Beyond the database schema changes and the small differences in the code's beginning and ending, described above, software incorporating the hybrid database can be moved seamlessly between the different set-top box types, disk-enabled and disk-less.

No changes are needed in the body of the application; the system stores data on the hard disk (or flash memory, SD card, etc.) of a device with permanent media, and stores records entirely in memory within a disk-less box.

This contrasts sharply with the major alterations in code required to port an application between two different database systems, as would be required using a dedicated on-disk database system, and one designed for in-memory storage only.

Approaches to error-handling, database locking, and transaction models are just some of the areas where database systems can differ radically, even when the separate DBMSes are generally considered "embedded databases." Accommodating these differences typically demands substantial changes in program logic.

One especially thorny area when moving between DBMSs is application programming interfaces (APIs), which vary widely between database software vendors. "Ripping out the database" is common programmer slang for moving an application from one DBMS to another.

It accurately describes the code disruption of taking out the "stitching" that the API provides between application logic and database system. Functions comprising one database system's API often do not map directly to another DBMS, often requiring substantially different syntax and arguments.

Using an API that supports the ANSI SQL and open database connectivity (ODBC) APIs standards can mitigate the pain of moving between databases, but to be 100% portable (or as close as possible) a developer would have to stay away from any vendor's advantages and be satisfied with a least-common-denominator solution. Developers are rarely eager to do that.

With eXtremeDB Fusion, DIRECTV gained the ability to design a unified software platform, incorporating one embedded database, for both disk-less and disk-enabled set-top boxes. To adapt the applications between these hardware environments, the company's developers still must make changes at both the database design and application code levels.

However, the porting is greatly simplified. It is safe to say that programmer-weeks are saved in initial development of the software platform, and even greater savings should occur post-release, as the efficiencies are gained from maintaining and extending one code base rather than two.

As software applications increasingly reside on embedded devices (rather than desktop or server computers), and as manufacturers offer more feature-set choices within product lines, then embedded software engineers increasingly face target environments that are split between disk-enabled and disk-less devices.

Hybrid database systems help developers meet this challenge while preserving much of the database coding simplicity of dealing with a single approach to data storage.

Steve Graves is CEO and founder of McObject