Add minimal example datasets for PQG education

[rdhyee]

Summary

• Add small, hand-crafted example datasets to help understand the iSamples PQG format
• Same data represented in JSON, CSV, and all three parquet formats (export, narrow, wide)

Dataset Overview

Domain: Geological rock samples from Mount Rainier volcanic monitoring project

Entities:

• 3 MaterialSampleRecords (samples)
• 3 SamplingEvents (collection/preparation events)
• 2 GeospatialCoordLocations (coordinates)
• 1 SamplingSite (Mount Rainier Summit Area)
• 1 Agent (Jane Smith, collector)

Relationships demonstrated:

• Sample → produced_by → SamplingEvent (how samples are created)
• Sample → derivedFrom → Sample (parent/child relationship)
• SamplingEvent → sample_location → GeospatialCoordLocation
• SamplingEvent → sampling_site → SamplingSite
• SamplingSite → site_location → GeospatialCoordLocation

Files Added

pqg/examples/minimal/
├── README.md                      # Explains files, queries, format comparison
├── json/
│   ├── 1_sample.json              # Single MaterialSampleRecord
│   └── 3_samples.json             # Three related samples
├── csv/
│   ├── samples.csv                # MaterialSampleRecords
│   ├── events.csv                 # SamplingEvents
│   ├── locations.csv              # GeospatialCoordLocations
│   ├── sites.csv                  # SamplingSites
│   ├── agents.csv                 # Agents
│   └── edges.csv                  # Relationships (narrow format)
└── parquet/
    ├── minimal_export.parquet     # Export format (3 rows, nested)
    ├── minimal_narrow.parquet     # Narrow format (21 rows, with edges)
    └── minimal_wide.parquet       # Wide format (10 rows, p__* columns)

Test plan

• JSON files validate against iSamplesSchemaCore1.0.json
• Parquet files readable with DuckDB
• Example queries in README execute correctly
• Entity counts match across formats

🤖 Generated with Claude Code