## Reindeer Ordering

The Decision Management Community posted a fun challenge: Santa’s elves are supposed to order nine reindeer according to a set of rules. The rules are:

1. Comet behind Rudolph, Prancer, and Cupid.
2. Blitzen behind Cupid.
3. Blitzen in front of Donder, Vixen, and Dancer.
4. Cupid in front of Comet, Blitzen, and Vixen.
5. Donder behind Vixen, Dasher, and Prancer.
6. Rudolph behind Prancer.
7. Rudolph in front of Donder, Dancer, and Dasher.
8. Vixen in front of Dancer and Comet.
9. Dancer behind Donder, Rudolph, and Blitzen.
10. Prancer in front of Cupid, Donder, and Blitzen.
11. Dasher behind Prancer.
12. Dasher in front of Vixen, Dancer, and Blitzen.
13. Donder behind Comet and Cupid.
14. Cupid in front of Rudolph and Dancer.
15. Vixen behind Rudolph, Prancer, and Dasher.

The challenge is to create a decision model, but Continue reading “Reindeer Ordering”

## Eight Queens in SQL [4]

This is the fourth and final part of the series showing how to solve the “Eight Queens” chess puzzle, using a database design and SQL. The main idea is to design using natural language and concepts of domains, predicates, constraints, sets, set operations, and relations.

Links to all previous and this post’s code.
Part Main Topic Code (pgSQL)
1 Domains, Types part 1
2 Predicates, Constraints, Relations part 2
3 Propositions and Facts part 3
4 The Algorithm and the Solution part 4

### Algorithm

Say we place a queen, Q1, on square c5, Continue reading “Eight Queens in SQL [4]”

## Eight Queens in SQL [3]

The third article in the series.

Links to all previous and this post’s code.
Part Main Topic Code (pgSQL)
1 Domains, Types part 1
2 Predicates, Constraints, Relations part 2
3 Propositions and Facts part 3

### Relation Values

To populate tables simply run the code; it is self explanatory. You may want to keep an eye on the model while reading the code.

### Propositions and Facts

A proposition is a declarative sentence, Continue reading “Eight Queens in SQL [3]”

## Eight Queens in SQL [2]

This is the second article in the series; the previous one introduced the problem and specified domains.

Links to all previous and this post’s code.
Part Main Topic Code (pgSQL)
1 Domains, Types part 1
2 Predicates, Constraints, Relations part 2

### The Essence

The idea is to describe the problem using natural language and concepts of domains, predicates, constraints, relations and keys; here are a few simple rules to keep in mind.

###### From predicates and constraints to relations and keys
• A predicate variable — from a specific domain — maps to an attribute of the relation.
• Internal (to predicate) uniqueness constraints map to keys of the relation.
• External (to predicate) inclusion constraints map to foreign keys between two relations.
• A predicate and the matching relation represent — evaluate to — a set of facts about the universe of discourse (the problem).
• A predicate and the matching relation should not be separated, otherwise information will be lost, for all practical purposes.