Mission Possible: Deploying Government Linked Data (Pt2)

Sandro Hawke, (sandro@w3.org), W3C/MIT, @sandhawke
John L. Sheridan, @johnlsheridan
gov 2.0 expo, May 25-26, 2010, Washington DC
http://www.w3.org/2010/Talks/0525-rdf-vocabularies (wiki)

Part 2

Viewing Your Data as Triples

Good URIs
Properties (relationships and attributes)
Competition and Overlap
Classes
Vocabularies

Vocabulary as Interface

How do programs communicate via triples?

Alice and Bob publish triples, Charlie's software tries to use their data.

It's all about the specific URIs, the vocabulary.

Essentially, when using RDF, the vocabulary is the syntax, the API.

Example: Crime Reports

@@@ example of integrating crime data from multiple agencies

Identify Your Subjects

What are the things your data is about?

the items, entities, objects, individuals, ...

See UML, Database Records, your web site

Assign Good URIs

give them good, long-term URI names

Pick URIs that:

no one will want for something else
that may become unfashionable, but wont become wrong
that someone will web-serve forever

Such as:

See Designing URI Sets for the UK Public Sector

Properties

Essential to understand a triple, the middle part

Also known as:

relation, relationship,
predicate
column, column-name
attribute
field, member, slot (sort of)

@@@ maybe SQL example

Property As Question

Each triple is the answer to a question.

The subject: the item the question is about
- you, me, Massachusetts, the moon, crude oil, ... whatever
The property: the question
- who created it? when was it created? where is it located?
The value: the answer to the question

Object and Data Properties

A Data Property:

value is a literal (string, number, date, etc)
- data_created, height, weight, name, name_of_owner

An Object Property:

value is another first-class entity (not just a literal)
- owner, near, friend, hometown, capital

Data Types

@@@ xml data types

Some Well-Known Properties

@@@ make these be links to real documentation

rdfs:label

rdfs:comment

owl:sameAs

foaf:name

dc:creator

Overlapping, Competing Vocabularies

two terms for the same thing

two terms for very similar things

owl:sameAs

owl:equivalentProperty

dc:creator owl:equivalentProperty dcterms:creator
foaf:name owl:equivalentProperty vcard:FN

Subproperty

(dc refines)

rdfs:subPropertyOf

sandro contact john
- sandro friend john
  - sandro recentFriend john
- sandro presentedWith john

friend rdfs:subPropertyOf contact
recentFriend rdfs:subPropertyOf friend
presentedWith rdfs:subPropertyOf contact

geographically near, overlapping, contained-within

Messy Overlap

Not all related properties are equiv or sub

foaf:firstName, foaf:givenName, foaf:lastName, foaf:familyName, foaf:name

Compare: http://dbpedia.org/resource/Barack_Obama http://www.cyc.com/2004/06/04/cyc#UnitedStatesPresident (@eh,that's just a class)

Conversion Rules

        if { ?x foaf:firstName ?first;
                foaf:lastName ?last }
        then
           { ?x foaf:familyName ?last;
                foaf:givenName ?first;
                foaf:name func:string-join(?first " " ?last)
           }

        if { ?x foaf:name ?name } and
           pred:contains(?name, " ")
        then
           # incorrect if lastname has space, like Hillary Rodham Clinton
           { ?x foaf:firstName func:string-before(?name, " ");
                foaf:lastName func:string-after(?name, " ")
           }

See Rule Interchange Format

Applying Rules

In custom code, or using rules engine
In producer (publish using many vocabs)
In consumer (accept many vocabs)

Advice?

The world is full of competing standards. That's good, but painful.

Probably best to follow Postel's Law:

 Be conservative in what you do; be liberal in what you accept from others.

Research topic: automatic downloading of conversion rules

Classes and Subclasses

Sets of objects with something in common.

Instances / rdf:type

Subclass hierarchy

plant / large_plant / tree / mature_horse_chestnut, the one in my back yard

Domain and Range

domain: the class of things which might have this property.

range: the class of possible values for this property

@@ table of domain and range for various example properties

OWL

Powerful way of declaring how properties, classes, and individuals relate to each other.

"Ontologies"

http://www.w3.org/TR/owl2-primer/

class expressions ( US_Citizen and Irish_Citizen and not Minor )
ChildofSandro (anythin with 'parent' being Sandro)
BigTree (trees with height over 30 feet)
inverse properties
- Sandro child Gregorian
- Gregorian parent Sandro
- => parent owl:inverseOf child
negative assertions (some triple is false)

OWL can be conveyed in triples, but also has some easier-to-read syntaxes. I suggest Manchester, when you don't need triples.