When I started working on computers, the main thing people used databases for was storing tabular data. Sales reports, inventory records, lists of things. Relational databases were cool because you could associate a transaction in your sales table with an item in your inventory table. As the internet has grown, however, our database needs have outgrown the abilities of the standard relational database system. Social networks are a great example of this – the type of query needed to ask for six degrees of Kevin Bacon separation in a relational database is complex, resource intensive, and extremely time consuming. Many very smart people have come up with ways to work around this problem, but the real problem is that this type of question is not what relational databases are designed to handle.