Atomic Schema FAQ

How do I create a Property that supports multiple Datatypes?

A property only has one single Datatype. However, feel free to create a new kind of Datatype that, in turn, refers to other Datatypes. Perhaps Generics, or Option like types should be part of the Atomic Base Datatypes.

Do you have an enum datatype?

In Atomic Data, enum is not a datatype, but it's a constraint that can be added to properties that have. You can set allows-only on a Property, and use that to limit which values are allowed.

How should a client deal with Shortname collisions?

Atomic Data guarantees Subject-Property uniqueness, which means that Valid Resources are guaranteed to have only one of each Property. Properties offer Shortnames, which are short strings. These strings should be unique inside Classes, but these are not guaranteed to be unique inside all Resources. Note that Resources can have multiple Classes, and through that, they can have colliding Shortnames. Resources are also free to include Properties from other Classes, and their Shortnames, too, might collide.

For example:

{
  "@id": "https://example.com/people/123",
  "https://example.com/name": "John",
  "https://another.example.com/someOtherName": "Martin"
}

Let's assume that https://example.com/name and https://another.example.com/someOtherName are Properties that have the Shortname: name.

What if a client tries something such as people123.name? To consistently return a single value, we need some type of precedence:

  1. The earlier Class mentioned in the isA Property of the resource. Resources can have multiple classes, but they appear in an ordered ResourceArray. Classes, internally should have no key collisions in required and recommended properties, which means that they might have. If these exist internally, sort the properties by how they are ordered in the isA array - first item is preferred.
  2. When the Properties are not part of any of the mentioned Classes, use Alphabetical sorting of the Property URL.

When shortname collisions are possible, it's recommended to not use the shortname, but use the URL of the Property:

people123."https://example.com/name"

It is likely that using the URL for keys is also the most performant, since it probably more closely mimics the internal data model.

Many features in Atomic Data apps depend on the availability of Resources on their subject URL. If that server is offline, or the URL has changed, the existing links will break. This is a fundamental problem to HTTP, and not unique to Atomic Data. Like with websites, hosts should make sure that their server stays available, and that URLs remain static.

One possible solution to this problem, is using Content Addressing, such as the IPFS protocol enables, which is why we're planning for using that in the near future.

Another approach, is using foreign keys (see issue).

How does Atomic Schema relate to RDF / SHACL / SheX / OWL / RDFS?

Atomic Schema is the schema language for Atomic Data, whereas RDF has a couple of competing ones, which all vary greatly. In short, OWL is not designed for schema validation, but SHACL and SheX can maybe be compared to Atomic Schema. An important difference is that SHACL and SheX have to deal with all the complexities of RDF, whereas Atomic Data is more constrained.

For more information, see RDF interoperability.

What are the risks of using Schema data hosted somewhere else?

Every time you use an external URL in your data, you kind of create a dependency. This is fundamental to linked data. In Atomic Data, not having access to the Property in some JSON-AD resource will lead to now knowing how to interpret the data itself. You will no longer know what the Datatype was (other than the native JSON datatype, of course), or what the semantic meaning was of the relationship.

There are multiple ways we can deal with this:

  • Cache dependencies: Atomic Server already stores a copy of every class and property that it uses by default. The /path endpoint then allows clients to fetch these from servers that have cached it. If the source goes offline, the validations can still be performed by the server. However, it might be a good idea to migrate the data to a hosted ontology, e.g. by cloning the cached ontology.
  • Content-addressing: using non-HTTP identifiers, such as with IPFS.

See discussion.