Tutorial

Create a Perspective and add content

Adding a new perspective is as easy as

const myPerspective = await ad4m.perspective.add("My new perspective");

The returned object is of type PerspectiveProxy, which hides all the remote calls to the AD4M executor and can be treated like a local database object.

Perspectives are basically local graph databases. We can query all links on that proxy object with get:

const allLinks = await myPerspective.get(new LinkQuery({})); // => []

In this case it should return an empty array since we just created that perspective.

So let's add something! With the following code I'm creating an adhoc semantic statement representing what I think about AD4M...

import { Literal } from "@coasys/ad4m";
 
const me = await ad4m.agent.me();
const source = me.did;
const predicate = Literal.from("thinks").toUrl();
const target = Literal.from("AD4M will be the last social network").toUrl();
 
const linkExpresion = await myPerspective.add({ source, predicate, target });

Links consist of 3 URIs pointing to Expressions of Languages. For this example, we made life easy by using the agent's DID and AD4M's Literal Language.

Agent DID

For the source of our link, we got the user's DID URI by first getting the users Agent object with ad4m.agent.me(). That has a DID property and DID URIs are considered valid URIs in AD4M (they can be looked-up using the Agent bootstrap language which resolves to the same Agent object we got through ad4m.agent.me() - just even if that agent behind the resolved DID isn't me).

Literal

The Literal Language is an AD4M Language without back-end. It stores JavaScript literals (i.e. strings, numbers and objects) by encoding them into the Expression URL. So,

Literal.from("thinks").toUrl();

returns literal://string:thinks - which is a valid URI - and

Literal.from("AD4M will be the last social network").toUrl();

returns literal://string:AD4M%20will%20be%20the%20last%20social%20network. This is basically like URL parameters and let's us get around introducing Languages before using Perspectives and Links.

We can decode the URL into a JavaScript literal like so:

const string = Literal.fromUrl("literal://string:thinks").get();
// string == 'thinks'

LinkExpression

We have put in a Link object into myPerspective.add() ({source, predicate, target}), but what this function returns is a LinkExpression.

Even though this Perspective is not shared (yet) but just our private, local graph database, we might want to share it later as Neighbourhood. Then, all links added by some agent to their local Perspective will be shared with the other agents using a LinkLanguage - a Language which defines Expressions representing Links. That is LinkExpressions.

Using the generic Expression template, LinkExpressions wrap Links with author, timestamp and signature:

{
    author: "did:key:zQ3shNWd4bg67ktTVg9EMnnrsRjhkH6cRNCjRRxfTaTqBniAf",
    timestamp: "Sun Oct 23 2022 15:31:52 GMT+0200 (Central European Summer Time)",
    data: {
        source: "did:key:zQ3shNWd4bg67ktTVg9EMnnrsRjhkH6cRNCjRRxfTaTqBniAf",
        predicate: "literal://string:thinks",
        target: "literal://string:AD4M%20will%20be%20the%20last%20social%20network",
    },
    proof: {
        key: "#zQ3shNWd4bg67ktTVg9EMnnrsRjhkH6cRNCjRRxfTaTqBniAf",
        signature: "xxxx",
    }
}