Data Flow

This page shows how data moves through the system, in the style of a data-flow diagram (DFD) suitable for the thesis.

Context diagram (Level 0)

Level 1 — main processes and stores

QR scan sequence

The most important runtime flow — a teacher scanning a student's code:

Each validation step can short-circuit with a specific message (invalid code, wrong teacher for the subject, not enrolled, already present). The full narrative is on the QR Attendance Flow page.

Notes on consistency

• Transactions. Attendance writes and their audit rows are committed together via prisma.$transaction(), so an attendance change never exists without its audit trail.
• Idempotent scans. A student already marked PRESENT for the day/subject is skipped, so repeated scans don't create duplicates or spurious audit rows.
• Date keys. The unique key (studentId, date, subjectId) uses a UTC-midnight date, guaranteeing one record per student per subject per day.