Q$3.(25$ pts$.)$ Using the following information, draw an ER diagram. Be sure to indicate the various attributes of each entity and relationship set; also specify the necessary key and participation constraints for the relationship sets.

Doctors of the World $($DW$)$ is an international organization dedicated to implement health care plans in poor countries. DW needs to design a database to record information to fulfill the following specifications:

Doctors are identified by their id$.$ It is required for each doctor to record her$/$his name, birthday, country of citizenship and sex.

A doctor has always at least one medical specialty. A medical specialty is identified by a code and has a name.

The doctors are ranked in each of her$/$his specialties according to their years of experience in that specialty.

The organization collaborates with international agencies to implement and deploy health plans in some countries. Each international agency is identified by an id and has a name. Countries are identified by their names. For each country, its population and its poverty index must be also stored.

Each health plan is implemented in a given country, and the name of the health plan is uniquely associated among the health plans of that country. Each health plan has a budget and is carried out during a period of time. A health plan is always sponsored by one or more international agencies. Each international agency provides part of the budget of the health plan. The total budget provided by the agencies is never less than the health plan budget.

A country attended by the organization needs some medical specialties. A health plan designed for a given country covers some of its needs for medical specialties.

A doctor may participate in several health plans. The period of time that a doctor participates in a health plan must be recorded. A doctor cannot participate in two health plans simultaneously. A doctor never participates in a health plan more than once. The participation of a doctor in a health plan never exceeds the duration of the plan.

Each health plan includes at least $7$ doctors; one of who is the coordinator of the health plan. The coordinator of the plan always works for during the duration of the plan. A doctor involved in a health plan must have one of the specialties required by the health plan.