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| <h1 class="title">ARQ - Frequently Asked Questions</h1> |
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| <p>java.lang.NoClassDefFoundError : Exception in thread “main” |
| : The classpath is wrong. Include all the jar files in lib/ |
| before running one of the command line applications.</p> |
| <p>java.lang.NoSuchFieldError: actualValueType |
| : This is almost always due to using the wrong version of the |
| <a href="http://xml.apache.org/xerces2-j/">Xerces</a> library. Jena and ARQ |
| make use of XML schema support that changed at Xerces 2.6.0 and is |
| not compatible with earlier versions. At the time of writing Jena |
| ships with Xerces 2.6.1.</p> |
| <pre><code>In some situations your runtime environment may be picking up an |
| earlier version of Xerces from an "endorsed" directory. You will |
| need to either disable use of that endorsed library or replace it |
| by a more up to date version of Xerces. This appears to happen with |
| some distributions of Tomcat 5.\* and certain configurations of JDK |
| 1.4.1. |
| </code></pre> |
| <p>Query Debugging |
| : Look at the data in N3 or Turtle or N-triples. This can give |
| you a better sense of the graph than RDF/XML.</p> |
| <pre><code>Use the [command line tools](cmds.html) and a sample of your data |
| to develop a query, especially a complex one. |
| |
| Break your query up into smaller sections. |
| </code></pre> |
| <p>How do I do test substrings of literals? |
| : SPARQL provides regular expression matching which can be used |
| to test for substrings and other forms that SQL’s LIKE operator |
| provides.</p> |
| <pre><code>Example: find resource with an RDFS label contains the substring |
| "orange", matching without respecting case of the string. |
| |
| PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#> |
| SELECT ?x |
| WHERE { |
| ?x rdfs:label ?v . |
| FILTER regex(?v, "orange", "i") |
| } |
| |
| The regular expression matching in ARQ is provided by |
| java.util.regex. |
| </code></pre> |
| <p>Accented characters and characters outside of basic latin |
| ~ SPARQL queries are assumed to be Unicode strings. If typing |
| from a text editor, ensure it is working in UTF-8 and not the |
| operating system native character set. UTF-8 is not the default |
| character set under MS Windows.</p> |
| <pre><code>ARQ supports \\u escape sequences in queries for the input of 16bit |
| codepoints. |
| |
| ARQ does not support 32 bit codepoints (it would require a move to |
| Java 1.5, including all support libraries and checking the codebase |
| for char/codepoint inconsistencies and drop support for Java 1.4). |
| |
| The same is true for data. XML files can be written in any |
| XML-supported character set if the right `?xml` processing |
| instruction is used. The default is UTF-8 or UTF-16. |
| </code></pre> |
| <p>XSD DateTime |
| : Examples of correctly formatted XSD DateTime literals are: |
| these two are actually the same point in time and will test equal |
| in a filter:</p> |
| <pre><code> "2005-04-04T04:04:04Z"^^xsd:dateTime |
| "2004-12-31T18:01:00-05:00"^^<http://www.w3.org/2001/XMLSchema#dateTime> |
| |
| - The timezone is required. |
| - The datatype must be given. |
| </code></pre> |
| <p>String Operations |
| : ARQ provides many of the XPath/XQuery functions and operators |
| including string operations. These include: |
| <code>fn:contains</code>, <code>fn:starts-with</code>, <code>fn:ends-with</code>. See the |
| <a href="library-function.html">library page</a> for details of all function |
| provided.</p> |
| <pre><code>Note 1: For string operations taken from XQuery/XPath, character |
| positions are numbered from 1, unlike Java where they are numbered |
| from 0. |
| |
| Note 2: `fn:substring` operation takes the length of the substring |
| as the 3rd argument, unlike Java where it is the end index. |
| </code></pre> |
| <p><a href="index.html">ARQ documentation index</a></p> |
| |
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