Q: is Sandra a document DB? Hierarchical for sure. I think it is a graph DB with a hierarchical interface
Q: which category most resembles RDBMS?
–category: graph DB? lest used, most specialized. Not worth learning
–category: bigtable clones i.e. columnar DB? less used in the finance projects I know.
–category: document store
- hierarchy — JSON and XML
- query into a document is supported (In contrast, key-value store is opaque.) Index into a document?
- index is absolutely needed to avoid full table scan
- search by a common attribute
- hierarchical document often contains maps or lists in an enterprise application. I think it’s semi-structured. More flexible than a RDBMS schema
–category: distributed hashmap.
- Key must support hashing. Value can be anything
- Value can be a hierarchical document !
- Opaque — What if your value objects have fields? To select all value objects having a certain field value, we may need to use the field value as key. Otherwise, full table scan is inevitable. I think document store supports query on a field in a document. However, I think Gemfire and friends do support query into those fields.