I've just started a new job where I'm going to have to do a fair amount of work with a multi-value database (UniVerse). What little database experience I have is in relational databases (SqlServer) and I'm looking for some un-biased information about what the pros and cons of a MVD are compared to relational databases.
Everyone in the office either comes from a relational database background (and hates UniVerse) or has been here for years and loves it.
First, a disclaimer. I work with UniData (the sister DB of UniVerse) and occasionally blog on it, so I cannot claim to be completely unbiased; I will try, however.
Here are some points of consideration for you:
A big difference between an SQL DB and a Multivalue DB is that the MVDB does not adhere to 1NF. This has pros and cons to it. It can be (and commonly is) abused, but there are times when it can be extremely functional. The biggest benefit is that it means you don't always need a join table which can make certain queries much faster.
It stores meta-data in a completely novel manner when compared to regular SQL DBs. Each file/table does not have a concrete schema. Instead, it has 1 or more 'dictionary' files which is made up of records that tell you how the data should be interpreted. This allows you to have not only store multiple interpretations of the data (raw/uppercase/lowercase, combined fields, etc) but also allows you to perform the equivalent of enums and joins. It can be extremely powerful if done right.
Sadly, although the concept has much potential, the DBMS's toolset is lacking. Development is driven but a extremely small set of businesses cases that appear to be driven by a 'keep-the-lights-on' mentality of existing & aging software systems that were built on it. Although it has tools for integration (such as .NET connectors, ODBC interface for SQL queries, etc) they do have issues. For example, the UniObjects .NET interface lacks any granulation in security (basically all or nothing).
It isn't just a DBMS, but is essentially an entire application platform. Even though UniBasic isn't as powerful as say a .NET based language, it sure beats the pants off T-SQL and has a fast turn around for pumping out business rules.