Uni Göttingen
Institute for Informatics
Databases and Information Systems

dbis

Deductive Databases
Summer 2021

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

Date and Time:

  • Monday 10-12 IFI SR 2.101 and Tuesday 14-16 IFI SR -1.101.
  • 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. Maybe, there are also optional meetings in presence at the IFI.
  • 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 from the continuation of the Databases lecture slide set
  • 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".
If (and as long as) non-german-speaking participants attend, the course will be given in english.

Module CS.M.inf.1241:
The module's home is the MSc studies in Applied CS. It can also be credited in the BSc studies in Applied CS, and in several other studies:
6 ECTS credits (Studies in Applied Informatics and in MSc Wirtschaftsinformatik),
Maths (Dipl, MSc), Teaching, Magister, PhD GAUSS, ...

Note: participants are required to have successfully attended the module Databases or an equivalent module.

Enrolment: there is no official enrollment for DBT. Students may freely decide to attend the lecture. Only at the end, for the exams, there is a registration (with FlexNever).
DBIS does not use StudIP for uploading materials. You find all relevant information about the lecture at this Website.

Course Description

The course combines theoretical aspects with their applications in deductive databases and knowledge representation:

  • First-Order Logic
  • The first-oder-logic-based twin to the relational algebra: Relational Calculus; domain-independence, safeness; translation of queries between Algebra and Calculus
  • Model Theory, Reasoning and Query Answering in First-Order Logic: Resolution and Tableau Calculus
  • Conjunctive queries (Datalog queries)
  • Deductive Databases - Positive Recursive Datalog
  • Advanced Datalog: Datalog with Negation, Well-Founded Semantics, Stable Semantics, Answer Set Programming (ASP).
  • Practical Exercises will be done with XSB Prolog/Datalog and smodels.
  • The running example is the "Mondial" database. SQL queries against Mondial can be stated via a Web interface.
  • On a higher level, students will gain some insights into (commonsense) reasoning and about the intuitive background of formal logical frameworks.
  • Example for reasoning: Fish Puzzle:
    First step: find a solution (by human reasoning). This will finally be solved by ASP.

Dates & Topics

  • Mon 12.4. No lecture. There is the institute's MSc welcome meeting in the afternoon.
  • Tue 13.4. and Mon 19.4.: No DD meetings
  • Tue 20.4.: live meeting via StudIP->Meetings->DD-2021-04-20
    Administrativa, Overview, Introduction
    Material for Self-studying:

Part I: Logic-Based Database Theory: Relational Calculus

Part II: Positive and Stratified Datalog

Part III: Well-Founded and Stable Models, Answer Set Programming

Exams

  • With this year, we try a modified strategy for oral exams:
    Oral exams, basically whenever needed:
  • Exam procedure (as before): about 30-40 minutes. Candidates start with talking about a topic of their choice (5-10 minutes), then questions+answers, including sketches on paper develops dynamically.
    Languages: German, English.
  • 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.)

Resources

  • All slides of DBIS lectures can be found here.
  • Some topics of the course are closely related to chapters of the book Foundations of Databases by Serge Abiteboul, Richard Hull, and Victor Vianu that can be found as pdf here.
  • A comprehensive course in logics (incl. slides and a skriptum) (in German) can be found at Formale Systeme, Prof. Dr. P.H.Schmitt, Karlsruhe (mainly Chapters 4 und 5).

Software/Playground

  • SQL-Queries on the Mondial database can be stated via this web form.
  • Mondial in Datalog is available here.
  • The Datalog sample programs from the slides are available here.
  • For experimenting with Datalog, the XSB system is installed in the IFI CIP-Pool:
    Add 
       alias xsb='rlwrap ~dbis/LP-Tools/XSB/bin/xsb'
    to your ~/.bashrc and then source .bashrc. Go to the directory where your input sources (e.g. mondial.P from above) is located and call 
     may@pc01> xsb
    The xsb prompt is then ?- .
    To leave XSB, press CTRL-D.
    Enter 
     ?- [mondial].
    to "load" mondial into XSB (The file mondial.P must be in the current directory). Query with e.g. 
     ?- country(A,B,C,D,E,F).
    returns the first answer. Press "return" once to leave answers, press any other key and "return" to get next answer.
    Some usage hints:
    • String constants are enclosed in single quotes (like in SQL): ?- city('Berlin',C,P,Pop,_,_,_).
      Double quotes are not allowed.
    • ?- city(N,C,P,Pop,_,_,_), Pop > 1000000 . ... complains about "Wrong domain in evaluable function compare-operator/2."
      There is no SQL-style NULL in Datalog. Instead we use the constant null; this breaks the domain for numerical comparison. So check first that P is not null (unequality can be written as "x \= y" or "not (x=y)" in Prolog):
      ?- city(N,C,P,Pop,_,_,_), Pop \= null, Pop > 1000000 .
      ?- city(N,C,P,Pop,_,_,_), not (Pop = null), Pop > 1000000 .
  • Download of XSB Prolog/Datalog from Stony Brook University.
  • For experimenting with stable models, smodels and its lparse frontend are installed in the CIP pool:
    Add 
       alias smodels='~dbis/LP-Tools/smodels-2.34/smodels'
   alias lparse='~dbis/LP-Tools/lparsebin/lparse'
    to your ~/.bashrc and then source .bashrc. Then call 
     may@pc01>  lparse -n 0 porq.s|smodels
 may@pc01>  lparse -n 0 -d none winmove.s|smodels
 may@pc01>  lparse -n 0 -d none --partial winmove.s|smodels
    where -n 0 indicates to show all stable models (any number can be given 0 means "all"; default is 1, then, it stops after returning the first stable model!). Option -d none omits the EDB predicates from the models. Option --partial also outputs the partial stable models, where an output of p'(...) then means that p(...) is a least undefined.
    See lparse -help and smodels -help for further options.
  • Download smodels and lparse from Helsinki University of Technology.
    • gunzip both, unpack with tar xvf.
    • cd into smodels-X.YZ, run make, creates smodels binary.
      Assign an alias for calling it.
    • cd into lparse-X.Y.Z, edit INSTALLATION_PATH in Makefile, read INSTALL text, and do what is recommended.
      Assign an alias for calling it.