Institute for Informatics
Georg-August-Universität Göttingen

Databases and Information Systems

dbis
Uni Göttingen

Semantic Web
WS 2021/22

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)
  • This year, DBIS will use mainly non-live teaching by pre-recordings. There will be some live online meetings with BigBlueButton provided by GWDG; the rooms/meetings can be entered via StudIP.
  • Materials for self-studying (in english) will be linked below weekwise:
    • revised videos taken from summer term 2020 (as the "original" dates in the filenames indicate),
    • PDF slides
  • Please also read the general and technical information about DBIS virtual teaching.

Lecture and Exercises mixed (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 Datenbanken"),
and in several other studies:
BSc/MSc Wirtschaftsinformatik, Mathematics (BSc/MSc), Digital Humanities, Teaching/2-Fach-Bachelor, PhD GAUSS, ...

Prerequisites

  • Basic knowledge of databases (conceptual modeling, relational model, SQL), background notions of "data model" in general, the idea of declarative set-oriented query languages.
  • Knowledge in First-Order Logic as taught in "Formale Systeme" is recommended; at least you should have some idea of it, and not be scared of formalisms. Semantic Web is an example of applied First-Order Logic and model theory.
    There is also the "sibling" lecture Deductive Databases that is also applied First-Order Logic, but with a slightly different model theory.
  • 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 2022).

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

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 14th and April 2022.
  • Exam procedure: about 30-40 minutes, most probably online . Candidates start with talking about a topic of their choice from the lecture (5-10 minutes), then questions+answers, including sketches on paper develops dynamically. The 5-10 minutes talk at the beginning should give me as an examiner a good impression of your knowledge, and a good starting point to assess your knowledge with further questions (usually starting with the chosen topic, and then also going to other topics from the lecture).
    Languages in oral exams: English and/or German.
  • With this year, we try a modified strategy for oral exams:
    Oral exams, basically whenever needed:
    • Registration via FlexNow:
      • The exam regulations (Allgemeine Prüfungsordnung BSc/MSc Göttingen (2013), Par.10b) and the FlexNow system (that we must use) are not very appropriate for administrating flexible individual oral exams. We solve this as follows:
      • Oral exams and the formal registration in FlexNow are "always" possible, this means, also during semesters where the lecture does not take place.
      • Deregistration in FlexNow is not possible. So register in FlexNow only when you are sure that you want to do the exam. You must be registered when actually doing the exam.
      • The "FlexNow Exam" for summer term lectures is thus configured as follows: Registration between Jul 1st and Jan 31st (De-registration until Jul 1st, means "not possible"). If you want to do the exam later, use the subsequent winter term exam (always Feb 1st - Jun 30th).
    • For your actual individual exam appointment, contact may at informatik.uni-goettingen.de for a concrete appointment, usually 3-4 weeks before the exam, specifying which week and maybe even what day you prefer and morning/afternoon.
      (We will become aware of your registration only via this mail - FlexNow does not notify us about incoming registrations - and usually, we do not look inside it actively.)

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