Algorithm for appointment reminders

algorithmsmultithreadingschedulingsms

My program allows users to store appointments in a calendar. What has been requested of me is the ability for SMS reminders to be sent to people to remind them of their appointment. The SMS would need to be sent out about 2 days prior to their appointment.

I thought the best way to achieve this is to choose a time of the day (eg. midday) for the software to check to see which appointments are in 2 days time and then send out the SMS reminders to the people who have those appointments.

Would this be an advisable approach to this problem? Is it advisable to have this happen at one time of the day, or would it be better to somehow spread it out over a longer time?

I am assuming at this point that a background thread would be a good idea for this type of activity.

Best Answer

This Question should be proposed to the user, as the ramifications to the user far out way the technical concerns.

The frequency that you call your process should have very little baring on the design.

Data Model

User - The abstraction of your user:

UserId
TimeZone

Appointment - A scheduled appointment:

AppointmentId
UserId
DateRange (5 minutes starting at a UTC timestamp)

Day - Borrowing heavily from your answer Rachel, this object will be a derived list of all appointments for a single Day...

BUT... The idea of a single Day is a floating concept. Depending on what TimeZone the user is coming from then one persons Day may overlap another persons Day, therefore Day is relative to a users Timezone, and thus the DateRanges in the Appointments for that Day could be completely different depending on what Timezone we are talking about.

To Fetch a Day's Appointments: Given a Timezone, determine the list of static DateRanges, 8am-8pm with breaks. Next fetch all the Appointments by DateRange that fall within this.

Concurrency

The active schedule is time sensitive and represent a limited quantity resource that users are competing for (you have to look at it in these terms). Locking the Appointment table during validation and scheduling for a single user is necessary to preven double booking.

Algorithm

Once you have fetched a Day for a given user and their respective Timezone:

Loop through the static Day DateRange's and make sure that the requested appointment time falls within one of these ranges.
Next loop through the already scheduled appointments and make sure that the requested appointment time does not overlap with any existing scheduled appointments.
If these validations pass then create a new Appointment with its appropriate DateRange and persist.
Lather rinse and repeat...

Algorithm for fast tag search

i would do this in sql having a link table EntityCategory between eid referencing entity and cid referencing category using self-joins:

    select count(ec1.eid)
    from EntityCategory ec1 
    left join EntityCategory ec2 on ec1.eid=ec2.eid 
    left join EntityCategory ec3 on ec1.eid=ec3.eid 
    ...
    where 
      ec1.cid={categoryId1} and 
      ec2.cid={categoryId2} and
      ec3.cid={categoryId3} ...

Best Answer

Related Solutions

Algorithms – How to Figure Out Appointment Times

Data Model

Concurrency

Algorithm

Algorithm for fast tag search

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