10. A non-transitory computer-readable storage medium storing executable computer program instructions for performing a relationship-based search, the computer program instructions comprising instructions for: receiving a user query from a user, the user query including a reference to a query object; processing the user query into a plurality of sub-queries for information related to the query object, each sub-query being for a corresponding one of a plurality of information sources; submitting the plurality of sub-queries to the plurality of information sources; receiving search results for the plurality of sub-queries from the information sources, each search result identifying (a) a search result object related to the query object and (b) a type of relationship indicating a type of relevancy of the search result to the search query; organizing the search results into a plurality of categories based on types of objects identified in the search results, wherein each of the plurality of categories includes a respective type of objects, the plurality of categories including a first category comprising a first subset of search results with a first object type and a second category comprising a second subset of search results with a second object type; organizing the first subset of search results in the first category into a plurality of buckets based on types of relationships indicating types of relevancy of the first subset of search results to the search query, each bucket including search results with a respective type of relationship with the search query, the plurality of buckets including a first bucket comprising a first further subset of the first subset of search results in the first category with a first type of relationship with the search query and a second bucket comprising a second further subset of the first subset of search results in the first category with a second type of relationship with the search query; and providing the search results organized into the plurality of categories, the provided search results including the first subset of search results in the first category organized into the plurality of buckets for presentation to the user.
10. A non-transitory computer-readable storage medium storing executable computer program instructions for performing a relationship-based search, the computer program instructions comprising instructions for: receiving a user query from a user, the user query including a reference to a query object; processing the user query into a plurality of sub-queries for information related to the query object, each sub-query being for a corresponding one of a plurality of information sources; submitting the plurality of sub-queries to the plurality of information sources; receiving search results for the plurality of sub-queries from the information sources, each search result identifying (a) a search result object related to the query object and (b) a type of relationship indicating a type of relevancy of the search result to the search query; organizing the search results into a plurality of categories based on types of objects identified in the search results, wherein each of the plurality of categories includes a respective type of objects, the plurality of categories including a first category comprising a first subset of search results with a first object type and a second category comprising a second subset of search results with a second object type; organizing the first subset of search results in the first category into a plurality of buckets based on types of relationships indicating types of relevancy of the first subset of search results to the search query, each bucket including search results with a respective type of relationship with the search query, the plurality of buckets including a first bucket comprising a first further subset of the first subset of search results in the first category with a first type of relationship with the search query and a second bucket comprising a second further subset of the first subset of search results in the first category with a second type of relationship with the search query; and providing the search results organized into the plurality of categories, the provided search results including the first subset of search results in the first category organized into the plurality of buckets for presentation to the user. 14. The non-transitory computer-readable storage medium of claim 10 , wherein the first category includes search results that identify people type objects, the query object identifies a person, and the types of relationships include at least one of: people included in email threads with the person, people with meetings in common with the person, people belonging to a same organization as the person, and people sharing a postal address with the person.