Challenge: “a test of one’s abilities or resources in a demanding but stimulating undertaking” — The free English dictionary 

• CH1: Polyglot meets Xperanto [here]
• CH-2: More intensive summarization: choose one of the following
  1. Median and standard deviation [ pdf ]
  2. Inverted index summarizations [ pdf ]
• CH-3 Filtering patterns: choose one of the following
  1. Bloom [ pdf ]
  2. Top ten [ pdf ]
• CH-4: Join patterns: choose two of the following
  1. Reduce side join classic and with bloom filter [ pdf ]
  2. Replicated join [ pdf ]
  3. Composite join [ pdf ]
  4. Cartesian product [ pdf ]