DBpedia getting page category using sparql

I am using DBpedia to getting page category using SPARQL in R. However, there are having some problems on it. Source code I am using:

PREFIX dcterms: <http://purl.org/dc/terms/>
PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>  
SELECT ?categoryUri ?categoryName WHERE {
    <http://dbpedia.org/resource/xxx> dcterms:subject ?categoryUri.
         ## xxx are random words (e.g. Agree, Film, Work, Plan...)
    ?categoryUri rdfs:label ?categoryName.
    FILTER (lang(?categoryName) = "en")
}

The problems are:

Category cannot be retrieved if the words need to be redirected (e.g. Agree -> Agreement)
Disambiguation pages cannot be used from the above source code, because there are so many sub-pages within the category of word (e.g. Work)

So, how can I resolve the above problems? I am really appreciate if anyone can offer your help!!!

SPARQL does only do what you write, so there is no magic behind. If some resource :s is possibly connected to others by a property :p, add a triple pattern :s :p ?o . - sometimes you might even consider to use a property path in case of the resolution of the transitive closure of :p, i.e. :s :p* ?o ..

With redirects resolved:

PREFIX  dbo:  <http://dbpedia.org/ontology/>
PREFIX  dcterms: <http://purl.org/dc/terms/>

SELECT * WHERE
  { <http://dbpedia.org/resource/Agree> (dbo:wikiPageRedirects)* ?page
    OPTIONAL
      { ?page dcterms:subject ?categoryUri}
  }

Note the OPTIONAL clause, which is necessary here because not all resources in DBpedia belong to a category.

Including disambiguation pages:

PREFIX  dbo:  <http://dbpedia.org/ontology/>
PREFIX  dcterms: <http://purl.org/dc/terms/>

SELECT * WHERE
  { <http://dbpedia.org/resource/Agree> (dbo:wikiPageRedirects)*/(dbo:wikiPageDisambiguates)* ?page
    OPTIONAL
      { ?page dcterms:subject ?categoryUri}
  }