can you have complex types which are multivalued? I'd like to store something like a tag-name with a corresponding tag-weighting.
How much work it is might depend on how static or dynamic the tag-weighting is. If it's very static, you could simply use index-time boosts.
can you do sum(*) type queries in lucene/solr? it is efficient ?
If all tag weights were the same, you would get summing for "free" via lucene scoring I think... It all depends on the exact details of what you are trying to do, how many tags, how are the weights calculated, are the sums across all tags or dynamically determined by some query, etc... -Yonik