Provider Schedule Model
A provider’s schedule is defined at two levels: recurring availability rules and date-specific overrides. Recurring rules describe the baseline: "Dr. Smith is available Monday through Friday, 9am to 5pm, with a 30-minute lunch break from 12:00 to 12:30." Overrides handle exceptions: holidays, vacation days, conference days, or one-off extended hours. The schedule is stored as rules, not as pre-expanded slots — expanding every possible appointment slot for the next year would be millions of rows per provider.
Each availability block carries metadata about which appointment types it supports. A new-patient slot requires 60 minutes; a follow-up visit 30 minutes; a procedure 90 minutes. Some blocks restrict appointment types: a provider may only accept new-patient appointments on certain days. Appointment type constraints are stored on the availability block and enforced during slot generation and booking.
The schedule model also tracks provider-specific booking rules: minimum advance notice (e.g., no same-day new-patient bookings), maximum advance booking window (e.g., no bookings more than 90 days out), and buffer time between appointments. These rules are applied during slot generation to ensure the expanded slot grid is consistent with the provider’s actual availability.
Slot Generation
Slot generation expands availability rules into discrete, bookable time slots for a look-ahead window (typically 4–12 weeks). The expansion algorithm walks each day in the window, applies the provider’s recurring rules, applies any date overrides, and subdivides available blocks into slots based on appointment type duration. Buffers between appointments are removed from the available time before subdivision.
Generated slots are stored in the appointment_slots table: slot_id, provider_id, start_time, end_time, appointment_type, status (available|booked|blocked), patient_id, created_at, updated_at. Slots are indexed by (provider_id, start_time, status) for efficient availability queries. A daily batch job generates slots for the newly-added dates at the edge of the look-ahead window.
Blocked slots handle non-appointment time: staff meetings, administrative blocks, lunch. These are written directly as status=blocked slots by the scheduling system or by clinic staff through an admin interface. A provider can also manually block individual slots (e.g., to keep time open for a specific patient or urgent add-on). Blocked slots are never returned in patient-facing availability queries.
Booking Conflict Prevention
The core concurrency challenge: two patients attempting to book the same slot at the same time. The naive SELECT-then-UPDATE approach has a race condition — both patients see the slot as available, both try to book, and one ends up with a booking on an already-booked slot. Two approaches handle this correctly.
Optimistic locking: UPDATE appointment_slots SET status='booked', patient_id=X WHERE slot_id=Y AND status='available'. Check the number of rows updated. If zero rows were updated, someone else booked the slot first — return an error to the client with a list of next-available slots. The client retries with a different slot. This approach has minimal database overhead for the common case (no contention) and degrades gracefully under contention.
Pessimistic locking: SELECT slot_id FROM appointment_slots WHERE slot_id=Y FOR UPDATE, followed by the UPDATE. This serializes concurrent bookings for the same slot at the database level. Prefer optimistic locking for typical scheduling load (low contention per slot); use pessimistic locking if high-volume flash booking events (e.g., a popular specialist opening new slots) cause excessive optimistic retry rates. In either case, the booking endpoint is idempotent via an idempotency key on the booking request.
HIPAA Compliance
Protected Health Information (PHI) includes patient names, dates of birth, contact information, appointment types, diagnoses, and any clinical notes. HIPAA requires PHI to be encrypted at rest (AES-256) and in transit (TLS 1.2+). Database columns containing PHI are encrypted at the application layer before storage, or the database volume is encrypted with key management via AWS KMS or equivalent. Encryption keys are rotated annually.
Access controls enforce the minimum necessary standard: providers see only their own patients’ records; patients see only their own records; clinic staff see records for patients in their clinic; no cross-clinic access without explicit authorization. Role-based access control (RBAC) is enforced at the API layer, not just the UI layer. Direct database access for any purpose requires approval and is logged.
Every access to a patient record — read or write — is written to an immutable audit log: audit_id, user_id, patient_id, record_type, action, timestamp, ip_address, session_id. Audit logs are stored separately from application data and cannot be deleted by application users. HIPAA requires the ability to produce audit logs for any patient record on request, covering the prior 6 years. Business Associate Agreements (BAA) are required with all cloud infrastructure vendors before any PHI is stored on their systems.
Reminder System
Automated reminders reduce no-show rates, which are costly for providers and delay care for other patients. The reminder schedule per appointment: 72 hours before (allows cancellation with enough notice for the slot to be rebooked), 24 hours before (final confirmation request), 2 hours before (day-of reminder). Patients can configure their preferred channel per reminder type: email, SMS, push notification, or voice call.
Reminders are stored as scheduled jobs in the reminder_jobs table at booking time: job_id, appointment_id, patient_id, send_at, channel, status, sent_at. A worker process polls for jobs due in the next 5 minutes and dispatches them through the appropriate delivery channel (SendGrid for email, Twilio for SMS and voice, FCM/APNs for push). Delivery status is tracked via webhooks from the channel providers.
No-show detection runs 15 minutes after appointment start time. If the patient has not checked in (via EHR, kiosk, or app), the appointment is flagged as a potential no-show and the provider is notified. Confirmed no-shows are recorded on the patient’s account. Patients with high no-show rates (above 3 in 12 months) are flagged in the booking system; the clinic can configure whether to restrict advance booking, require prepayment, or apply a no-show fee.
Telehealth Integration
Telehealth appointments require a HIPAA-compliant video platform. Options: Zoom for Healthcare (BAA available), Daily.co, Doxy.me, or a custom WebRTC implementation. On booking a telehealth appointment, the system calls the video platform API to create a meeting room and generates unique join links for the patient and provider. Join links are sent in the confirmation email and are accessible from the patient app and provider EHR interface.
The meeting room is activated 10 minutes before the appointment start time. If the patient or provider joins before the other, they see a waiting room screen. Session start and end times are recorded for billing (telehealth reimbursement often requires minimum session duration). Session recording is enabled only with explicit patient consent, captured and stored on the consent record before the session starts.
Connection quality is monitored via the video platform’s quality metrics API. Persistent poor quality (packet loss above threshold, resolution degraded) triggers an in-session alert suggesting the patient switch to a phone call. If video fails completely, the appointment falls back to a phone call and is still billable as a telehealth encounter in most payer contracts. Technical failure is recorded on the appointment record for billing dispute purposes.
Waitlist Management
When a patient cannot find a suitable available slot, they are added to a waitlist for that provider or appointment type. The waitlist record stores: patient_id, provider_id, appointment_type, earliest acceptable date, latest acceptable date, urgency score (set by provider or referring clinician), and the timestamp of waitlist entry. Waitlist position is ordered by urgency score descending, then by timestamp ascending (earlier entry wins ties).
On slot cancellation, the system immediately queries the waitlist for eligible patients (matching provider and appointment type, availability window overlaps with the freed slot). The top candidate receives a push notification and SMS: "A slot has opened with Dr. Smith on Tuesday at 2pm. Reply YES to book or this offer expires in 30 minutes." If no response within 30 minutes, the offer is made to the next candidate. Accepted offers create a booking via the same optimistic lock path as a direct booking.
Patients can be on multiple waitlists simultaneously. When one waitlist offer is accepted, the patient is automatically removed from all other waitlists for the same appointment type within the same date window. Providers and clinic staff can view the waitlist for their schedule and manually offer slots to specific waitlisted patients, bypassing the automated ordering — useful for urgent cases.
Multi-Provider Booking
A group practice allows patients to book with any provider in the practice. The booking interface shows a unified view: filter by specialty, language spoken, insurance accepted, and appointment type. Available slots across all matching providers are shown in a combined calendar view. The patient selects a specific provider and time, or opts for "first available" across all matching providers.
Concurrent booking requests for the same slot at the same provider are handled by the same optimistic lock mechanism as single-provider booking. When a slot is taken and the patient has selected "first available," the system automatically retries with the next available slot across the provider pool without requiring the patient to manually choose again. This retry loop runs server-side and completes in a single request from the patient’s perspective.
Provider assignment rules can be configured by the clinic: existing patients prefer their established provider; new patients are assigned by round-robin or by shortest wait time. Insurance verification — confirming the patient’s insurance covers the selected provider — runs as an async pre-check at booking time, with results returned before the patient confirms. Out-of-network warnings are surfaced in the booking flow, with estimated patient cost, before the appointment is finalized.
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