On the PHP on Windows section of DZone.com today Giorgio Sironi has posted about a different sort of object mapping than is usually thought of with databases - object-document mapping.
The Data Mapper pattern is a mechanism for persistence where the application model and the data source have no dependencies between each other. [...] But everytime we talk about the Data Mapper pattern, we assume there is a relational database on the other side of the persistence boundary. We always save objects; we always map them to MySQL or Postgres tables; but it's not mandatory.
He talks about two projects, MongoDb_ODM and CouchDb_ODM, that the Doctrine project is working on to help make working with document-driven databases as simple as the usual ORMs. He includes a brief code snippet showing how the feature will work (hint: a namespace of Document instead of Entity). He lists some of the features - including the usual ORM capabilities, support for collections, cascade of persistence - and where you can get the latest code for it (from github and PEAR