Phlex/FORM integration

[knoepfel]

This discussion serves as the central hub for discussing Phlex/FORM integration issues in preparation for Phlex v0.3.0.

[knoepfel]

@pcanal, @gemmeren, @wwuoneway, @aolivier23, and @knoepfel met on April 9, 2026 to discuss next steps in preparation for Phlex v0.3.0 (and beyond). My summary of the meeting is below.

A. For Phlex v0.3.0

1. Phlex v0.3.0 will support reading one FORM file as input (we will tackle reading multiple input files in FY27).
2. Phlex will enable the registration of providers that return type-erased data.
3. A goal is to retain the semantic distinction between framework drivers and data-product providers, while efficiently communicating data-cell indices (and other relevant metadata) between drivers and providers.
4. Right now, it is sufficient to use a data-cell index iterator which supplies one data-cell index at a time.
   • We do not need to support processing a range of data cells at one time.
5. The data-layer hierarchy will not be known until the file is opened (in contrast to the phlex::fixed_hierarchy behavior supported by Phlex v0.2.0):
   • Phlex will implement a driver interface that enables the opening of an input file
   • Upon opening that file, FORM will provide metadata that will be used by the framework to synthesize a provider node for each data product required from the input file.

B. After Phlex v0.3.0

1. The framework will need to be able to update the processed data-layer hierarchy when opening another input file.
2. The framework may support a running mode where all input files are declared to adhere to a specific hierarchy, thus avoiding unnecessary checking of the hierarchy contained in each file.
3. More than one input file may need to be open at the same time to support multi-threaded execution.

[pcanal]

I am confused in the ordering of 'v0.3.0 bullet 5' and 'after v0.3.0 bullet 2' as the later seem simpler to implement (Isn't the data-layer hierarchy determined by the graph described by the user configuration and the file either provide or do not provide the required input?)

[knoepfel]

Bullet B2 (sections now labeled) is meant to refer to a situation where a data-management system declares to Phlex what the hierarchy is for the files in that dataset. I can adjust the wording.