A Database is an integrated collection of logically related records or files consolidated into a common pool that provides data for one or more multiple uses. One way of classifying databases involves the type of content, for example: bibliographic, full-text, numeric, image. Other classification methods start from examining database models or database architectures: see below. Software organizes the data in a database according to a database model. As of 2009 the relational model occurs most commonly. Other models such as the hierarchical model and the network model use a more explicit representation of relationships.
Object databases use a range of storage mechanisms. Some use virtual memory-mapped files to make the native language (C++, Java etc.) objects persistent. This can be highly efficient but it can make multi-language access more difficult. Others break the objects down into fixed- and varying-length components that are then clustered tightly together in fixed sized blocks on disk and reassembled into the appropriate format either for the client or in the client address space. Another popular technique involves storing the objects in tuples (much like a relational database) which the database server then reassembles for the client.
Simple Object database example.
Other important design choices relate to the clustering of data by category (such as grouping data by month, or location), creating pre-computed views known as materialized views, partitioning data by range or hash. Memory management and storage topology can be important design choices for database designers as well. Just as normalization is used to reduce storage requirements and improve the extensibility of the database, conversely denormalization is often used to reduce join complexity and reduce execution time for queries.