Tempo Network

Chronological networks and dependency scheduling for Tempo: periods known only relative to one another, the relations between them, and what follows from what you know.

Features

• Chronological networks — Tempo.Network holds periods whose starts, ends and lengths may each be exact, one-sided, a range or unknown, with the sequences and relations that tie them. Tempo.Network.Solver says whether what you have stated can all be true, and gives the tightest dates each period can take.

• Dependency scheduling — Tempo.Schedule plans tasks with lengths and dependencies: when each can start at the earliest and at the latest, which have slack, and the critical path.

• Allen's relations alone — Tempo.Interval.RelationNetwork reasons with Allen's relations alone, where no date or length is known.

Before Tempo 2.0 these modules were part of ex_tempo. Their names are unchanged.

Supported Elixir and OTP versions

Tempo Network supports Elixir 1.17 and later on Erlang/OTP 27 and later.

Installation

def deps do
  [
    {:ex_tempo, "~> 2.0"},
    {:ex_tempo_network, "~> 1.0"}
  ]
end

Quick start

A plan

iex> import Tempo.Sigils
iex> {:ok, plan} =
...>   Tempo.Schedule.new()
...>   |> Tempo.Schedule.task(:design, duration: ~o"P2D", start: ~o"2026-06-01")
...>   |> Tempo.Schedule.task(:build, duration: ~o"P3D", after: :design)
...>   |> Tempo.Schedule.task(:docs, duration: ~o"P1D", after: :design)
...>   |> Tempo.Schedule.task(:ship, duration: ~o"P2D", after: [:build, :docs], deadline: ~o"2026-06-08")
...>   |> Tempo.Schedule.solve()
iex> plan[:ship].early
~o"2026Y6M6D/7D"
iex> plan[:docs].critical?
false
iex> Tempo.Schedule.critical_path(plan)
[:design, :build, :ship]

"Design for two days from the first of June, then build and document, then ship by the eighth. Shipping takes the sixth and the seventh; the documentation has slack; the critical path is design, build, ship."

A chronology

iex> import Tempo.Sigils
iex> alias Tempo.Network
iex> network =
...>   Network.new()
...>   |> Network.add_period(:k1, from: {:not_before, ~o"1200Y"}, duration: {:at_most, ~o"P10Y"})
...>   |> Network.add_period(:k2, to: {:not_after, ~o"1300Y"}, duration: {:at_least, ~o"P35Y"})
...>   |> Network.add_sequence([:k1, :k2])
iex> Network.Solver.consistent?(network)
true
iex> {:ok, solved} = Network.Solver.propagate(network)
iex> solved.periods[:k2].latest_start
~o"1265Y"

"King K1 began no earlier than 1200 and reigned at most ten years; K2 followed him, reigned at least thirty-five and was gone by 1300. So K2 came to the throne no later than 1265."

The Chronological networks guide takes a whole chronology through stating, checking, tightening and tracing.

Written ends

Tempo writes an interval as it is said: an end written to a date is the date the interval runs through. A two-day task that starts on 1 June is therefore ~o"2026-06-01/2026-06-02", where ex_tempo 1.x wrote 2026-06-01/2026-06-03. A network's own bounds (earliest_start, latest_end and the rest) are points and are unchanged.

Documentation

• Chronological networks — a whole chronology through stating, checking, tightening and tracing.

The full documentation, every module and function with the guide, is on HexDocs.

License

Tempo Network is licensed under the Apache License 2.0; see LICENSE.md.