RDF-XML Code Snippet 1
1 2014-10-01T16:38:32-07:00 Erik Loyer f862727c4b34febd6a0341bffd27f168a35aa637 3296 2 Sample RDF-XML Code For Scalar's API plain 2015-05-28T15:29:45-07:00 Erik Loyer f862727c4b34febd6a0341bffd27f168a35aa637This page is referenced by:
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Reading Content from the API
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Understanding the RDF syntax used in Scalar's API
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All API results are returned in RDF, serialized as either RDF-XML or RDF-JSON. The serialization can be managed by the ?format=[xml|json] GET variable (xml is the default). RDF can be intimidating when first encountered. However, it can be summed up by stating that it is content presented in a flatted or non-hierarchical way. For example, each Scalar node — page, media, annotation, etc. — is a node in the RDF output. Additionally, each relationship is also a node, linking two other nodes together. The relationship nodes are at the same hierarchical level as the content nodes, thus presenting RDF’s flattened hierarchy.
Content Nodes
As a practical example, consider the home page of this User's Guide represented in RDF-XML:
In the above example, you can see that a piece of Scalar content is broken into two RDF nodes: first, the content wrapper, and then its version. In this case, the version number 23 of the piece of content is output.
Relationship Nodes
Now consider a second piece of content with the URL, http://scalar.usc.edu/works/guide/getting-started. To create a relationship between the two pieces of content, a third node can be provided in RDF when the recursion level of the RDF is greater than zero (e.g., using the ?rec=1 GET variable) stating that the output is recursing relationships to the first degree. In the example below, you can find the first relationship node by looking for "<rdf:Description rdf:about="urn:scalar:path:210521:36977">":
In this relationship node, a body (oac:hasBody) is described as the home page (/index), and the target (oac:hasTarget) as the getting started page (/getting-started). The hash fragment (the string after the # character) of the target describes the type of relationship, in this case “getting started” is index 1 of the home page. Put another way, the home page is a path containing other pages where “getting started” is the first page in the path. If no hash fragment is present on the target then the relationship is a Tag. Other relationships types will have different hash fragments.
RDF-JSON
RDF-XML can be difficult to parse (for example, in JavaScript and PHP), therefore the Scalar API also offers the same data in the RDF-JSON format. Here is similar content to that described above outputted in JSON format (using the ?format=json GET variable):
In RDF-JSON, data is provided as an object. The only difference between an RDF-JSON object and a typical JSON object is that rather than index numbers to denote each node as in JSON (e.g., 0, 1, 2, …), in RDF-JSON the URL of each node acts as its key.
Sample Code
Pages and Versions can be easily placed into lists by looking at each node’s “rdf:type” which will be one of Composite, Media, or Version.
var pages = [], versions = []; for (uri in json) { var type = json[uri][‘http://www.w3.org/1999/02/22-rdf-syntax-ns#type’]; if (-1!=type.indexOf(‘Composite’)||-1!=type.indexOf(‘Media)) pages.push(json[uri]); if (-1 != type.indexOf(‘Version’)) versions.push(json[uri]); }