Solid Resources needs a way to tell what their containers are

Web Access Control Spec の Effective ACL Resource の計算に関するセクションと、URI のスラッシュのセマンティクスに関する Solid Protocol Spec セクション 3.1 を読み、その後、提案されている reverse-link アプローチと resource-type アプローチを比較します。クライアントが Solid containers をどのように区別するかについて決定し、その決定を関連する仕様に記録できれば完了です。

The Web Access Control Spec has a section on how to calculate the Effective ACL Resource by following a resource up to its "container resource".
The Solid Protocol Spec specifies using 3.1 URI Slash Semantics. So it is clear what the intention is.

But how is a client to know it has landed on a Solid server that implements those intentions rather than one that has not? There will be many LDP servers implemented by the LDP consortium members. A client can't distinguish between those servers and those implementing Solid, potentially leading to many unnecessary requests.

There are a number of ways of doing this.

1. Compatible with LDP servers: every resource has a reverse link to the container, which in Solid would always be ../, but on other LDP containers could be something else.

Link: <../>; rev="http://www.w3.org/ns/ldp#contains"

2. Specify that a resource is not an ldp:BasicContainer or ldp:Resource but a subset of those, namely a solid:Container or solid:Resource. Note this was proposed in the 2013 to the LDP group and later became issue-50.

Clearly, if a resource specifies that it is a solid resource, then point 1 is unnecessary as the URL structure contains the information about the ldp:contains link. On the other hand, for more lax servers following LDP, then 1 is needed.

I don't think that having an "acl" link header is enough to distinguish the server as being a solid one, as that link could very well also be used by LDP servers.