Is it suitable and efficient to use RDF in such an application?

Hi,
    I'm a newbie of RDF, so my questions may be a little naive. Thanks a lot if somebody could help me.

    I'm doing a project called InforBroker which disseminate all kinds of information to clients.
Every piece of information has some metadata. I want to use RDF to describe these metadata. Each RDF file may be like the following:

<?xml version="1.0"?>
<RDF xmlns="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
     xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
     xmlns:ITS="http://www.otc.org/ITS#">
<Description about="www.reutoer.org/news/12334"> 
    <ITS:InforSource>  Reuter  </ITS:InforSource>
    <ITS:category>  economy  </ITS:category>
    <ITS:Title>Toronto Stocks Close 3.5 Percent Up In Late Rally </ITS:Title>
    <ITS:Creator>Stuart Weibel</ITS:Creator>
    </Description>
</RDF>

    The clients may hold several pieces of information.  A natural way is to categorize them. So  I want to build a tree view on client's end. A tree is dynamically constructed by the properties of the RDF file. For example, he may want to view information by <ITS:InforSource>, by <ITS:Category>, or by combination of them. for example, a tree node is "Reuter", it contains all the information sent by retuer. Here the amount of information souce and category is countable.    You may imagine we have an Windows Explorer, but the tree view of the explorer is changed dynamically by users' commands such as "categorized by information source", or "categorized by author".
    Each time users opens my client, I should build the tree, I wonder I have to build an index for each property to may the construction process quicker. It seems that I have to merge all the rdf files associate with each piece of information to make parsing process quicker. I wonder if there is some RDF APIs suitable for such an application. I read "Summary of Recent Discussions about an API for RDF", but no help. Also I wonder if I could store it to some database, it seems more efficient. 
    Thanks if somebody could give me some suggestions.
    
Tong.