In order to retrieve something, you need to know where to find it – in other words, its address.
An address doesn't have to be an absolute location; you can address things relatively ("two doors down from 29 Jones St."). It doesn't have to be an explicit location at all: you can address things by name ("Lance") or description ("world's greatest athlete").
You can address several things at once ("Monty and Westy"), even if you don't know exactly what they are or whether they even exist ("inexpensive French restaurant downtown").
All those forms of address can be used to locate things in XML documents, by means of an XPath expression.
The most important form of XPath expression is called a location path. You may already be familiar with location paths because they are used to address your computer's files by specifying the path from the file system's root to a specific subdirectory. For example, the path /home/bob/xml/samples identifies a particular one of the four samples subdirectories shown in Figure 17-1.
