The notebook index
Earlier notes
Earlier reference notes remain available at their existing addresses. The current blog concentrates on programming languages, protocols and self-hosted software.
310 notes.
- What Makes a GTFS Feed a Complete Dataset?
Feed completeness depends on the specification’s file and field requirements, including requirements that apply only under stated conditions.
- How Should a GTFS Publisher Version a Schedule Feed?
A schedule release should be identifiable as a coherent dataset and retrievable from a public location whose purpose does not change between releases.
- How Do Calendar Exceptions Interact with Weekly Service?
GTFS weekly service patterns establish recurring dates, while calendar-date exceptions adjust the service that applies on a particular date.
- What Role Does stop_times.txt Play in GTFS?
stop_times.txt links a trip to its ordered stops and scheduled passage times, allowing a consumer to reconstruct its stop-level itinerary.
- How Can GTFS Transfers Describe a Connection?
Transfer records can express how locations relate for a change between trips, but a represented connection is not automatically a guaranteed connection.
- What Is the Purpose of GTFS shapes.txt?
Route shapes provide geometry that can help map a transit service, while stop times remain the source for the trip’s ordered scheduled stops.
- How Should a GTFS Consumer Treat Optional Fields?
A robust GTFS consumer follows each field’s stated presence condition and handles valid omission without inventing a replacement value.
- What Is a Protocol’s Compatibility Policy?
A compatibility policy tells implementers how revisions affect existing clients and how to recognize changes that require coordinated upgrades.
- How Does ActivityPub Deliver an Activity?
Activity delivery connects an actor’s action, its addressed recipients, a delivery endpoint, and receiver-side processing across separate servers.
- What Is the Role of an Actor Identifier in ActivityPub?
An actor identifier provides a stable reference that links an account’s published profile information to protocol actions involving that actor.
- How Should a Federated Server Handle a Repeated Activity?
A federated server should use stable activity identity to recognize redelivery and make processing safe to repeat without creating duplicate effects.
- What Does Web Linking Contribute to Protocol Design?
Typed links let protocols connect resources while making the target and the relationship between resources explicit.
- How Do Protocols Represent Optional Capabilities?
Capability discovery lets peers advertise supported extensions so each side can choose a defined fallback when a feature is unavailable.
- Why Should Protocol Errors Have Stable Codes?
Stable error codes let clients respond consistently while giving operators clear, human-readable explanations.
- How Can a Protocol Specify Retry Behavior?
A retry contract should say which failures are temporary, how clients should wait, and how to avoid repeating side effects.
- What Is the Difference Between Transport and Application Protocol?
Transport rules move data between endpoints; application rules give that data meaning and define what participants do with it.
- How Should a Protocol Handle Unknown Fields?
A protocol should make explicit whether unknown fields are ignored, retained, or rejected, because the safe rule depends on context.
- How Can a Protocol Document Authentication Requirements?
Authentication documentation should identify credentials, their transport protection, the permissions they carry, and clear failure behavior.
- What Should a Protocol Say About Timestamps?
A timestamp needs a defined representation, time zone, precision, and event meaning before different systems can interpret it consistently.
- How Do GTFS Fare Files Relate to a Trip?
GTFS fare data describes products and rules that may apply across a rider’s journey, so interpreting a trip can require more than reading one route record.
- What Is a Practical Exercise for Reading a Protocol Reference?
Tracing one field from its declared type through its presence rule and meaning is a compact exercise in reading specifications carefully.
- Why Should a Protocol Reference Define Normative Terms?
Defined normative terms distinguish mandatory requirements from recommendations and options, helping independent implementations make compatible choices.
- How Can Protocols Handle Partial Failure?
A partial-failure contract identifies what succeeded, what failed, and which recovery actions are safe when an operation has multiple effects.
- What Makes a Protocol Example Interoperable?
An interoperable example is complete, valid, and explicit about the encoding and context needed for another implementer to reproduce its meaning.
- How Should a Protocol Publish Revision History?
A useful revision history records when a version changed, what changed, and how the change affects compatibility and implementers.
- What Is a Safe Way to Extend a Data Protocol?
Safe extensions use clearly reserved space, preserve predictable behavior for older clients, and define how new meaning is discovered.
- How Can Readers Compare Two Protocol Specifications?
Comparing protocols works best when readers examine message structure, identity, delivery, failures, and evolution using the same questions.
- How Can You Test a GTFS Service Calendar Parser?
Build small calendar fixtures that exercise weekly rules, date exceptions, and feed-range boundaries.
- What Test Catches Transit Times Beyond Midnight?
Test service-day time arithmetic with a value such as 25:15 and verify its next-day calendar result.
- How Should You Test Daylight-Saving Boundaries?
Test local clock transitions with explicit zones and distinguish elapsed duration from wall-clock labels.