What defines a "platform"?

[AramZS]

The Signals Protocol specifies a "platform" and gives some different examples. This does not make it clear.

What is a "platform" in the AdCP context? Is it any system which can provide supply? Is it specific classifications of supply? Could it be a single publisher? A coalition of publishers? A single category of content on a single publisher? A middleman system that has no actual supply but will participate in order to gain parameters to arbitrage for supply? Is it anything that can mediate demand? What must a participant who is a "platform" bring to the table other then the responses to these particular API requests?

The specification needs clearer definition about what stakeholders are considered platforms here.

[AdButlerRob]

Curious on this one as well, as an ad-server, we're looking at the best way to fit into this picture as well, it's one thing to add support for signals that can be passed through, let's just say an OpenRTB request, that could then be transcribed into actions that AdCP could understand for a media buyer, though is there a step further here? Could a brand or advertiser have their own buying agent, that goes out and then communications directly with publisher ad servers directly? What an exciting time in an uncharted area and we're just scratching the surface. We're sold on the idea of AdCP though!

[bokelley]

This has been addressed through the glossary and consistent terminology updates.

Decisioning Platform is now clearly defined in the glossary:

Technical infrastructure that selects which ad to serve at impression time. Receives activated signals and executes campaigns. Examples: DSPs (The Trade Desk), SSPs (Index Exchange, OpenX, PubMatic), ad servers (Google Ad Manager, Kevel).

The key distinction in AdCP:

• Decisioning Platforms make ad selection decisions at impression time (DSPs, SSPs, ad servers like AdButler)
• Sales Agents expose publisher inventory for discovery and purchase

So to answer the original questions:

• A single publisher would be represented by a Sales Agent, not a platform
• A coalition of publishers could operate a Sales Agent
• "Middlemen" that make ad decisions are decisioning platforms; those exposing inventory are sales agents
• Ad servers (like AdButler per Rob's comment) are decisioning platforms

The type: "platform" discriminator in the Signals Protocol schemas refers specifically to decisioning platforms, as documented in the task references.