Record two source histories, then compare what they saw.

The shortest useful path: define one state window, ingest events from two sources, compare the recorded windows, and inspect the output.

Mental model

Start with one question: when was this state active?

A window opens when your predicate becomes true for a key and source. It closes when the predicate becomes false. Once those windows are recorded, compare sources without hand-written interval joins.

1. Install

Add the package to your project.

dotnet add package Spanfold

cd packages/python
python -m pip install -e ".[dev]"

The Python package includes the core runtime, comparison, export, testing, and CLI surfaces.

2. Minimal implementation

A complete first example.

This example uses processing positions rather than timestamps so the output is easy to inspect. Position 1 is the first ingested event, position 2 is the second, and so on.

using Spanfold;

var pipeline = Spanfold.Spanfold
    .For<DeviceStatus>()
    .RecordWindows()
    .TrackWindow(
        "DeviceOffline",
        key: status => status.DeviceId,
        isActive: status => !status.IsOnline);

Ingest("provider-a", isOnline: true);  // position 1
Ingest("provider-b", isOnline: true);  // position 2
Ingest("provider-a", isOnline: false); // position 3, provider-a opens
Ingest("provider-b", isOnline: false); // position 4, provider-b opens
Ingest("provider-b", isOnline: true);  // position 5, provider-b closes
Ingest("provider-a", isOnline: true);  // position 6, provider-a closes

var result = pipeline.History
    .Compare("Provider comparison")
    .Target("provider-a", selector => selector.Source("provider-a"))
    .Against("provider-b", selector => selector.Source("provider-b"))
    .Within(scope => scope.Window("DeviceOffline"))
    .Using(comparators => comparators.Overlap().Residual().Missing())
    .Run();

Console.WriteLine($"closed windows: {pipeline.History.ClosedWindows.Count}");
Console.WriteLine($"overlap rows: {result.OverlapRows.Count}");
Console.WriteLine($"provider-a-only rows: {result.ResidualRows.Count}");
Console.WriteLine($"provider-b-only rows: {result.MissingRows.Count}");

foreach (var row in result.OverlapRows)
{
    Console.WriteLine($"overlap {row.Key}: {row.Range.Start.Position}..{row.Range.End!.Value.Position}");
}

foreach (var row in result.ResidualRows)
{
    Console.WriteLine($"a-only {row.Key}: {row.Range.Start.Position}..{row.Range.End!.Value.Position}");
}

void Ingest(string source, bool isOnline)
{
    pipeline.Ingest(new DeviceStatus("device-17", isOnline), source);
}

public sealed record DeviceStatus(string DeviceId, bool IsOnline);

from dataclasses import dataclass

from spanfold import Spanfold


@dataclass(frozen=True)
class DeviceStatus:
    device_id: str
    is_online: bool


pipeline = (
    Spanfold.for_events()
    .record_windows()
    .track_window(
        "DeviceOffline",
        key=lambda status: status.device_id,
        is_active=lambda status: not status.is_online,
    )
)

pipeline.ingest(DeviceStatus("device-17", True), source="provider-a")
pipeline.ingest(DeviceStatus("device-17", True), source="provider-b")
pipeline.ingest(DeviceStatus("device-17", False), source="provider-a")
pipeline.ingest(DeviceStatus("device-17", False), source="provider-b")
pipeline.ingest(DeviceStatus("device-17", True), source="provider-b")
pipeline.ingest(DeviceStatus("device-17", True), source="provider-a")

result = (
    pipeline.history.compare("Provider comparison")
    .target("provider-a")
    .against("provider-b")
    .within(window_name="DeviceOffline")
    .using("overlap", "residual", "missing")
    .run()
)

print(f"closed windows: {len(pipeline.history.closed_windows)}")
print(f"overlap rows: {len(result.overlap_rows)}")
print(f"provider-a-only rows: {len(result.residual_rows)}")
print(f"provider-b-only rows: {len(result.missing_rows)}")

3. Expected output

The result should show one shared segment and two target-only segments.

closed windows: 2
overlap rows: 1
provider-a-only rows: 2
provider-b-only rows: 0
overlap device-17: 4..5
a-only device-17: 3..4
a-only device-17: 5..6

Provider A reported the device offline from position 3 to 6. Provider B reported it offline from position 4 to 5. Spanfold turns that into structured comparison rows: A-only before B saw it, overlap while both saw it, and A-only after B recovered.

4. What to try next

Move from the smallest case to useful diagnostics.

Open visual auditing examples See the same overlap and residual rows rendered as interactive timelines. Export agentic auditing context Generate agent-readable JSON with full result data and row-level evidence. Browse use cases Map temporal windows to monitoring, IoT, payments, logistics, and data pipelines. Use the API reference Look up builders, comparison rows, exports, liveness, and testing helpers. Run the samples Start with the single-lane device monitoring sample, then scale up to multi-source scenarios.