Are vertex_index, edge_index and fulltext_index collections used for indexing in Atlas?

[#1]

I am using the following guide (link: http://atlas.incubator.apache.org/InstallationSteps.html) for building and installing Atlas.

In the guide the user needs to create three collections in Solr, vertex_index, edge_index and fulltext_index. I would like to know what is the purpose of these and how do they work in order to index?

Also, how does indexing work in Atlas?

Thanking you in anticipation.

[#2]

These following are the SOLR indexes that Atlas typesystem use:

1. vertex_index - A mixed index - fields like guid, type, timestamp and state are indexed so they can be used in any combination during search query.
2. edge_index - We don't use this index much in Atlas, this is added to enable indexing on edge properties.
3. fulltext_index - used for fulltext search. The indexed fields (entityText) are tokenized to enable faster retrieval.

To know more about how indexes work in Atlas: http://s3.thinkaurelius.com/docs/titan/0.5.4/indexes.html

Hope this helps.