The App Engine datastore stores and performs queries over data objects, known as entities. An entity has one or more properties, named values of one of several supported data types. A property can be a reference to another entity.
The datastore can execute multiple operations in a single transaction, and roll back the entire transaction if any of the operations fail. This is especially useful for distributed web applications, where multiple users may be accessing or manipulating the same data object at the same time.
Unlike traditional databases, the datastore uses a distributed architecture to manage scaling to very large data sets. An App Engine application can optimize how data is distributed by describing relationships between data objects, and by defining indexes for queries.
The App Engine datastore is strongly consistent, but it's not a relational database. While the datastore interface has many of the same features of traditional databases, the datastore's unique characteristics imply a different way of designing and managing data to take advantage of the ability to scale automatically.
Continue to Data Modeling.