be able to find the same thing even when they query the same dataset in hundreds of years.

13. dumb vs intelligent identifiers • Identifiers can be dumb or intelligent. • Choosing a scheme for identifiers is a key step at the start of a project. • Once we are running our project, changing identifiers can only be accomplished at great expense. • Dump identifiers are strings that have no meaning or structure “na$19h-ab9a19]”

14. dumb indentifiers • The advantages are • If they are long and complicated enough they may be found by web searches. • They are not at risk from lobbying for change. • The problem is • It is not easy to resolve the identifier into data about.

15. intelligent identifiers • Most identifiers have some form of intelligence. • That intelligence says something about the identifier to a person who looks at it. • The intelligence may also help a computer program to make decisions.

16. ISBN • An ISBN is assigned to each edition of a book. • After 2007, it has 13 numbers, the first 3 are 978 or 978. Before 2007, it had only the remaining 10. • Digits 1 to 5 are the group identifier for country or country group. • Then follows a publisher identifier. • Then follows an item number by the publisher. • The parts are often split by hyphens but the hyphen is not part of the actual number.

17. Uniform Resource Locators URL • We all know URLs. • Speaking in simplified terms, a URL typically has three components. • a mechanism • a host • a local part, local to the host

18. URL mechanism • The URL mechanism essentially says what to do with the thing when you actually find it. • Typical URL mechanisms include • http • ftp • telnet • mailto

19. host • The host is the domain name of a machine. • Domain names are a hierarchical scheme of names that can be resolved into IP addresses. • Example • openlib.org • fafner.openlib.org • www.fafner.openlib.org • I lease openlib.org.

20. local part • Once the resolution reaches the host it needs to know what to send out. • This is some sort of local identifier that the host knows about.

21. URIs • The world wide web consortium, in its quest to make the web a more universal information medium, generalized URLs to URIs. • URI are Uniform Resource Identifiers. • The don't only allow for locating resources but also for naming them. • The structure is similar, but there is a wide variety of mechanisms, called schemes.

22. example scheme info • The info: URI scheme was created by representatives of the library community and the publishing industry as a light-weight way to make existing identifiers available as URIs. • http://info-uri.info/ has the list of these schemes.

23. URL examples • http://openlib.org/home/krichel/ • mechanism: http • host: openlib.org • local part: /home/krichel/ • mailto:krichel@openlib.org • mechanism: mailto • host: openlib.org • local part: krichel

24. DC contributor • URI http://purl.org/dc/elements/1.1/contributor • Definition: An entity responsible for making contributions to the resource. • Comment: Examples of a Contributor include a person, an organization, or a service. Typically, the name of a Contributor should be used to indicate the entity.

25. Dublin Core • Dublin Core was initially created at a invitational meeting at OCLC in Dublin, OH. • The aim was to create a metadata format that non-trained specialists could use the annotate resources on the Web. • Nowadays, it serves as a basic common denominator metadata in a wide variety of applications.

26. DC coverage • URI http://purl.org/dc/elements/1.1/coverage • Definition: The spatial or temporal topic of the resource, the spatial applicability of the resource, or the jurisdiction under which the resource is relevant. • Comment: Spatial topic and spatial applicability may be a named place or a location specified by its geographic coordinates. Temporal topic may be a named period, date, or date range.

27. DC creator • URI http://purl.org/dc/elements/1.1/creator • Definition: An entity primarily responsible for making the resource. • Comment: Examples of a Creator include a person, an organization, or a service. Typically, the name of a Creator should be used to indicate the entity.

28. DC date • URI: http://purl.org/dc/elements/1.1/date • Definition: A point or period of time associated with an event in the lifecycle of the resource. • Comment: Date may be used to express temporal information at any level of granularity. Recommended best practice is to use an encoding scheme.

29. DC description • http://purl.org/dc/elements/1.1/description • Definition: An account of the resource. • Comment: Description may include but is not limited to: • an abstract • a table of contents • a graphical representation, or • a free-text account of the resource.

30. DC format • http://purl.org/dc/elements/1.1/format • Definition: The file format, physical medium, or dimensions of the resource. • Comment: Examples of dimensions include size and duration. Recommended best practice is to use a controlled vocabulary. • The MIME types by the IANA are such a vocabulary for files.

31. DC identifier • URI: http://purl.org/dc/elements/1.1/identifier • Definition: An unambiguous reference to the resource within a given context. • Comment: Recommended best practice is to identify the resource by means of a string conforming to a formal identification system.

32. DC language • URI: http://purl.org/dc/elements/1.1/language • Definition: A language of the resource. • Comment: Recommended best practice is to use a controlled vocabulary such as RFC 4646

33. DC publisher • URI: http://purl.org/dc/elements/1.1/publisher • Definition: An entity responsible for making the resource available. • Comment: Examples of a Publisher include a person, an organization, or a service. Typically, the name of a Publisher should be used to indicate the entity.

34. DC relation • URI: http://purl.org/dc/elements/1.1/relation • Definition: A related resource. • Comment: Recommended best practice is to identify the related resource by means of a string conforming to a formal identification system.

35. DC source • URI: http://purl.org/dc/elements/1.1/source • Definition: A related resource from which the described resource is derived. • Comment: The described resource may be derived from the related resource in whole or in part. Recommended best practice is to identify the related resource by means of a string conforming to a formal identification system. • Apparently only kept for historical purposes.

36. DC subject • URI: http://purl.org/dc/elements/1.1/subject Definition: The topic of the resource. Comment: Typically, the subject will be represented using keywords, key phrases, or classification codes. Recommended best practice is to use a controlled vocabulary. To describe the spatial or temporal topic of the resource, use the DC coverage element.

37. DC title • URI: http://purl.org/dc/elements/1.1/title Definition: A name given to the resource. Comment: Typically, a Title will be a name by which the resource is formally known.

38. DC type • URI: http://purl.org/dc/elements/1.1/type • Definition: The nature or genre of the resource. • Comment: Recommended best practice is to use a controlled vocabulary such as the DCMI Type Vocabulary • To describe the file format, physical medium, or dimensions of the resource, use the DC Format element.

39. DC abstract model • Basically, this is something like the FRBR for Dublin Core. • It maybe quite useless in practice, but it makes for beautiful theory.

40. the resource • A resource is anything that can be given an identifier. • Since a URI can be given to almost everything, this includes a vast array of "stuff". • But the important thing is that the resource is actually identified by some identifier, rather than being named. • It's essentially same thing as an entity in FRBR.

41. property / value pair • A description occurs when a bunch of attribute / value pairs are associated with a resource. • This is like the attributes in FRBR, just that it counts them together with the values.

42. property values • Property values can be of two forms. • They can be literals, i.e. human understandable strings. • Or they can be resources, which again can be described. When a resource is used as a value, we quote an identifier.

43. example • Resource: http://openlib.org/home/krichel • DC.Creator: Thomas Krichel • DC.Format: text/html • Note: properties themselves are identified by URIs.

44. similar: the resource description framework • The resource description framework has been developed by the W3C is a way generically represent information, such that it can be processed via the Web. • It again is a conceptual model. • RDF can be expressed in a variety of syntaxes. • The XML syntax of RDF is very ugly.

45. general idea • The general idea is that of a semantic web. • Such a semantic web you could ask real questions such as what we will tomorrows weather here, or what athlete won the most gold medals in the Olympic games of 1936. • Such a system is many years away. • Computer scientists don't make much progress with this.

46. key problem • The key problem is identity. • You and I may understand what a gold medal and what the Olympic games are. • But teaching agreeing on what it precisely means appears to be a matter of great difficulty. • Recently, some research, the dbpedia, used wikipedia headings as concept names.