8.1 Introduction

POET Software, a leading vendor of object-oriented databases, has developed a new database management system named Navajo for mobile and embedded devices. Design and development have faced several special challenges: robustness, low-resource consumption, and connectivity.

A database management system for mobile and embedded devices must be able to run nonstop perhaps for years because such devices typically are not shut down; instead, they are placed in suspend mode. Obviously, the database must require zero administration. A transaction model that includes full recovery and different models of concurrency is needed to support background updates and synchronization. Low-resource consumption means that the database kernel is restricted in terms of code size, use of main memory, and persistent storage. Apart from technical considerations (e.g., compression, dynamically reconfigurable caches, and swapping algorithms), the problem is tackled on a conceptual level by choosing a strictly modular approach. The application developer or device manufacturer chooses the set of features required for a particular application and assembles the database configuration from the modules that enable these features. For example, all mobile and embedded scenarios require the device and its database to be occasionally connected to a PC, a company network, or the internet. The database system needs to download new data (delivery) or upload data obtained when the device was offline (archiving). More generally, it needs to synchronize with other data stores. Facilities such as logging, import and export, and replication need to be provided as plug-ins to help the application developer solve individual connectivity...