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Context prefixes not loading in JsonLdParser.Load

I'm trying to load some basic json-ld content as a string, but I'm not able to see the namespace prefixes that should be included.
Given the following json-ld:
{
"#context": {
"name": "http://schema.org/name",
"image": {
"#id": "http://schema.org/image",
"#type": "#id"
},
"foaf": "http://xmlns.com/foaf/0.1/"
},
"name": "Manu Sporny",
"foaf:homepage": "http://manu.sporny.org/",
"image": "http://manu.sporny.org/images/manu.png"
}
I run this against the dotnetrdf library:
void Main()
{
var targetPath = #"C:\Users\me\MinContext.json";
var jsonStr = File.ReadAllText(targetPath);
var parser = new JsonLdParser();
var store = new TripleStore();
parser.Load(store, new StringReader(jsonStr));
var g = store.Graphs.FirstOrDefault();
IUriNode rdfType = g.CreateUriNode("rdf:type");
IUriNode home = g.CreateUriNode("foaf:homepage");
}
On the last line I get this RdfException message:
The Namespace URI for the given Prefix 'foaf' is not known by the
in-scope NamespaceMapper. Did you forget to define a namespace for
this prefix?
...and if you inspect the graph namespaces (g.NamespaceMap.Prefixes) you can see that it only contains three: rdf, rdfs and xsd.
So question: how do I get the foaf prefix and namespace to load correctly?
This is based on using NuGet package version 2.6.1

Prefixes are not an inherent part of any RDF graph, they are just conventions and shortcuts so that you don't have to type the full IRI. A specific database software/implementation can have options for configuring namespaces/prefixes, but they are just for presentation.
In this case, JsonLdParser simply does not import any prefix from the source data into the graph. This is a perfectly valid behaviour, and I don't know if it can be changed. Load can also take IRdfHandlerwhich seems to be able to do something with prefixes, but creating an implementation will most likely be more difficult than simply defining the namespace yourself:
g.NamespaceMap.AddNamespace("foaf", new Uri("http://xmlns.com/foaf/0.1/"));
I'd argue this is actually the more correct option. The source document can specify foaf: to be absolutely anything, but you want this foaf: (the full meaning of a resource name comes from the IRI of its prefix, not from the prefix name itself).
The alternative to that is g.CreateUriNode(new Uri("http://xmlns.com/foaf/0.1/homepage")) which creates a completely equivalent node. Of course it is simpler to add the namespace instead of typing the full IRI every time – that's what namespaces are for.

XmlDsigXPathTransform - namespace prefix is not defined

I am trying to create a signed xml detached signature file using this library: [opensbr]
I need to add an xpath filter to the TransformChain but upon calling SignedXml.ComputeSignature an exception is thrown that the namespace xbrli is not valid.
xpath: /xbrli:xbrl//*[not(local-name()='DocumentAdoptionStatus' or local-name()='DocumentAdoptionDate' and namespace-uri()='http://www.nltaxonomie.nl/8.0/basis/venj/items/bw2-data')]
constructing the transform (as per Microsoft example):
public static XmlDsigXPathTransform CreateXPathTransform(string XPathString)
{
XmlDocument doc = new XmlDocument();
XmlElement xPathElem = doc.CreateElement("XPath");
xPathElem.InnerText = XPathString;
XmlDsigXPathTransform xForm = new XmlDsigXPathTransform();
xForm.LoadInnerXml(xPathElem.SelectNodes("."));
return xForm;
}
The xpath and xml file are both valid.
How can I use namespace prefixes with XmlDsigXPathTransform?

MSDN example* suggests that you can declare namespace prefix on the XPath element :
.....
XmlElement xPathElem = doc.CreateElement("XPath");
xPathElem.SetAttribute("xmlns:xbrl", "xbrl namespace uri here");
xPathElem.InnerText = XPathString;
.....
*) See method LoadTransformByXml in Example #2

The issue here is that prefixes are only locally valid, within a limited scope. Your expression does not contain enough information to resolve your prefix to a namespace (even if it's the same as the default prefix in an XBRL document).
One solution is to "feed" the namespace mapping in code, as suggested by har07.
Another solution is to include the namespace in the complete XPath fragment, on a node level. This is what is used by the Dutch audit profession in official business register filings.
<dsig-xpath:XPath xmlns:dsig-xpath="http://www.w3.org/2002/06/xmldsig-filter2"
xmlns:xbrli="http://www.xbrl.org/2003/instance" Filter="subtract">
/xbrli:xbrl/*[localname()='DocumentAdoptionStatus' or local-name()='DocumentAdoptionDate' or local-name()='EmailAddressContact'] | //text()[normalize-space()='']
</dsig-xpath:XPath>

C# LINQ and XML Getting child nodes

Having issues getting node values. Not sure why the following code is failing to do so.
<?xml version="1.0" encoding="utf-8"?>
<?xml-stylesheet type='text/xsl' href='STIG_unclass.xsl'?>
<Benchmark xmlns:dsig="http://www.w3.org/2000/09/xmldsig#" xmlns:xhtml="http://www.w3.org/1999/xhtml" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:cpe="http://cpe.mitre.org/language/2.0" xmlns:dc="http://purl.org/dc/elements/1.1/" id="Windows_7_STIG" xml:lang="en" xsi:schemaLocation="http://checklists.nist.gov/xccdf/1.1 http://nvd.nist.gov/schema/xccdf-1.1.4.xsd http://cpe.mitre.org/dictionary/2.0 http://cpe.mitre.org/files/cpe-dictionary_2.1.xsd" xmlns="http://checklists.nist.gov/xccdf/1.1">
<status date="2015-06-16">accepted</status>
<title>Windows 7 Security Technical Implementation Guide</title>
<description>
The Windows 7 Security Technical Implementation Guide (STIG) is published as a tool to improve the security of Department of Defense (DoD) information systems. The requirements were developed from DoD consensus, as well as the Windows 7 Security Guide and security templates published by Microsoft Corporation. Comments or proposed revisions to this document should be sent via e-mail to the following address: disa.stig_spt#mail.mil.
</description>
<notice id="terms-of-use" xml:lang="en">Developed_by_DISA_for_the_DoD</notice>
<reference href="http://iase.disa.mil">
<dc:publisher>DISA, Field Security Operations</dc:publisher>
<dc:source>STIG.DOD.MIL</dc:source>
</reference>
<plain-text id="release-info">Release: 20 Benchmark Date: 24 Jul 2015</plain-text>
</Benchmark>
Sample XML File.
and the following is my code.
String Title = LoadedXML.Element("Benchmark").Attribute("id").Value;
var XMLData = LoadedXML.Element("Benchmark").Elements("plain-text")
.Single(release => release.Attribute("id").Value == "release-info").Value;
is there a way I can get multiple Node values at the same time? Like getting the Title and Release Value at once instead of having a separate one for each?

Your code is failing because your XML contains Namespace and you can't access your nodes directly. If you want to confirm this simply query LoadedXML.Elements() and examine the values in debugger, you can clearly see the namespaces there:-
So, You need to declare the namespace and use it:-
XNamespace ns = "http://checklists.nist.gov/xccdf/1.1";
If you want both vales to be fetched at once you can project it to a anonymous type like this:-
var result = LoadedXML.Root.Elements(ns + "plain-text")
.Where(x => (string)x.Attribute("id") == "release-info")
.Select(x => new
{
Title = (string)x.Document.Root.Attribute("id"),
XMLData = x.Value
}).FirstOrDefault();
This query is giving me below output:-

Linq-to-xml is generally used to query a XML to filter it's nodes and then get the desired element/values per need. It's more like querying a table with SQL.
If all/most of the XML is required as a result, then the better approach would be to deseralize the XMl into a native (C# here) object and map it to the required model object. XML can always be thought of a serialized version of an object (although it can be manually as well), and can be deserialized back to the actual object.
.Net has native support for all these, see msdn links for XML Serialization and Deserialization for details. You can write a small method to deserialize your object like this.
using System.Xml.Linq;
using System.Xml.Serialization;
public class XMLHelper
{
public T DeserializeData<T>(string data)
{
XmlSerializer serializer = new XmlSerializer(typeof(T));
StringReader reader = new StringReader(data);
var deserializedObject = serializer.Deserialize(reader);
return deserializedObject == null ? default(T) : (T)deserializedObject;
}
}
To get the string you can do like File.ReadAllText(xmlFilePath) or whatever is easier for the situation.
This will give you deseialized object of the whole XML. If you want some other transformed object, you can either manually map that, or use AutoMapper

Why is the empty namespace not working with .NET System.Xml.XmlNamespaceManager?

I have this XML document:
<?xml version="1.0" encoding="utf-8"?>
<document xmlns="file:///someurl/goes.here">
<levelone>
<leveltwo>
<title>Test Title</title>
<item>Item 1</item>
<item>Item 2</item>
<item>Item 3</item>
</leveltwo>
</levelone>
</document>
And this code:
static void Main(string[] args)
{
XmlDocument fileIn = new XmlDocument();
fileIn.Load("XMLFile1.xml");
XmlNamespaceManager nsm = new XmlNamespaceManager(fileIn.NameTable);
nsm.AddNamespace(String.Empty, "file:///someurl/goes.here");
XmlNode docElem = fileIn.DocumentElement;
string title = docElem.SelectSingleNode("levelone/leveltwo/title", nsm).InnerText;
Console.WriteLine("Title: " + title);
Console.WriteLine("Items: " + docElem.SelectNodes("//item", nsm).Count);
Environment.Exit(0);
}
If I run this, I get a NullReferenceException when I attempt to get the InnerText of the node I'm attempting to select for title. However, if I change my AddNamespace call to nsm.AddNamespace("a", "file:///someurl/goes.here") and update all of my XPaths to use that a namespace, then it works fine.
My understanding is that elements without the prefixes in an XPath refer to the empty namespace. String.Empty is said to be for the empty namespace in MSDN's docs, and I'm giving the NamespaceManager the correct namespace URI for the empty namespace. Yet it doesn't seem to be working and I find myself having to make a dummy namespace in the manager to get it to work right, which is really annoying. Why do I have to use this, or any workaround?
I am not looking for a way to get my code to run, I know of a couple ways and detailed one widely-accepted method above. I want to know why my understanding of the documentation is resulting in broken code - e.g. is this an issue on Microsoft's end or am I just misunderstanding something?

Creating an XmlElement without a namespace

I am using the CreateElement() method of my XmlDocument like this:
XmlElement jobElement = dom.CreateElement("job");
But what I get in the outcome is a job element with an empty namespace.
<job xmlns="">xyz</job>
And the program that is supposed to read this Xml will no longer detect this job element.
I thought this question gives an answer, but it does not. How can I create a pure job element?
<job>xyz</job>
Update: This is the root element of my document:
<job-scheduling-data xmlns="http://quartznet.sourceforge.net/JobSchedulingData" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" version="2.0">

"I thought this question gives an answer, but it does not."
Actually it does. Set <job> element to be in the default namespace (unprefixed namespace that, in this case, was declared at the root level) :
XmlElement jobElement = dom.CreateElement("job", "http://quartznet.sourceforge.net/JobSchedulingData");
jobElement.InnerText = "xyz";
This way, in the XML markup, <job> element simply inherits it's ancestor's default namespace (no local-empty default namespace will be created) :
<job>xyz</job>