How to query the rdf format data?

Question

I am new in both rdf and BDB XML, and I have got some problems while using both. Now, I am eager for your help.
I wrote a simple rdf file which can be validated in [http://www.w3.org/RDF/Validator].
{color:#0000ff}<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:class="http://www.ict.ac.cn/e_learning#">
<rdf:Description rdf:about="Chinese">
<class:ID>0000001</class:ID>
<class:teacher>Kongzi</class:teacher>
<class:classroom>101</class:classroom>
<class:lesson>0000000001</class:lesson>
<class:year>2007</class:year>
</rdf:Description>
<rdf:Description rdf:about="Math">
<class:ID>0000002</class:ID>
<class:teacher>Gauss</class:teacher>
<class:classroom>102</class:classroom>
<class:lesson>0000010001</class:lesson>
<class:year>2008</class:year>
</rdf:Description>
</rdf:RDF>
{color}
I create a container, put the content listed above into the container as a document. But no matter what I want to query, for example, {color:#0000ff}"collection('learn')/rdf:RDF/rdf:Description[@rdf:about='Math']"{color}("learn" is the alias), does it return no results. But when I change the "{color:#0000ff}rdf:Description{color}" into whatever other words like "{color:#0000ff}rdf:aaa{color}", in both document and query expression, the results are right. My BDB XML version is 2.4.16.
Could anybody help? Thank you very much!
Edited by: user10795743 on 2009-2-2 下午11:29

Answer 1

Hi,
Just try to set namespace and alias explicitly. Maybe your namespace/alias is not set correctlly.
I've use dbxml shell to test:
1. Create container and document for test.
dbxml> createcontainer learn.xml
dbxml> addAlias learn
Added alias: learn
dbxml> putdocument doc1.xml '<?xml version="1.0"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:class="http://www.ict.ac.cn/e_learning#">
<rdf:Description rdf:about="Chinese">
<class:ID>0000001</class:ID>
<class:teacher>Kongzi</class:teacher>
<class:classroom>101</class:classroom>
<class:lesson>0000000001</class:lesson>
<class:year>2007</class:year>
</rdf:Description>
<rdf:Description rdf:about="Math">
<class:ID>0000002</class:ID>
<class:teacher>Gauss</class:teacher>
<class:classroom>102</class:classroom>
<class:lesson>0000010001</class:lesson>
<class:year>2008</class:year>
</rdf:Description>
</rdf:RDF>'2. set namespace
dbxml> setnamespace rdf http://www.w3.org/1999/02/22-rdf-syntax-ns#
Binding rdf -> http://www.w3.org/1999/02/22-rdf-syntax-ns#
dbxml> setnamespace class http://www.ict.ac.cn/e_learning#
Binding class -> http://www.ict.ac.cn/e_learning#3. query
dbxml> query 'collection("learn")/rdf:RDF/rdf:Description'
2 objects returned for eager expression 'collection("learn")/rdf:RDF/rdf:Description'4; result
dbxml> print
<rdf:Description xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" rdf:about="Chinese">
<class:ID xmlns:class="http://www.ict.ac.cn/e_learning#">0000001</class:ID>
<class:teacher xmlns:class="http://www.ict.ac.cn/e_learning#">Kongzi</class:teacher>
<class:classroom xmlns:class="http://www.ict.ac.cn/e_learning#">101</class:classroom>
<class:lesson xmlns:class="http://www.ict.ac.cn/e_learning#">0000000001</class:lesson>
<class:year xmlns:class="http://www.ict.ac.cn/e_learning#">2007</class:year>
</rdf:Description>
<rdf:Description xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" rdf:about="Math">
<class:ID xmlns:class="http://www.ict.ac.cn/e_learning#">0000002</class:ID>
<class:teacher xmlns:class="http://www.ict.ac.cn/e_learning#">Gauss</class:teacher>
<class:classroom xmlns:class="http://www.ict.ac.cn/e_learning#">102</class:classroom>
<class:lesson xmlns:class="http://www.ict.ac.cn/e_learning#">0000010001</class:lesson>
<class:year xmlns:class="http://www.ict.ac.cn/e_learning#">2008</class:year>
</rdf:Description>