# Flo: a Semantic Foundation for Progressive Stream Processing

arXiv: https://arxiv.org/abs/2411.08274 · HTML: https://mlsanity.com/paper/2411.08274/

## Key facts

- Cited by 1 papers in the map (data through 14 Oct 2026).
- First posted on arXiv 13 Nov 2024.

## Built on by (most cited first, 1 of 1)

- [Dato: A Task-Based Programming Model for Dataflow Accelerators](https://mlsanity.com/paper/2509.06794/) (2025)

## Abstract (arXiv)

Streaming systems are present throughout modern applications, processing continuous data in real-time. Existing streaming languages have a variety of semantic models and guarantees that are often incompatible. Yet all these languages are considered "streaming" -- what do they have in common? In this paper, we identify two general yet precise semantic properties: streaming progress and eager execution. Together, they ensure that streaming outputs are deterministic and kept fresh with respect to streaming inputs. We formally define these properties in the context of Flo, a parameterized streaming language that abstracts over dataflow operators and the underlying structure of streams. It leverages a lightweight type system to distinguish bounded streams, which allow operators to block on termination, from unbounded ones. Furthermore, Flo provides constructs for dataflow composition and nested graphs with cycles. To demonstrate the generality of our properties, we show how key ideas from representative streaming and incremental computation systems -- Flink, LVars, and DBSP -- have semantics that can be modeled in Flo and guarantees that map to our properties.