Why Use an Embedded Database?

whenever applications provide their own database management, those databases are called embedded. In a sense, they can be seen as being embedded in the application, as well as on the local system.

At one time, databases of this kind were the norm. Consider, for example, that COBOL has built-in primitives for creating and maintaining embedded databases. These are true primitive keywords of the language, they are not even function calls. Today, FoxPro and similar languages come closest to this model. In the heyday of COBOL and xPro languages, client-server relational database management systems were not common. As a result, these languages often created local data stores, which were used by the immediate application. Later on, data records would be exported to a central database as needed.

Embedded DB in Applications
Suppose you were designing a utility like Microsoft Outlook, which provides a GUI front end for entry of appointments, contacts, and individual e-mails. How would you handle the data management of these records? Likely, you would want a database to do this for you, but you'd be in a bit of jam deciding how to choose one. The first problem is that you cannot rely on the customer having any particular database, to serve as a back-end to your software. You could compensate for this by providing a generic database front-end (say, with ODBC, JDBC, or the like) and then have the customer map it to the DBMS in use at their site. But if the customer is a consumer running your productivity suite on an occasionally connected notebook, what are you going to do? The solutions is: You provide your own DBMS in the form of an embedded database. Later, if this embedded database has to sync with another (such as Outlook synching with Microsoft Exchange or with a handheld device), you rely on application-level data import and export functions to perform this function.

Consumer-oriented software is a clear, definable market for embedded databases. Candidate applications include accounting software, portfolio tracking, and so on. Today, each of these applications comes with its own embedded data store. The best embedded databases have several traits in common: they don't consume a lot of resources, they're fast, and they are utterly reliable—three qualities that consumer products must deliver in today's highly competitive markets.

ref:
http://www.devx.com/IBMDB2/Article/27622