Monkey Business

A challenge by Decision Management Community.

A zoo has four monkeys, during the monkey lunchtime each one ate a different fruit in their favourite resting place. Sam, who doesn’t like bananas, likes sitting on the grass. The monkey who sat on the rock ate the apple. The monkey who ate the pear didn’t sit on the tree branch. Anna sat by the stream but she didn’t eat the pear. Harriet didn’t sit on the tree branch. Mike doesn’t like oranges.

  1. What kind of fruit each monkey ate?
  2. Where their favourite resting place was?

So, how to solve this in SQL? It is easy to identify domains, predicates and rules; after that it is straightforward. Continue reading “Monkey Business”

Eight Years on SO

After eight years on StackOverflow and more than 600 answers, these are my favourite three.

  1. How to understand the fifth normal form? [🔗]
  2. Composite primary key vs. an additional ID column. [🔗]
  3. How to design this database to avoid the cyclic dependency? [🔗]

These are not the highest voted answers, but I like them. All three rely on basic time-tested knowledge and principles, favour simplicity and reasoning over confusion and technical trickery.

Rule 25

Introducing a new tag on the blog named Rule 25. For a post to qualify, the content, knowledge and principles presented must be valid not only today, but were valid at least 25 years ago, and I firmly believe will be valid for at least the next 25 years.
In contrast to current versions of this-and-that, skills and knowledge that do not survive a year.

Murder Mystery

Another fun puzzle, based on the problem No. 55 in [PFJ86] and published as a challenge by Decision Management Community.

Someone in Dreadsbury Mansion killed aunt Agatha. Agatha, the butler, and Charles live in Dreadsbury Mansion, and are the only ones to live there. A killer always hates, and is no richer than his victim. Charles hates no one that Agatha hates. Agatha hates everybody except the butler. The butler hates everyone not richer than aunt Agatha. The butler hates everyone whom Agatha hates. No one hates everyone. Who killed Agatha?

The idea — as in previous posts — is to use concept of predicates, constraints, relations, and Continue reading “Murder Mystery”