If you've been wanting to get into document databases (NoSQL stuff) but haven't had a good beginners guide to look at, Derick Rethans has just the post for you. It introduces some of the concepts behind these databases with just a splash of how to use it in PHP.

By now most you will probably have heard of the term NoSQL. It's a vague term that covers a lot of different types of database engines. The main classes of NoSQL databases are key/value stores, column databases, graph databases and document databases. [...] Apache CouchDB and http://mongodb.org/">MongoDB belong to the last category, Document databases. We will be looking extensively at MongoDB in this article.

He starts off with some explanation of basic terminology and quickly gets into some of the strengths of a document-oriented database. He talks about data models and collection interaction as well as an example query translated from ANSI SQL to the MongoDB format. He has a basic installation and configuration guide, both for MongoDB and installing the PHP driver you'll need to make the connection.