Efficient data storage and retrieval (e.g., in terms of time and space requirements) is facilitated by implementing an indexing structure comprising an indexing array. That is, a functional relationship between elements of a source set and elements of a query result set can be stored in the indexing structure. This allows, for example, a query regarding whether an element is a member of a set (e.g., whether a particular website or Uniform Resource Locator (URL)) has been visited before) as well as a relationship between the member set and the query (e.g., the number of hyperlinks in the website the last time it was visited) to be resolved efficiently.