Manifesto

The HLL Forum maintains and develops the HLL language specification and promotes the use of HLL.

Its mission is to manage an open organization where users and tool providers collaborate to build a strong ecosystem around HLL and engage with other communities to broaden its adoption.

Its purpose is to ensure the long-term availability of HLL technology, interoperability among solutions from different

vendors, fair competition among vendors, and a sustainable HLL market.

Its actions aim to cultivate an active community that manages the language, defines its roadmap, and develops a pool of knowledgeable people, tools, and applications. This will strengthen the recognition of HLL as a standard language for formal verification.

History of the HLL language

Origin of HLL

2005

HLL was first developed in 2005 through an initiative by RATP (Parisian urban transport operator), which sought a powerful formal logic language for expressing safety properties and creating mathematical models for the formal verification of signaling systems. Over time, HLL became the de facto standard for formal verification in the rail and metro signaling domain, adopted by several major suppliers as well as infrastructure owners such as SNCF (French National Railways) and SL (Stockholm Public Transport).

HLL Specification 2.7 & Formation of the HLL Forum

2018

The HLL specification version 2.7 was published in 2018. With several tool suppliers, it became important to ensure that HLL evolved in a controlled manner, avoiding divergence between tool providers for the benefit of end-users. To address this, the HLL Forum was established during an inaugural meeting in Paris on December 4, 2018.

Unification of the Language

2019–today

After the Forum’s establishment, tool providers have collaborated to merge their various HLL dialects into a single unified language, together with RATP. The resulting language is HLL 4.0. It is released under a CC BY-ND 4.0 license to ensure large diffusion and freedom of use.