A Model for Open Semantic Hyperwikis

Introduction
Model
Conclusions

A Model for Open Semantic Hyperwikis

Philip Boulain

Department of Electronics and Computer Science
University of Southampton

15th September 2009

Philip Boulain A Model for Open Semantic Hyperwikis

Introduction
Model
Conclusions

Outline

1 Introduction
Context

2 Model
Nodes
Functional

3 Conclusions
Composition
Summary


Introduction
Model Context
Conclusions

Outline

1 Introduction
Context

2 Model
Nodes
Functional

3 Conclusions
Composition
Summary


Introduction
Model Context
Conclusions

Broader project

Looking at the potentially beneﬁcial relationships between
Open Hypermedia
Interconnected documents
Semantic Web
Interconnected databases
Wiki Wiki Web
Communal editing systems


Introduction
Model Context
Conclusions

Hypermedia

Long-standing ﬁeld of research.
How can documents expand beyond limitations of paper?
Cross-referencing (hyperlinks).
Sharing and re-use (composition and transclusion).
“Essential feature” is “the process of tying two items
together” (linking).

V. Bush.
As We May Think.
The Atlantic Monthly, 176:101–108, Jul 1945.


Introduction
Model Context
Conclusions

Semantic Web

World Wide Web is a distributed set of interlinked
documents.
The Semantic Web is distributed set of interlinked data.
Discover and combine data from disparate sources as one
may discover and browse web pages.
Core technology is the Resource Description Framework
(RDF).
RDF describes things using triples: subject has predicate
value object.
Subjects, predicates, and non-literal objects named using
URIs.


Introduction
Model Context
Conclusions

Wiki Wiki Web

“A collection of Web pages which can be edited by anyone,
at any time, from anywhere.”1
Users can create pages with much of the structure and
styling of HTML web pages.
But usually in a bespoke ad-hoc markup.
Linking is web-style, like <a href=""></a>.
But some wikis offer the ability to show backlinks.
They can only do this because they are not distributed.
The wiki system is aware of the entire document space.

1
http://c2.com/cgi/wiki?WikiGettingStartedFaq

Introduction
Nodes
Model
Functional
Conclusions

Outline

1 Introduction
Context

2 Model
Nodes
Functional

3 Conclusions
Composition
Summary


Introduction
Nodes
Model
Functional
Conclusions

Nodes

Page, article, component. . . ‘node’ is domain-agnostic.
The fundamental building block of a wiki.
No sub-node addressing in RDF!

Goal
Things we want to address need URIs, not (URI,
within-speciﬁer) pairings.


Introduction
Nodes
Model
Functional
Conclusions

Anatomy

Node title
DOM tree text node
transclude
o_ _ _ _ _
→ native transclusion link
/
DOM element
element contents
attribute "value"


Introduction
Nodes
Model
Functional
Conclusions

Links

Example
I would call [link type=Likes to=Perl Perl] an
[em elegant] language.

Links are nodes.
Links also get embedded in nodes.
Familiar to edit.
Edit-time (native) transclusion of the anchor.
Attributes are our primitive base case.


Introduction
Nodes
Model
Functional
Conclusions

Phil Likes Perl

Phil
I would call
→ Phil.anchor.1
Phil.anchor.1
an _ _ _ _/
Perl
em
elegant
language.

Perl Phil.link.1
(interesting facts) o type Likes
source Phil.anchor.1
syntax elegant target Perl


Introduction
Nodes
Model
Functional
Conclusions

RDF Mapping

Goal
The graph of typed links should be isomorphic to a useful RDF
graph.

Typed links between pages are relations between them.
(Phil, Likes, Perl)
Attributes of a page are statements about it.
(Perl, syntax, elegant)


Introduction
Nodes
Model
Functional
Conclusions

Identity

Every node gets a URI, namespaced within the wiki.
‘The node Perl’ and ‘Perl the programming language’ are
not the same!
The node is http://wiki.example.org/node/Perl.
But our statements are about
http://wiki.example.org/resource/Perl.
Might be owl:sameAs some external Perl.


Introduction
Nodes
Model
Functional
Conclusions

Meta-identity

So how do we refer to the node itself within the wiki?
Perl.meta.
It is http://wiki.example.org/node/Perl/meta
It makes statements about
http://wiki.example.org/node/Perl
There is effectively a naming offset.


Introduction
Nodes
Model
Functional
Conclusions

Representations

node URIs get representation predicates.
(wiki:node/Perl, representation,
http://wiki.example.org/content/Perl.html)
‘303 convention’ deﬁnes retrieval of . . . node/Perl.
RDF requests go to data about the URI: one meta-level
higher.
Otherwise, normal content-negotiation to content.
Can always be explicit if you want RDF-formatted content.
Non-RDF resource requests are Not Found: we can’t
represent Perl itself!


Introduction
Nodes
Model
Functional
Conclusions

Versioning

Node contents and attributes are versioned.
Links are nodes, so they’re versioned too.
Link embedding/separation and edit-time transclusion
mean one edit may change multiple nodes.
Distinct identities for things like ‘version 3 of text about
Perl’, not ‘version 3 of Perl’.


Introduction
Nodes
Model
Functional
Conclusions

Transclusion

Transclusion link subtype.
Replaces display of source anchor content with target
content.
No part-of relation implied: content operation.
Link embedding/separation leads to edit-time transclusion.


Introduction
Nodes
Model
Functional
Conclusions

Query endpoints

source and target have a range of node identiﬁers.
Not sufﬁcient to represent arbitrary endpoint functions.
sourceQuery and targetQuery have a range of embedded
queries.


Introduction
Nodes
Model
Functional
Conclusions

Generic links

CONTAINS query, which matches on document content.
Implies an anchor at the point of the match when a source.
Matches only the ﬁrst instance, unless transcluding.


Introduction
Nodes
Model
Functional
Conclusions

Parametric nodes

Generalisation of ‘templates’, which are macro
pre-processing.
Instantiate a page with arbitrary key/value pairs.
Range of our links is ‘identiﬁers’, so parameters are part of
the identity of the instantiation.
There is a whole multidimensional space of possible
instances, and each one is a ﬁrst-class object.


Introduction
Nodes
Model
Functional
Conclusions

Parametric node

Template.GoodNode
This node is featured
in topic
param
topic
in particular because
of its
param
virtue


Introduction
Nodes
Model
Functional
Conclusions

Instance space

virtue
_ /

Template.GoodNode Template.GoodNode
{topic→science, {topic→science,
virtue→citations} virtue→grammar}

topic

Template.GoodNode Template.GoodNode
{topic→art, {topic→art,
virtue→citations} virtue→grammar}


Introduction
Nodes
Model
Functional
Conclusions

Adaptive hypermedia

Deliberately couple content with identity
alternateNode for “different node about same thing”
Annotate with information to select upon, e.g. detailLevel
Alternation link subtype selects only one target.


Introduction
Composition
Model
Summary
Conclusions

Outline

1 Introduction
Context

2 Model
Nodes
Functional

3 Conclusions
Composition
Summary


Introduction
Composition
Model
Summary
Conclusions

Desired composition

Haskell
A functional language with lazy
evaluation


Introduction
Composition
Model
Summary
Conclusions

Transclusion of parametric node

FuncTempl {eval→lazy}
A functional lan-
Haskell guage with
_ _ _/
(embedded link) param
eval
evaluation


Introduction
Composition
Model
Summary
Conclusions

Composite document (multiple transclusions)

Haskell
FuncTempl.Pre
(embedded link 1) _ _ _/ A functional lan-
lazy
guage with
(embedded link 2)
NN
NN
NN

FuncTempl.Post
evaluation


Introduction
Composition
Model
Summary
Conclusions

Composite/‘fat’ link (multiple endpoints)

Haskell
FuncTempl.Haskell
(embedded an- _ _ _ _ _ _ _ _ _
(multiple targets)
chor) h h
h h r
h h r
h h r
h h r
th h r
xr
A functional language with lazy evaluation


Introduction
Composition
Model
Summary
Conclusions

Open Semantic Hyperwiki Model

Defines a wiki with open hypermedia features.
First-class links, with edit-time embedding.
Transclusion, including while editing.
Generic and functional links.
Parametric nodes and links.
Full versioning, including links.
Defines how this operates as a semantic wiki.
From hyperlinks to RDF relations.
Prototyped in Weerkat: a highly flexible and modular wiki
system.


Thanks for listening

Questions?


Thanks for listening

Extra slides!


Version identity

Semantic consistency. Content version is not resource version.
All revisions of the Perl node are still about the
same Perl.
Navigational identity. Each version has distinct identity for
linking. Version 3 of the Perl node is Perl3 , not
Perl.meta3 .
Semantic identity. Each version has a distinct URI. (Perl3 .meta,
writtenBy, Phil) means “Phil wrote version 3 of the
content for the Perl node”.


Version identity, cont.

Node title Content URI Represents
Perl Text about Perl Perl Perl itself
Perl3 v3 text re: Perl Perl Perl itself
Perl.meta Text re: t. re: Perl Perl/meta Text re: Perl
Perl.meta4 v4 t. re: t. re: Perl Perl/meta Text re: Perl
Perl3 .meta T. re: v3 t. re: Perl Perl;3/meta v3 t. re: Perl
Perl3 .meta4 v4 t. re: v3 t. re: Perl Perl;3/meta v3 t. re: Perl

Allow version on all non-namespace parts.
Drop the last version to make a URI.


Instance identity

Are two different parameterisations separate SemWeb
resources?
It’s exactly the same as versioning.
Parameter substitution is a content operation, so the tail
parameters don’t change semantic identity.
But Perl {bar→baz}.meta represents the Perl {bar→baz}
instance.


Parametric links

Template.Discussions
type discussion
source param(node).meta
target Discuss.param(node)

If parameters can ﬁll in attribute values, we get parametric
and functional links.
What about a link where both source and target are free
variables?


Eager vs. lazy

When does a parametric instance exist?
Parametric links can potentially affect the hyperdocument
outside of ther immediate content and relations.
Eager: all instances considered to exist.
Lazy: instances exist only if referred to.
Which is most consistent and useful?


Eager vs. lazy, cont.

Lazy: works just like templates. You have to ‘link to’ a
parametric link with some parameters to make it work.
Eager: works like free-variable rules. More consistent, and
more powerful.
Contrary to Semantic MediaWiki, which inherits
templates-as-macro-processing!
Template-macroing links is bad ontology modelling: use
classes.
A ‘Country’ template might have a ‘capital’ parameter.
But templates don’t have capitals!


A Model for Open Semantic Hyperwikis

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