CHAPTER 23 Introducing PDO The (Tomcat web server)
CHAPTER 23 Introducing PDO The number of available software solutions is simultaneously a blessing and a curse. While this embarrassment of riches is of great advantage to end users, allowing them to find products that meets their specific needs, it s long proven to be a nightmare for developers and system administrators, requiring that two or more distinct products transparently interoperate. Although adherence to standards such as XML is greatly contributing to interoperability efforts, we re still years away from any widespread resolution. This problem is particularly pronounced for applications requiring a database back end. While all mainstream databases adhere to the SQL standard, albeit to varying degrees, the interfaces that programmers depend upon to interact with the database can vary greatly (even if the queries are largely the same). Therefore, applications are almost invariably bound to a particular database, forcing users to also install and maintain the required database if they don t already own it, or alternatively to choose another, possibly less-capable solution that is compatible with their present environment. For instance, suppose your organization requires an application that runs exclusively on Oracle, but your organization is standardized on an open-source database. Are you prepared to invest the considerable resources required to purchase the necessary Oracle licenses, and prepared to maintain the database, all for the sake of running this particular application? To resolve such dilemmas, enterprising programmers began developing database abstraction layers, which serve to decouple the application logic from that used to communicate with the database. By passing all database-related commands through this generalized interface, it became possible for an application to use one of several database solutions, provided that the database supported the features required by the application, and that the abstraction layer offered a driver compatible with that database. A graphical depiction of this process is found in Figure 23-1.
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