Which of the following about JOIN operations is/are correct?试题 12选择一项或多项：a.The lack of JOIN operations in a NoSQL database leads to the issues of data redundancy and data integrity.b.The JOIN operations are essential for developing efficient autosharding technologies.c.The JOIN operations are not common in NoSQL databases because they could make the query processing slow.d.MongoDB supports a JOIN operator, similar to relational databases.

In relation to a Graph Database which of the following are correct?试题 5选择一项或多项：a.Compared with key-value data stores, graph databases generally have more complex data models but are less scalable.b.Neo4j does not support the join operation.c.In a graph database we represent data in terms of graphs having two fundamental units being nodes and relationships and while noes may have properties relationships are not allowed to have properties.  d.Graph databases can navigate through graphs to answer queries, and thus they always provide a better performance for queries than relational databases.

What is/are the reason(s) for considering a NoSQL database, rather than a relational database?试题 11选择一项或多项：a.To support a declarative query language for querying data and managing data integrity.b.To support complex transactions to preserve consistency across difference transactions.c.To support the insertion of data without a pre-defined schema.d.To support high-performance queries over an extremely large amount of data, while update operations are rare.

Which of the following is/are correct?试题 10选择一项或多项：a.There are no transactions in any NoSQL databases.b.NoSQL databases define isolation levels under the BASE model .c.Different NoSQL databases may offer different levels of transaction supports.d.Some NoSQL databases let the programmer decide the trade-off between scalability and consistency.

Which of the following is/are correct?试题 6选择一项或多项：a.Dynamo doesn’t require a rigid schema before inserting data.b.MongoDB supports the concepts of primary key and foreign key.c.Google's Bigtable does not support schema.d.The concept of schema in MongoDB is flexible, which allows programmers to modify data structure at runtime.

Dynamo is a NoSQL database developed by Amazon. Which of the following about Dynamo is/are correct?试题 8选择一项或多项：a.Dynamo is targeted mainly at applications where no updates are rejected due to concurrent writes.b.Dynamo uses the technique of consistent hashing to map each node to a single datacenter.c.Dynamo is designed to achieve strong consistency and high data availability simultaneously.d.Dynamo provides security related support for managing data, such as authentication and authorization.