1. Semantic and Declarative Technologies AIT Budapest
Péter Szeredi

2. Semantic? Declarative? What the hell…?
According to the Merriam-Webster dictionary:
Semantic (adjective):
relating to the meanings of words and phrases
Declarative (adjective):
having the form of a statement
rather than a question or a command
And in conjunction with technology?
Semantic web:
let search engines understand the web, not just read it
Declarative programming:
solve tasks by just describing the desired solution
Why together in the same course?
Common foundation: (mathematical) logic

3. Question: X? Answer: X?

4. A puzzle scheme from the book …
Imagine an island on which every native is either
a knight – who always tells the truth; or
a knave – who always lies
But they cannot be distinguished otherwise…
If you hear Alf saying: “1+1=2”, he is a …
If you hear Bob saying “1+1=3”, he is a …
What if Cecil says: “I am a knight”?
Can Cecil be a knight? Can he be a knave?
Can it happen that Dan says: “I am a knave”?

5. Puzzle # 28 from the book
In this problem, there are two natives, A and B. A makes the following statement:
“At least one of us is a knave.” (*)
What are A and B?
Think of writing a program in your favorite programming language, which takes (*) or some similar text as input, and returns the solution(s)…

6. Let’s use “controlled English” input
<person> ::= A | B | C | …
<native> ::= knight | knave
<statement> ::= <person> is a <native> |
<person> says <statement> |
<statement> and <statement> |
<statement> or <statement>
“A says: at least one of us is a knave.” becomes:
A says A is a knave or B is a knave
Given this input format, how many lines of code would the puzzle solver require in your favorite programming language?

7. Prolog - Programming in logic (or English?)
Prolog is a simple, yet very flexible programming language based on a subset of First Order Logic
Examples (use syntax extensions, additional operators, etc.)
statements of a knight have truth value 1. % truth(knight, 1).
statements of a knave have truth value 0. % truth(knave, 0).   
statement (Native1 is a Native2) evaluates to B  if 
    statements of a Native1 have truth value B1 and
    statements of a Native2 have truth value B2 and
    B is 1-abs(B1-B2). % is is a built in for arithmetic, here B = 1 iff B1==B2
statement (Native1 says S) evaluates to B  if         
    statements of a Native1 have truth value B1 and 
    statement S evaluates to B2 and B is 1-abs(B1-B2).
statement (S1 or S2) evaluates to B if
    statement S1 evaluates to B1 and 
    statement S2 evaluates to B2 and
    B is B1 \/ B2.  % B is the disjunction of B1 and B2

8. SWISH: a web environment for Prolog

9. Adding constraints to Prolog
Constraint Logic Programming (CLP) – what is it?
It extends Prolog with much stronger reasoning capabilities
for a limited data domain (e.g. integers, Booleans, etc.)
CLPFD (CLP for Finite Domain) – very efficient solution of combinatorial problems, e.g. Sudoku puzzles 7 4 2 1 9 3 5 8 6 7 4 2 1 9 3 5 8 6

10. The Semantic Web (SW) part of the course
Description Logics (DL) – the maths behind SW
DL variants with different complexity
Transforming human knowledge to DL format
Reasoning algorithms (outline)
The practical side of the Semantic Web
OWL 2 (Web Ontology Language)
The Protégé editor and reasoning framework

11. Course summary Rough course layout: Requirements: Course webpage:
Introduction to (First Order) Logic Weeks 1-2
Prolog programming Weeks 2-7
Constraint programming Weeks 8-12
Logics for the Semantic Web Weeks 12-14
Requirements:
2 assignments (15% each) 30% total
2 tests (mid-term & final, 20% each) 40% total
Many small exercises + class activity 30%
Course webpage:

12. Abilities helpful for this course
The ability of clean, logical formulation of one’s expectations of a function or a procedure
The ability to write recursive programs
The acceptance of the single assignment principle: a variable can be assigned a value only once

13. Why should you attend this course?
Learn a very different programming paradigm, which you can also use in other languages such as C, Java, etc.
Learn techniques to quickly and concisely solve difficult algorithmic problems
Learn Description Logics – the maths behind the next generation „intelligent" Web 3.0
It’s a niche market – experts of declarative and semantic technologies enjoy high-paying jobs

14. Some real-life applications
Clarissa: natural voice processing used in systems on the International Space Station
NRM: network management system for configuring multi-vendor IP backbone networks
ContractExpress: intelligent contract creation system for law firms
COPLEX: real-time logistics optimization
Watson: cognitive system that defeated former human champions in the Jeopardy! quiz show
SecuritEase: the dominant stock broking system in New Zealand