Decision models (like databases) are frequently deal with analysis of collections of objects. This month Challenge deals with such situation: you need to help an HR office create a rules-based service to analyze its employees. Each employee  has a unique name,  age, gender, marital status, locations (places of residence), number of children, salary, and more attributes. This information is coming to the service as a JSON request such as in this file. Your service should find answers to questions such as:

• What is an average salary? What is the maximal and minimal salaries?
• How many employees are single?
• In which states do the employee have residences?
• How many people are inside 20% of the highest paid  employees? List these high-paid employees.