Institute for Informatics
Georg-August-Universität Göttingen

Databases and Information Systems

dbis
Uni Göttingen

Semantic Web
WS 2020/21

Prof. Dr. Wolfgang May,
Lars Runge, M.Sc., Sebastian Schrage, M.Sc.

  • Date and Time: Tue 14-16, Wed 10-12
  • Room: IFI 2.101 (North Campus)
  • Virtual Meetings: We will use BigBlueButton provided by GWDG; the rooms/meetings can be entered via StudIP. There also the recordings can be found (they cannot be exported or edited at all)
    Please also read the general and technical information about DBIS virtual teaching.

Exercises (Übung): integrated into lecture (see announcements on this page). There will be non-mandatory exercise sheets whose solutions will be discussed as parts of the lecture.
All materials and announcements can be found HERE on the "blue DBIS pages"

Technical Data: 4 SWS, 6 ECTS credits (Studies in Applied Informatics).
The module's home is the MSc studies in Applied CS. It can also be credited in the BSc studies in Applied CS (as "Vertiefung Softwaresysteme und Daten"),
and in several other studies:
BSc/MSc Wirtschaftsinformatik, Mathematik (BSc/MSc), Teaching/2-Fach-Bachelor, PhD GAUSS, ...

Prerequisites

  • Knowledge in First-Order Logic as taught in "Formale Systeme" is sufficient. Although, prospective participants are recommended to have participated in the lecture Deductive Databases.
  • XML: RDF/XML uses XML as representation, but requires only a little bit of knowledge about XML. A short introduction to XML from that point of view will be given in the lecture.
    XML with DTD, XPath, XQuery, XSLT and XML Schema is the topic of the lecture Semistructured Data and XML (prospectively taking place again in Summer Term 2021).

Course Description

  • Short Review: Basic Notions of First-Order Logic
  • RDF: N3 and RDF/XML format, semantics
  • SPARQL: the query language for RDF data
  • Linked Open Data (LOD): Web of Data and distributed querying.
  • The Mondial database is used as an example for RDF data.
    Mondial LOD entry point.
  • RDFS, OWL: having RDF data with additional reasoning
  • Description Logics: the logic underlying OWL
  • Practical experiments with RDF, Jena, Reasoners etc.
  • An experimental Web interface can be found for RDF+OWL and SPARQL here

Dates & Topics

  • First Meeting: Tue 3.11. (note that WS lectures start only on 2.11.!) 14-16: Administrativa, Overview. Slides: Introduction and Ontologies
  • Reasoning Motivation: the Einstein/Fish Puzzle ... will (again) be solved declaratively, but totally different than in the "Deductive Databases" lecture.
  • ... to be extended ...

The SmartBoard Notes are collected here (only relevant ones, so for some dates there are no notes).

The complete slide set can be found here (including the Semantic Web Lab Course Slides). The slides of the SSD&XML lecture can also be found there. Knowledge of XML is only required so far as RDF/XML is (in addition to the N3 format) a possible representation of RDF data. One should be able to "understand" an XML document. XPath/XQuery and XSLT are not required.

Exams

  • Oral exams, several slots to choose between February 15th and April 2021.

Background Literature

P. Hitzler, M. Krötzsch, S. Rudolph, Y. Sure: "Semantic Web - Grundlagen" (in German). Springer eXamen.press, 2008; ISBN 978-3-540-33994-6.
The (german language) book covers nearly exactly the contents of the lecture and also contains an introduction to first-order logic in the appendix.

P. Hitzler, M. Krötzsch, S. Rudolph, Y. Sure: "Foundations of Semantic Web Technologies" (in English). Chapman & Hall/CRC, 2009; ISBN: 9781420090505
The (english language) book covers nearly exactly the contents of the lecture and also contains an introduction to first-order logic in the appendix.

For the part on (first order) logic, and textbook on foundations of logic from the library (e.g. "Logik für Informatiker" (in German) von Uwe Schöning) or the manuscript "Formale Systeme" by Peter H. Schmitt (Uni Karlsruhe) (Kap. 1-5) can be used.

Some Links


Semantic Web Tools and Links

If you experience any problems (forgotten chmod, wrong paths, forgotten updates etc.), please notify us.

Web-wide Services

Professional Tools

Jena: RDF and SPARQL

Apache JENA ( https://jena.apache.org/ ) is a free and open source Java framework for building Semantic Web and Linked Data applications.
The course uses a lightweight housemade shell interface to Jena for querying:

  • Download most recent version (incl. OWL2, partially SPARQL 1.1, based on Jena 2.10 and compatible Openllet) Nov. 2019.
  • in the CIP Pool located at /afs/informatik.uni-goettingen.de/course/semweb-lecture/JENA-API/semweb.jar
  • Experimental Web interface

  • set alias (bashrc etc.)
     alias jena='java -jar /afs/informatik.uni-goettingen.de/course/semweb-lecture/JENA-API/semweb.jar'
  • query: (if=input-files, qf=query-file, e.g. in SPARQL)
    jena -q -if inputfiles -qf queryfile
  • general options:
    -il: input language (allows RDF/XML RDF/XML-ABBREV N-TRIPLE N3 TURTLE; N3 is default)
    -if: input files
  • query options:
    -q: query
    -il, -if: as above
    -qf: query-file
  • transform options:
    -t: transform
    -ol: output format (allows RDF/XML RDF/XML-ABBREV N-TRIPLE N3-PLAIN N3-PP N3-TRIPLE N3 TURTLE; N3 is default)
  • export class tree; options:
    -e: export class tree (gives some insight for debugging an ontology ...)
    -il, -if: as above
  • reasoner options (for -q and -e):
    activate reasoning; default: internal reasoner: option -inf (for "inference")
    or use the pellet class that comes with the semweb.jar:
     jena -q -inf -qf query-filename
     jena -q -pellet -qf query-filename

Pellet - the OWL Reasoner

  • Openllet Homepage (Open Source tool based on the last freely-available version of Pellet)
  • Pellet itself has been turned into a commercial product at Stardog.

LOD: Accessing RDF Data in the Web

  • rapper: a tool that accesses a Web page in RDF-reading mode to get RDF triples: e.g.
    rapper http://sws.geonames.org/3017382/

Mondial in RDF

The Mondial database in RDF format can be found at http://www.dbis.informatik.uni-goettingen.de/Mondial/#RDF.

Call e.g.

 jena -q -qf mondial-query.sparql
or
 jena -pellet -q -qf mondial-meta-query.sparql

Usage in the CIP Pool

From the CIP Pool computers at the IFI (ground floor or log in from remote), the software and resources are directly accessible:

  • log in from remote to login.stud.informatik.uni-goettingen.de (Linux: ssh, Windows: puTTY)
  • log through to one of the individual computers (e.g. ssh c032)
  • set the alias in your .bashrc file:
     alias jena='java -jar /afs/informatik.uni-goettingen.de/course/semweb-lecture/JENA-API/semweb.jar'
  • The lecture's RDF directory with the n3 files can be found at
     /afs/informatik.uni-goettingen.de/user/d/dbisuser/public_html/teaching/SemWeb/RDF
  • The Mondial files can be found at
     /afs/informatik.uni-goettingen.de/user/d/dbisuser/public_html/Mondial
     /afs/informatik.uni-goettingen.de/user/d/dbisuser/public_html/Mondial/Mondial-RDF