The Accessor Layer
In a multiple-tier PHP software architecture, only one layer (comprising one set of PHP programs) accesses the persistence layer, which is otherwise known as the database or filesystem. That’s the accessor layer.
When, as is usually the case, the persistence layer is a database server, the accessor layer has a lot to do with commands that manipulate the database. In other words, the accessor programs contain lots of structured query language (SQL) statements that add data to the database, remove data from the database, modify data already in the database, and extract particular sets of data from the database.
However, because the accessor layer must deal with the peculiarities of the database server to which it has ...
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