这些依赖于下面的层以及所有使用它们的应用程序，所以，理想情况下，在应用程序被建造在它们之上之前，它们十分地稳定。
These depend upon the layer below, and all applications that use them depend on them, so, ideally, they are pretty stable by the time that applications are built atop them.
MapServer要提供地图图片，必须被告知要使用的层以及如何呈现。
MapServer, to provide a map image, must be told what layers to use and how to render them.
本系列中的下一篇文章描述Drupal数据库抽象层，以及如何使用DB 2 Express - c替代mysql或PostgreSQL。
The next article in this series describes the Drupal database abstraction layer, and how DB2 Express-C could be used as an alternative to MySQL or PostgreSQL.
应用推荐