Project Decorum will use two endorsement (like/upvote) systems to thwart sybil attacks that could be launched against a decentralised endorsement system. In centralised systems like Facebook or reddit, there is a central authority that actively fights against bots registering many accounts to endorse content en masse. In SAFE we won't have that, people can create many identities if they wish (which has many benefits as well). So there will be two base types of endorsements in Decorum:

• Endorsements in the form of cryptographic signatures. These are only relevant within the context of a web of trust.
• Endorsements in the form of irreversibly attaching Clike, Project Decorum's coin-like token. These endorsements are generally relevant, it doesn't matter who attached them because a price is paid.

Web of Trust
Project Decorum's Web of Trust is a 'weaker' web of trust than the Web of Trust in PGP and such, which are concerned with establishing that digital identity X truly belongs to real-life person Y. With Project Decorum, we are concerned with establishing that digital identity X is a "legitimate" identity of someone rather than being "spam identity number 295317".

Management of this web of trust is mostly automated based on how you (and others already in your web of trust) treat the identity in question. If the identity receives several endorsements (from you or others that you already "trust") it's "trust" score increases, if the identity is blacklisted by others you trust, your trust score of it decreases. A high trust score will make that identity's actions (like endorsements) count, while the actions of an identity with no or a low trust score will have no meaning to you (their endorsements are not counted).

This means that the endorsements (of the signature variety) from an identity that hasn't integrated itself into the web of trust of a particular community have no meaning to that community. The inverse is also true, such an identity doesn't know whose endorsements from that community should be "trusted". Such segregation can be undesirable, hence:

Clike endorsements
The Clike attachment endorsement type bridges this gap. The philosophy behind this endorsement type is that when someone is willing to spend something of value to endorse something, then that something will likely also be more valueable to others compared to something that no one is willing to spend any value on to endorse.

In Project Decorum all content is organised and displayed in collections of some sort. For example, a forum category is a collection of topics, and a topic is a collection of replies. Clike endorsements are tracked per collection, and the endorsements for different content within a collection compete with each other. This is because these endorsements are registered in chronological order, and new endorsements decrease the weight of the older endorsements. This will ensure a degree of freshness of highest rated content and competition between promoters.

Note that the source of these endorsements is not considered, so unlike trusted endorsements, one party can give one piece of content as many as it wants and can afford. Also, while the Clikes cannot be recovered, the endorsement they represent can be invalidated if the endorser changes his/her mind.

Combining endorsement scores
So we have two different types of endorsements, and while these will be displayed separately, in many situations it is desirable to combine them into a final score, for example to generate a "most popular" list.

Content that scores high in both types of endorsements will receive an extra boost, while content that is blacklisted by members from your web of trust will receive a severe penalty and may not be displayed at all, despite having a lot of Clike endorsements. This will cause paid promotion of generally undesirable/inappropriate content to be relatively ineffective.