I mentioned in an earlier post about Ning today that I felt that the content model used by functionally no different from RDF. This needs a bit of explanation, I’m sure, and thus far there isn’t a lot of talk out there about how to actually use the content store. (This is probably related to the significant lack of beta developer accounts so far, something that will hopefully change in the near future.)
A quick tutorial on creating Content Objects on Ning first (drawn from XN_Content documentation):
$object = XN_Content::create(”TypeOfObject”, “Title of Object”, “Description of Object”);
This creates an object with a Type, Title, Description. These are the three most commonly used “System” attributes — they are present on almost every object created in some form or another, so they can be used in displaying that data.
In addition to these system attributes, there is the ability to add developer attributes:
$object->my->name = “Christopher Schmidt”;
$object->my->age = 21;
If we look at the content for this object, via the $object->debugHTML() method, we see:
title [Title of Object]
description [Description Of Object]
ownerName [Example App]
my attributes [
[-1] name : Christopher Schmidt : string
[-1] age : 21 : number
Here we see some interesting bits that we hadn’t before: the id, Date, and owner fields are all useful for where the data is coming from, and the contributorName for who the data is coming from. For the time being, however, we’ll concentrate on the my attributes and the id and type system attributes.
Mapping this to an RDF representation is relatively simple:
ning:198390 a TypeOfObject;
dc:title “Title of Object”;
dc:description “Description of Object”;
ning:name “Christopher Schmidt”;
ning:age “21″ .
You’ll see here the main issue with representing Ning content objects as RDF: the fact that types and predicates (developer attributes) are stored only as strings, not the URIs that RDF typically asks for. This results in a less descriptive format than you would typically find in most RDF descriptions: there’s no URIs for predicates, so you can’t do some of the “magic” that RDF is famous for.
However, I have been working with RDF for more than 1.5 years now, and I have never had any use for that magic.
The ability to uniquely identify predicates may be useful in a general sense, and it provides the ability to accurately and adequately describe these predicates for use in other systems… but at the base level, they are designed to be able to attribute semantics to the terms. In many cases, these semantics are simply unneccesary: if I have a Book with an “isbn” property, I probably know what it’s going to be.
If you do need this level of semantics, all hope is not lost! You can still achieve your goals! Typically, apps use an attribute in only one way, and with each content object is the application which owns it. (In this case, exapp — which doesn’t exist, for the record. The minimum length is 6 characters.) So, you can take the URL for the app (http://exapp.ning.com/) and create a URL based on that: whether it’s in the app’s namespace (squatting on a URL that it isn’t using, for example) or in your own. I could coin http://crschmidt.net/ns/ning-exapp# for a prefix to predicate URLs in this situation.
The semantics attached to a predicate are extremely weak in the Ning content store — but that doesn’t mean that they are useless. It is my opinion that a simple RDF representation of Ning content objects can be useful in many cases, and that the model that is in use succeeds in proving that the RDF model as an application data store is not useless, but instead can lead to rich applications sharing data, as Ning is specifically designed to accomplish.
One thing I didn’t mention above is that it is possible to create links, not only to literals and numbers, but also to other content objects:
$object->my->otherContent = XN_Content::create(”OtherObject”);
This creates a link to another content object, by that object’s ID. This fits perfectly into the RDF model, where URLs identify an object: the Content Object’s ID is its unique identifier within the Ning universe, and the backing store lets you link any number of these objects together. You want to grab a book that someone added, and tie it to your own? That’s fine! Simply create a Content Object and add both of those as attributes. You want a whole list of books from someone else’s bookshelf? That’s fine too: just grab the IDs, and attach em. This casual interlinking of data is exactly what is going to make Ning a success — and it’s exactly the kind of interrelationship that proves the RDF model is not wrong.
I know that some people will strongly disagree: they will say that the Ning content model is more demonstration that people “don’t get it”. What I see it as is exactly the opposite: it’s proof that regardless of the underlying way content is stored, it can be presented to applications in a way that is easy to use, and useful. By giving objects a Unique Identifier (whether it’s a URI or an ID), a way to connect them together, and a decent API to put it all in place in code, you can create magic.