Reference
System design glossary
Short definitions for terms used across the course.
- Functional requirement
- A capability the system must provide or a task a user must be able to complete.
- Quality requirement (often called a nonfunctional requirement)
- A measurable expectation for how well the system provides its capabilities, such as latency, availability, privacy, or accessibility.
- Constraint
- A boundary the solution must respect, such as a deadline, budget, geography, existing integration, or regulation.
- Assumption
- A statement treated as true for the current design because it is not yet confirmed. Record it so it can be checked and revised.
- Workload
- The user and system activity a design must handle, including request volume, data size, timing, and growth.
- Request rate
- The number of requests handled in a time interval. Requests per second (RPS) or queries per second (QPS) are common units.
- Throughput
- The amount of work completed per unit of time. It may be measured in requests, transactions, messages, or bytes.
- Peak factor
- A stated multiplier from average demand to a chosen peak estimate. It is a scenario assumption, not a universal constant.
- Read/write ratio
- The relative count of read requests to write requests over a defined interval. State the interval and what each request count includes.
- Bandwidth
- The data transferred per unit of time, commonly reported in bytes or bits per second. Identify the direction and payload being counted.
- Retention period
- How long data must remain available before deletion or archival, subject to product, legal, and operational requirements.
- Back-of-the-envelope estimate
- A quick, transparent approximation used to compare magnitudes and expose assumptions before detailed measurement.