The history of the Semantic Web goes back to several years now
It is worth looking at what has been achieved, where we are, and where we might be going…
Let us look at some results first!
The basics: RDF(S)
We have a solid specification since 2004: well defined (formal) semantics, clear RDF/XML syntax
Lots of tools are available. Are listed on W3C’s wiki:
RDF programming environment for 14+ languages, including C, C++, Python, Java,
Javascript, Ruby, PHP,… (no Cobol or Ada yet !)
13+ Triple Stores, ie, database systems to store (sometimes huge!) datasets
etc
Some of the tools are Open Source, some are not; some are very mature, some
are not :
it is the usual picture of software tools, nothing special any more!
Anybody can start developing RDF-based applications today
The basics: RDF(S) (cont.)
There are lots of tutorials, overviews, and books around
again, some of them good, some of them bad, just as with any other areas…
Active developers’ communities
Large datasets are accumulating. E.g.:
IngentaConnect bibliographic metadata storage: over 200 million triplets
New issues may pop up at the last moment via reviews
a query language needs very precise semantics and that is not that easy
Some features are missing
query on list/sequence/set membership
control and/or description on the entailment regimes of the triple store (RDFS? OWL-DL? OWL-Lite? …)
modify the triple store
…
postponed to a next version…
Of course, not everything is so rosy…
There are a number of issues, problems
how to get RDF data
missing functionalities: rules, “light” ontologies, fuzzy reasoning, necessity to review RDF and OWL, …
misconceptions, messaging problems
need for more applications, deployment, acceptance
etc
How to get RDF data?
Of course, one could create RDF data manually…
… but that is unrealistic on a large scale
Goal is to generate RDF data automatically when possible and “fill in” by hand only when necessary
Data may be around already…
Part of the (meta)data information is present in tools … but thrown away at output
e.g., a business chart can be generated by a tool: it “knows” the structure, the
classification, etc. of the chart, but, usually, this information is lost
storing it in web data would be easy!
“SW-aware” tools are around (even if you do not know it…), though more would be good:
Photoshop CS stores metadata in RDF in, say, jpg files (using
XMP)
RSS 1.0 feeds are
generated by (almost) all blogging systems (a huge amount of RDF data!)
…
Data may be extracted (a.k.a. “scraped”)
Different tools, services, etc, come around every day:
May be considered as an alternative serialization of (part of) RDF; may be bound to GRDDL in practice
RDFa example
For example
<div about="http://uri.to.newsitem">
<span property="dc:date">March 23, 2004</span>
<span property="dc:title">Rollers hit casino for £1.3m</span>
By <span property="dc:creator">Steve Bird</span>. See
<a href="http://www.a.b.c/d.avi" rel="dcmtype:MovingImage">
also video footage</a>…
</div>
yields, by running the file through a processor:
<http://uri.to.newsitem>
dc:date "March 23, 2004";
dc:title "Rollers hit casino for £1.3m;
dc:creator "Steve Bird";
dcmtype:MovingImage <http://www.a.b.c/d.avi>.
Linking to SQL
A huge amount of data in Relational Databases
Although tools exist, it is not feasible to convert that data into RDF
Instead: SQL ⇋ RDF “bridges” are being developed:
a query to RDF data is transformed into SQL on-the-fly
the modalities are governed by small, local ontologies or rules
An active area of development, on the radar screen of W3C!
SPARQL as a unifying point?
Missing features, functionalities…
Everybody has a favorite item, ie, the list tends to infinite…
W3C is a standardization body, and has to look at where a consensus can be found
Rules
OWL-DL and OWL-Lite are based on Description Logic
There are things that DL cannot express
(though there are things that are difficult to express with rules and easy in DL…)
A well known examples is Horn rules (eg, the “uncle” relationship):
(P1 ∧ P2 ∧ …) → C
e.g.: for any «X», «Y» and «Z»: “if «Y» is a
parent of «X», and «Z» is a brother of «Y» then «Z» is the
uncle of «X»”
Negotiate eBusiness contracts across platforms: supply
vendor-neutral representation of your business rules so that others
may find you
Describe privacy requirements and policies, and let clients
“merge” those (e.g., when paying with a credit card)
Medical decision support, combining rules on diagnoses, drug
prescription conditions, etc,
Extend OWL with rule-based statements (e.g., the uncle example)
But: it is not easy!
From a theoretical viewpoint, Description Logic and Logic Programming are different:
DL is based on FOL Model Theory, while LP not exactly
Open vs. Closed Worlds, monotonicity vs. non-monotonicity: OWL operates on an Open World, Rules usually don’t
…hence it is not easy to combine these
Rule systems often operate with procedural rules (“execute this and this Java procedure if…”)
Rules Interchange Format Working Group
The W3C Working Group started at the beginning of November 2005
Work is planned in two “phases”:
construct an extensible format for rule interchange with simple rule systems
define more complex extensions
Great interest from financial services, business rules, life science community, …
Work is going on!
“Light” ontologies
For a number of applications RDFS is not enough, but even OWL Lite is too much
OWL-Lite needs a DL reasoner to operate properly
There may be a need for a “light” version of OWL, just a few extra possibilities v.a.v. RDFS
There are a number of proposals, papers, prototypes around: RDFS++, OWL Feather, pD*, …
pD*, for example, has property characterization (symmetric, transitive, inverse),
class and property equivalence, and property restrictions with some or all values
This might consolidate in the coming years
Revisions of RDF and OWL?
Such specifications have their own life
Missing features come up, errors show up
There will probably be a next version at some point
Revision of the RDF model?
Some restrictions in RDF may be unnecessary (bNodes as predicates, literals as subject, …)
Issue of “named graph”: possibility to give a URI to a set of triplets and make statements on those
Syntax issues in RDF/XML (eg, QNames in properties)
Alternative XML serializations?
Add a time tag to statements? A probability value? A measure of “fuzzyness”?
Internationalization issues with literals (how do I set “bidi” writing?)
These are just ideas floating around…
Revision of OWL? (OWL 1.1)
There is a group working on this (outside W3C for now)
not a scientific conference, but commercial people making real money!
speakers in 2006: from IBM, Cisco, BellSouth, GE, Walt Disney, Nokia, Oracle, …
not all referring to Semantic Web (eg, RDF, OWL, …) but semantics in general
but they might come around!
Major companies offer (or will offer) Semantic Web tools or systems using Semantic
Web: Adobe, Oracle, IBM, HP, Software AG, WebMethods, Northrop Gruman, Altova, …
“Corporate Semantic Web” listed as major technology by Gartner in 2006
Applications are not always very complex…
Eg: simple semantic annotations of patients’ data greatly enhances communications among doctors
What is needed: some simple ontologies, an RDFa/microformat type editing environment
Simple but powerful!
Data integration
Data integration comes to the fore as one of the SW Application areas
Very important for large application areas (life sciences, energy sector, eGovernment, financial institutions),
as well as everyday applications (eg, reconciliation of calendar data)
Life sciences example:
data in different labs…
data aimed at scientists, managers, clinical trial participants…
large scale public ontologies (genes, proteins, antibodies, …)
different formats (databases, spreadsheets, XML data, XHTML pages)
etc
Life Sciences (cont.)
General approach
Map the various data onto RDF
assign URI-s to your data
“mapping” may mean on-the-fly SPARQL to SQL conversion, “scraping”, etc
Merge the resulting RDF graphs (with a possible help of ontologies, rules, etc, to combine the terms)
Start making queries on the whole!
Remember the role of SPARQL?
Example: antibodies demo
Scenario: find the known antibodies for a protein in a specific species
State of the Semantic Web
!)
:
it is the usual picture of software tools, nothing special any more!
