Tuesday, February 23, 2016

Final exam grades and exam review

The final exams have been evaluated and the results have been submitted to the examination office.
We offer an exam review on Tuesday, 1 March 2016, morning (09:00 to 12:00) in our office H-1.38.

Thursday, February 4, 2016

Final Exam

Dear students,

we would like to inform you that the final exam will take place:

Friday, 12.02.2016 
10am - 12pm
HS 3

  • the exam time limit is 120 minutes
  • please keep in mind that no additional materials are allowed
  • please formulate your answers in short and precise sentences
  • please write legibly
If you have further questions regarding the final exam, please let us know.

Wir wünschen Ihnen
Viel Erfolg!

Monday, January 25, 2016

Lecture and Lab Course Switched this Week!


Dear students,
Due to travel and project obligations, we have to switch the lecture and the lab course this week (16./27.01.2016).

  • Lecture (originally on Tue, 26.1.2016, 1.30pm) 
    • -> rescheduled to Wed, 27.1.2016, 9.15 am
  • Lab Course (originally on Wed, 27.1.2016, 9.15am) 
    • -> rescheduled to TUE, 28.1.2016, 1.30 pm
Thanks a lot for your consideration.

Wednesday, January 13, 2016

Ontology Evaluation

via http://www.gocomics.com/calvinandhobbes/
It is essential to ensure the quality of the ontology that you are going to develop. Simply for reasons of efficiency with respect to further refinement or additions. When working and discussing the examples with OntoClean in the lecture and the lab course, you have realized that it is important to have clear definitions of your concepts/classes. In our examples, we have treated the discussed ontologies always as rather general upper ontologies with the aim to represent the 'real' world in its entirety...and as you might have noticed, this sometimes is more or less futile since we were not able to reach an agreement upon the interpretation of the represented classes.

Therefore, in real life applications of ontology engineering, always keep in mind the purpose of your ontology, the application for which the ontology is intended to be used. Keep your knowledge representations restricted to the intended purpose. If your application demands countries to be treated simply as geographical entities, you don't have to consider the administrative or legal structure of a country for your application. Thus, it should also not be necessarily considered in your knowledge representation -- or also in your evaluation.

The OntoClean methodology focusses on the taxonomic structure of an ontology, where the suborder relation is considered being a formal subsumption. Strictly speaking, if an individual is member of a class, it is necessarily also a member of the according superclass. To check the semantical consistency of your class taxonomy, all the classes are tagged with metaproperties (Rigidity, Unity, Identity, and Dependency). It is crucial that your metaproperties clearly reflect the intended meaning of the classes. If in doubt, always give an explanation/justification, why you have chosen a specific metaproperty. Then, you look for violations of the given OntoClean constraints for these metaproperties. Whenever you find a constraint violation, this is an indication either to change your ontology or to reconsider the definition (the meaning) of your ontology classes accordingly.

One comment on the exercise in the lab course today:
We should label the owl:Thing (the top concept in the DBpedia Ontology) with -U, since the instances of owl:Thing do not have a common unity criterium. Possibly there are also some classes subsumed by owl:Thing that contain entities which are not necessarily considered a whole, i.e. which must have the meta-property ~U (anti-Unity), but this cannot be assumed for all the individuals of owl:Thing alike (and also for entity in the example from the slides, lecture 5.8). Instead, we have to choose the more general -U (no common unity criterium) for owl:Thing here. 

Thanks a lot for pointing this out to me at the end of the lab course!!!  

Wednesday, December 16, 2015

Protégé - Example Ontology file

Please find the Example Ontology file, we created in the lab course for the exercise Modelling the Facts in Protégé from exercise sheet 7.

You can find the same in the material folder as well.

Atoms, Atomic Formulas, and Functions

 © 2015 by Sidney Harris
Thanks again for pointing out ambiguities and lacks of clarity in the lecture material!

In the lab course today, we were discussing atoms vs. atomic formulas in FOL.

Usually, atoms and atomic formulas are used equivalently in FOL to denote formulas that contain no logical connectives and quantifiers, or equivalently, formulas that do not contain any strict subformulas. Atoms (atomic formulas) are the simplest well-formed formulas in FOL.

For example, consider the following (composite) formula:
∀x. P (x) ∧ ∃y. Q (y, f (x)) ∨ ∃z. R (z)

where x,y,z denote variables, f denotes a function symbol, and P, Q, R denote predicates.

The atoms (atomic formulas) contained in this formula are:
  • P (x) 
  • Q (y, f (x))
  • R (z)
In the lecture slides, we only gave a brief summary for the definition of FOL based on examples. For an extensive definition of FOL, please refer to [1].

Thus, whenever we are talking about atoms, as e.g. when we were talking about rules, we refer to atomic formulas.

Then there was the question, whether a function like e.g. mother(x) is an atom/atomic formula?

The definition of an FOL formula says:
  1. If P is a predicate symbol of arity k, and if t1,...,tk, are terms, then P(t1,...,tk) is a formula.
  2. (Negation) For all formulas F, also ¬F is a formula
  3. (Binary Connectives) For all Formulas F,G, also F∧G,F∨G,F→ G,F↔G are formulas 
  4. (Quantifiers) If x is a variable and F is a formula, then also ∀x.F and ∃x.F are formulas
A function alone is only considered a term, following the definition of an FOL term:
  1. all variables are terms
  2. If f is a function symbol of arity k, and if t1,...,tk, are terms, then f(t1,...,tk) is also a term.
For a distinction, you may keep in mind that terms do not compute a truth value, a formula does.

References:
[1] Uwe Schöning: Logik für Informatiker. Spektrum Akademischer Verlag, 2000
or in english:
[2] Uwe Schöning: Logic for computer scientists, Birkhäuser, 2008, also online availabl

Tuesday, December 8, 2015

Final Exam

The final exam will take place on
Friday, February 12, 2016 – 10:00 AM to 12:00 PM

The location will be announced.