The language department in None University wants to build a language learning

platform for their students. Furthermore, they have chosen you as their database

designer. The first step is to create an ER$-$diagram. These are their requirements:

A$.$ The database must keep track of all languages that are taught on the platform. It

should store their ID$,$ name, and the number of native speakers in the world.

B$.$ The platform hosts language courses. Courses have an ID$,$ name, start date and

a difficulty level. Each course covers a single language but there can be multiple

courses covering the same language.

C$.$ To use the platform, one must sign up as a subscriber. Each subscriber has an

ID and their name, unique username and unique email are also stored. All subscribers

are teachers and$/$or learners. For learners, their last login date is stored as well as

experience points $($XP$)$ that they can collect on the platform.

D$.$For teachers, their unique phone numbers are stored, as well as their office

hours. Their bank account number is also stored $($divided into bank, ledger, and

account number$).$ Courses are taught by a single teacher, but a teacher teaches one or

more courses.

E$.$ Learners can be registered to courses. Courses are cancelled if fewer than $10$

learners sign up$.$ Moreover, learners can review teachers, regardless of whether they

are registered to a course of theirs. However, since the same subscriber can be a

teacher and learner, it is important that learners cannot review themselves as teachers.

In each review, the learner gives stars from $1$ to $5.$ A single learner can review the

same teacher multiple times.

F$.$Each course has at least one milestone. Milestones have IDs and credits.

Learners make progress in the courses that they are registered to by completing the

milestones within it$.$ When a learner completes a milestone, their grade is stored.

G$.$Milestones can stand alone $($such as reading material, etc.$),$ but they can also be

divided into either Assignments or Exams. Assignments have a due date, and exams

have a date and duration.

H$.$Exams can be partitioned into one or more questions. Each question in an exam

is identified with its number on the exam. The questions$$ text and weights are also

stored.

I. Learners can follow each other on the platform. Learners may be part of squads

for studying together or socializing. Each squad has an ID$,$ a name, and an optional

address of their meeting point. Of course, a squad is not a squad if it has no members!

Squads can be associated to a specific language but that is not a requirement.

J$.$Furthermore, the university has decided that teachers may nominate selected

learners and squads for sponsorship. These sponsees must be kept track of$.$ Sponsees

have an ID and the grant amount they receive is also stored. A teacher may nominate

the same learner$/$squad multiple times, but only once per year.