dataset API, query any federated dataset

[bplatz]

The allows federated query of any number of graph dbs across any number of connections with any unique configurations per db desired (permissions, time-travel).

In order to query against any arbitrary set of graph dbs, you compose those dbs together using the new API dataset.

e.g. to compose these 3 dbs into a single dataset:

(let [authors (fluree/db @(fluree/ledger conn1 "my/authors"))
      books   (fluree/db @(fluree/ledger conn1 "my/authors"))
      movies  (fluree/db @(fluree/ledger conn1 "my/authors"))
      ds      (fluree/dataset {"test/authors" authors
                               "test/books"   books
                               "test/movies"  movies})]
  @(fluree/query ds <query-here>))

In this case, all the dbs are composed as a default graph, but they can still be targeted invidually for specific where statements using the graph function:

  {...
   'where': [...
             ['graph' <graph-alias> <query-pattern>]]
   ...}

If you'd like to have only specific dbs part of the "default graph", you can supply the alias names as a list with a second argument to fluree/dataset:

(def ds (fluree/dataset {"test/authors" authors
                         "test/books"   books
                         "test/movies"  movies}
                         ["test/books", "test/movies"])

In this case, only test/books and test/movies would be part of the default graph.

This closes issue: https://github.com/fluree/core/issues/96

[dpetran]

Will we also support datasets in transactions? Say I want to update data in one graph based on data in another graph.