What can an RDBMS do that Neo4j (and graph databases) cant?

Question

“A Graph Database –transforms a–> RDBMS”

The Neo4j site seems to imply that whatever you can do in RDBMS, you can do in Neo4j.

Before choosing Neo4j as a replacement for an RDBMS, I need some doubts answered.

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I am interested in Neo4j for

• ability to do quickly modify data "schema"
• ability to express entities naturally instead of relations and normalizations
• ...which leads to highly expressive code (better than ORM)

This is a NoSQL solution I am interested in for it's features, not high performance.

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Question: Does Neo4j present any issues that may make it unsuitable as a RDBMS replacement?

I am particularly concerned about these:

• is there any DB feature I must implement in application logic? (For example, you must implement joins at application layer for a few NoSQL DBs)
• Are the fields "indexed" to allow a lookup faster than O(n)?
• How do I handle hot backups and replication?
• any issues with "altering" schema or letting entities with different versions of the schema living together?

Answer 1

This is an extremely broad topic covering everything from modeling and implementation to IT and support. It's impossible to really answer all those questions here, especially without details on your situation. However, you seem to be exploring options and avenues. So, I'll just pass on some general food for thought as someone that's implemented a number of systems.

Everybody seems to think their new database paradigm is a replacement for relational databases. So, take those claims with a grain of salt.

I like to think in terms of 3 fundamental models: Relational, Document, and Graphing. Depending on your problem space one or even more of these is the right answer. I would not do financial transactions in anything but relational (SQL Based). If you are building a CMS, then a Document DB is the way to go. If my application is modeling networks (roads, people, connections, networks etc.) I use Neo4J.

As far as production quality, there are solid options in each category. Relational has a bunch. For document databases I'd go MongoDB or a higher level JCR system like Apache Jackrabbit. For graphing, I only have experience with Neo4j and it is rock solid for me.

Whatever you do, don't buy into the hype that "We have the one technology that solves all your problems." It's not there and it narrows your thinking.