LDflex for Solid

Simple access to data in Solid pods
through LDflex expressions


This library is a _configuration_ of
the LDflex language
for the Solid ecosystem.
It configures LDflex with:

1. a JSON-LD context for Solid
2. a Solid-authenticated query engine (Comunica or rdflib.js)
3. useful data paths for Solid

LDflex expressions occur for example
on Solid React components,
where they make it easy for developers
to specify what data they want to show.
They can also be used as an expression language
in any other Solid project or framework.

Creating data paths

Once you obtain the solid.data object,
start writing data paths from the following entry points.

$3

The solid.data.user path can query data about the currently logged in user,
such as:
- solid.data.user.firstName yields the user's first name(s)
- solid.data.user.email yields the user's email address(es)
- solid.data.user.friends yields the user's friend(s)
- solid.data.user.friends.firstName yields the user's friends' first name(s)

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The solid.data[url] path can query data about any subject by URL,
such as:
- solid.data['https://ruben.verborgh.org/profile/#me'].firstName
- solid.data['https://ruben.verborgh.org/profile/#me'].email
- solid.data['https://ruben.verborgh.org/profile/#me'].friends
- solid.data['https://ruben.verborgh.org/profile/#me'].friends.firstName

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As you can see in the above examples,
an LDflex path starts with an entry point
and is followed by property names,
which can be:

- abbreviations
such as firstName
(which expands to http://xmlns.com/foaf/0.1/givenName)
- prefixed names
such as foaf:givenName
(which expands to http://xmlns.com/foaf/0.1/givenName)
- full URLs
such as http://xmlns.com/foaf/0.1/givenName

The abbreviations and prefixed names are expanded
using a JSON-LD context.
You can find some inspiration about what to ask for in this context.

You can access data using any vocabulary you want
and, when included in the JSON-LD context, in multiple ways.
For example:
- FOAF:
- solid.data.user.name
- solid.data.user.foaf_name
- solid.data.user.foaf$name
- solid.data.user['foaf:name']
- solid.data.user['http://xmlns.com/foaf/0.1/name']
- vCard:
- solid.data.user.vcard_fn
- solid.data.user.vcard$fn
- solid.data.user['vcard:fn']
- solid.data.user['http://www.w3.org/2006/vcard/ns#fn']
- Schema.org:
- solid.data.user.schema_name
- solid.data.user.schema$name
- solid.data.user['schema:name']
- solid.data.user['http://www.schema.org/name']
- Custom:
- solid.data.user['http://example.org/my-ontology/name']

The traditional colon syntax for prefixes (schema:name)
can be substituted with an underscore (schema_name)
or dollar sign (schema$name).
This is because JavaScript keys with a colon
require quotes (user['schema:name'])
whereas underscores and dollar signs
can be used freely (user.schema_name, user.schema$name).

Installation

``bash
npm install @solid/query-ldflex
`

Usage

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`javascript
const { default: data } = require('@solid/query-ldflex');

const ruben = data['https://ruben.verborgh.org/profile/#me'];
showProfile(ruben);

async function showProfile(person) {
const label = await person.label;
console.log(\nNAME: ${label});

console.log('\nTYPES');
for await (const type of person.type)
console.log( - ${type});

console.log('\nFRIENDS');
for await (const name of person.friends.firstName)
console.log( - ${name} is a friend);
}

`

If, instead of Comunica,
you want to use the rdflib.js query engine,
install @ldflex/rdflib as a dependency of your project
and use

`javascript
const { default: data } = require('@solid/query-ldflex/lib/exports/rdflib');
`

When creating browser builds,
it can be easier to simply tell webpack
to replace @ldflex/comunica by @ldflex/rdflib.




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`html


`

`javascript
document.addEventListener('DOMContentLoaded', async () => {
const user = solid.data.user;
alert(Welcome, ${await user.firstName}!);
});

`

To replace Comunica by rdflib.js,
opt for

`html



`

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In addition to the default properties,
you might want to support your own:

`javascript
console.log(solid.data.context); // the raw default JSON-LD context
await solid.data.context.extend({ // add new JSON-LD context
con: 'http://www.w3.org/2000/10/swap/pim/contact#',
preferred: 'con:preferredURI',
});
console.log(await solid.data.context); // the expanded JSON-LD context

// Now we can use both existing and new properties
const ruben = solid.data['https://ruben.verborgh.org/profile/#me'];
console.log(await ruben.name);
console.log(await ruben.preferred);
`

Be aware though that this leads to expressions that are less portable,
because they only work when the additional context is added.

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LDflex expressions are actual JavaScript—not strings.
There are times when strings are more useful though,
such as when building
declarative components that take LDflex expressions.

The solid.data object exports a resolve interface
that transforms a string expression into an actual LDflex path.
This string is appended to solid.data to obtain the resulting path.
For example:
- solid.data.resolve('.user.firstName') becomes the path solid.data.user.firstName
- solid.data.resolve('["https://example.org/"].label') becomes the path solid.data["https://example.org/"].label

For convenience, the starting dot
and quotes inside of brackets can be omitted.
If the path is a single URL,
quotes and brackets can be omitted.
The following strings will all resolve:
- '.user.firstName'
- 'user.firstName'
- '["https://example.org/"].label'
- '[https://example.org/].label'
- 'https://example.org/'`

License

©2018–present Ruben Verborgh,
MIT License.