6.1 What is an identifier?6.2 What makes a good identifier?6.2.1 Easy to use6.2.2 Unique6.2.3 Permanent6.2.4 Fast and easy to generate6.2.5 Unpredictable6.2.6 Readable, shareable, and verifiable6.2.7 Informationally dense6.3 What does a good identifier look like?6.3.1 Data type6.3.2 Character set6.3.3 Identifier format6.3.4 Checksums6.3.5 Resource type6.3.6 Hierarchy and uniqueness scope6.4 Implementation6.4.1 Size6.4.2 Generation6.4.3 Tomb-stoning6.4.4 Checksum6.4.5 Database storage6.5 What about UUIDs?6.6 ExercisesSummary